simulation/plugins/SimpleDronePlugin.cc

#include <gazebo/gazebo.hh>
#include <gazebo/physics/physics.hh>
#include <gazebo/common/common.hh>
#include <gazebo/common/Image.hh>
#include <gazebo/sensors/sensors.hh>
#include <gazebo/sensors/CameraSensor.hh>
#include <gazebo/rendering/Camera.hh>
#include <ignition/math/Vector3.hh>
#include <ignition/math/Pose3.hh>

#include <boost/filesystem.hpp>

#include <vector>
#include <string>
#include <cstdlib>
#include <cmath>
#include <fstream>
#include <functional>
#include <sstream>
#include <ctime>
#include <algorithm>
#include <iomanip>
#include <mutex>
#include <cctype>

namespace gazebo
{
class SimpleDronePlugin : public ModelPlugin
{
  struct CachedFrame
  {
    std::vector<unsigned char> data;
    unsigned int width = 0;
    unsigned int height = 0;
    unsigned int depth = 0;
    std::string format;
    common::Time time;
  };

public:
  void Load(physics::ModelPtr model, sdf::ElementPtr sdf) override
  {
    this->model = model;
    this->world = model->GetWorld();

    this->speed = 0.6;
    if (sdf->HasElement("speed"))
      this->speed = sdf->Get<double>("speed");

    // Where to save the captured RGB frames. The run script sets this env var
    // so the model can be reused without hardcoded project paths.
    const char *envImageDir = std::getenv("SIMPLE_DRONE_IMAGE_DIR");
    if (envImageDir && envImageDir[0] != '\0')
    {
      this->imageDir = envImageDir;
    }
    else if (sdf->HasElement("image_dir"))
    {
      this->imageDir = sdf->Get<std::string>("image_dir");
    }
    else
    {
      this->imageDir = "drone_images";
    }

    // (Legacy <capture_period> is ignored: frames are now captured once per
    // waypoint, on arrival, rather than on a fixed time interval.)
    this->capturePeriod = 1.0;
    if (sdf->HasElement("capture_period"))
      this->capturePeriod = sdf->Get<double>("capture_period");

    this->datasetMode = false;
    this->quitOnFinish = false;
    this->rejectGrayImages = true;
    this->grayDelta = this->EnvInt("SIMPLE_DRONE_GRAY_DELTA", 3);
    this->grayMin = this->EnvInt("SIMPLE_DRONE_GRAY_MIN", 120);
    this->grayMax = this->EnvInt("SIMPLE_DRONE_GRAY_MAX", 136);
    this->grayMaxRatio = std::min(
      0.99, std::max(0.0, this->EnvDouble("SIMPLE_DRONE_GRAY_MAX_RATIO", 0.12)));
    this->grayTileRatio = std::min(
      0.99, std::max(0.0, this->EnvDouble("SIMPLE_DRONE_GRAY_TILE_RATIO", 0.90)));
    this->grayScanlineRatio = std::min(
      0.99, std::max(0.0, this->EnvDouble("SIMPLE_DRONE_GRAY_SCANLINE_RATIO", 0.95)));
    this->minLumaStd = this->EnvDouble("SIMPLE_DRONE_MIN_LUMA_STD", 4.0);
    this->minRgbRange = this->EnvInt("SIMPLE_DRONE_MIN_RGB_RANGE", 12);
    this->viewDownTilt = this->EnvDouble("SIMPLE_DRONE_VIEW_DOWN_TILT", 0.55);
    this->minValidImageRatio =
      this->EnvDouble("SIMPLE_DRONE_MIN_VALID_IMAGE_RATIO", 0.001);
    const char *envRejectGrayImages = std::getenv("SIMPLE_DRONE_REJECT_GRAY_IMAGES");
    if (envRejectGrayImages && std::string(envRejectGrayImages) == "0")
      this->rejectGrayImages = false;

    const char *envQuitOnFinish = std::getenv("SIMPLE_DRONE_QUIT_ON_FINISH");
    if (envQuitOnFinish && envQuitOnFinish[0] != '\0' &&
        std::string(envQuitOnFinish) != "0")
      this->quitOnFinish = true;
    const char *envDoneFile = std::getenv("SIMPLE_DRONE_DONE_FILE");
    if (envDoneFile && envDoneFile[0] != '\0')
      this->doneFile = envDoneFile;

    const char *envDatasetRoot = std::getenv("SIMPLE_DRONE_DATASET_ROOT");
    if (envDatasetRoot && envDatasetRoot[0] != '\0')
    {
      this->datasetRoot = envDatasetRoot;
      this->datasetMode = true;
    }
    const char *envDatasetTrajectoryFile =
      std::getenv("SIMPLE_DRONE_DATASET_TRAJECTORY_FILE");
    if (envDatasetTrajectoryFile && envDatasetTrajectoryFile[0] != '\0')
      this->datasetTrajectoryFile = envDatasetTrajectoryFile;

    // The four viewpoints we want to read. The names must match the
    // <sensor> names declared in the model SDF.
    this->cameraNames = {"cam_front", "cam_down", "cam_left", "cam_right"};
    // Output sub-folder for each viewpoint (decoupled from the sensor name,
    // so e.g. cam_front is saved under <image_dir>/front/).
    this->folderNames = this->datasetMode
      ? std::vector<std::string>{"images_front", "images_down", "images_left", "images_right"}
      : std::vector<std::string>{"front", "down", "left", "right"};
    this->cameras.resize(this->cameraNames.size());
    this->imageConnections.resize(this->cameraNames.size());
    this->latestFrames.resize(this->cameraNames.size());

    if (this->datasetMode)
    {
      boost::filesystem::create_directories(this->imageDir);
      gzmsg << "[SimpleDronePlugin] saving dataset RGB frames under: "
            << this->imageDir
            << "/<trajectory>/{images_front,images_down,images_left,images_right}/"
            << std::endl;
    }
    else
    {
      // Each viewpoint gets its own sub-folder, e.g. <image_dir>/front/.
      for (const std::string &name : this->folderNames)
        boost::filesystem::create_directories(this->imageDir + "/" + name);
      gzmsg << "[SimpleDronePlugin] saving RGB frames under: "
            << this->imageDir << "/{" ;
      for (size_t i = 0; i < this->folderNames.size(); ++i)
        gzmsg << this->folderNames[i]
              << (i + 1 < this->folderNames.size() ? "," : "}/\n");
    }

    if (!this->datasetMode)
    {
      // Trajectory log: one row per saved frame set (one per waypoint). The
      // `frame` column matches both the image filename and the waypoint index,
      // e.g. frame 5 <-> front/000005.png <-> waypoints[5].
      const std::string trajPath = this->imageDir + "/trajectory.csv";
      this->trajFile.open(trajPath, std::ios::out | std::ios::trunc);
      this->trajFile << "frame,sim_time,x,y,z,"
                        "roll_rad,pitch_rad,yaw_rad,roll_deg,pitch_deg,yaw_deg,"
                        "qw,qx,qy,qz\n";
      gzmsg << "[SimpleDronePlugin] saving trajectory to: " << trajPath << std::endl;
    }

    if (this->rejectGrayImages)
    {
      gzmsg << "[SimpleDronePlugin] gray-frame rejection enabled: "
            << "gray_delta=" << this->grayDelta
            << ", gray_range=[" << this->grayMin << ',' << this->grayMax << ']'
            << ", max_gray_ratio=" << this->grayMaxRatio
            << ", max_gray_tile_ratio=" << this->grayTileRatio
            << ", max_gray_scanline_ratio=" << this->grayScanlineRatio
            << ", min_luma_std=" << this->minLumaStd
            << ", min_rgb_range=" << this->minRgbRange
            << std::endl;
    }

    this->camerasReady = false;
    this->frameCounter = 0;
    this->commandMode = false;
    this->waitingForCommand = false;
    this->commandYaw = 0.0;

    const char *envCommandFile = std::getenv("SIMPLE_DRONE_COMMAND_FILE");
    if (envCommandFile && envCommandFile[0] != '\0')
    {
      this->commandFile = envCommandFile;
      this->commandMode = true;
    }
    else if (sdf->HasElement("command_file"))
    {
      this->commandFile = sdf->Get<std::string>("command_file");
      this->commandMode = !this->commandFile.empty();
    }

    this->lastCommandMTime = 0;
    if (this->commandMode)
    {
      if (boost::filesystem::exists(this->commandFile))
      {
        this->lastCommandMTime = boost::filesystem::last_write_time(this->commandFile);
        std::ifstream existing(this->commandFile);
        std::ostringstream buf;
        buf << existing.rdbuf();
        this->lastCommandText = buf.str();
      }
      gzmsg << "[SimpleDronePlugin] command mode enabled; waiting for: "
            << this->commandFile << std::endl;
    }

    // Capture happens once per waypoint. Begin in the "settling" state on
    // waypoints[0] (the takeoff/start point): the drone is pinned to the exact
    // waypoint and we wait for the cameras to render a fresh frame from that
    // pose before saving, so the first image+row are the start point and every
    // saved image corresponds to its logged coordinate (not one render earlier).
    this->settling = true;
    this->settleBaselineSet = false;
    this->captureFailureWarned = false;
    this->settleTimeoutWarned = false;
    this->captureYaw = 0.0;
    this->grayRejectWarnCounter = 0;
    this->sweepInProgress = false;
    this->sweepPoseSet = false;
    this->sweepViewIndex = 0;
    this->sweepYawAttempt = 0;
    this->sweepTimeoutWarned = false;
    this->physicalSequenceInProgress = false;
    this->physicalViewIndex = 0;
    this->physicalWarned = false;
    this->physicalViewArmed = false;
    this->physicalBaselineTime = common::Time::Zero;
    this->physicalRejectCount = 0;
    this->physicalFallbackToSweep = false;

    this->returningToStart = false;
    this->currentDatasetTrajectory = 0;

    if (this->datasetMode)
    {
      this->trajectoryDir = this->datasetRoot + "/trajectory";
      this->LoadDatasetTrajectories();
    }

    // Tour of the whole 15x10 apartment. Safe envelope: x in [-6.5,6.5],
    // y in [-4,4], z in [1.2,1.8] (clear of walls, furniture and ceiling).
    // Order: center -> dining -> living -> TV/kitchen front -> bedroom -> back.
    if (this->datasetMode)
    {
      if (!this->BeginDatasetTrajectory(0))
      {
        gzerr << "[SimpleDronePlugin] no dataset trajectories loaded from "
              << this->trajectoryDir << std::endl;
      }
    }
    else
    {
      this->waypoints.push_back(ignition::math::Vector3d(-7.0,  0.6, 1.8)); // takeoff: clear strip on left wall, yaw=0 (+x), overview of whole apartment
    }
    if (!this->commandMode && !this->datasetMode)
    {
      this->waypoints.push_back(ignition::math::Vector3d(-4.5,  -3.0, 1.6));  // dining area
      this->waypoints.push_back(ignition::math::Vector3d(-5.8,  0.0, 1.4));  // living-room corner
      this->waypoints.push_back(ignition::math::Vector3d(-4.4, 3.3, 1.7));  // sofa / TV wall
      this->waypoints.push_back(ignition::math::Vector3d( 0.0, 3.5, 1.5));  // sweep along front wall
      this->waypoints.push_back(ignition::math::Vector3d( 4.0, 3.3, 1.4));  // kitchen
      this->waypoints.push_back(ignition::math::Vector3d( 5.8,  0.0, 1.6));  // toward bedroom
      this->waypoints.push_back(ignition::math::Vector3d( 4.8,  -3.0, 1.7));  // bed / wardrobe
      this->waypoints.push_back(ignition::math::Vector3d( 0.0,  -3.5, 1.5));  // back wall windows
      this->waypoints.push_back(ignition::math::Vector3d( 0.0,  0.0, 1.3));  // back to center
    }

    this->targetIndex = 0;
    this->tourComplete = false;
    this->lastTime = this->world->SimTime();

    this->updateConnection = event::Events::ConnectWorldUpdateBegin(
      std::bind(&SimpleDronePlugin::OnUpdate, this));
  }

private:
  // Look up the four camera sensors by name. Sensors are created after the
  // model is loaded, so this is retried each update until all are found.
  bool InitCameras()
  {
    sensors::SensorManager *mgr = sensors::SensorManager::Instance();
    if (!mgr || !mgr->SensorsInitialized())
      return false;

    bool allFound = true;
    for (size_t i = 0; i < this->cameraNames.size(); ++i)
    {
      if (this->cameras[i])
        continue;

      sensors::SensorPtr s = mgr->GetSensor(this->cameraNames[i]);
      sensors::CameraSensorPtr cam =
        std::dynamic_pointer_cast<sensors::CameraSensor>(s);

      if (cam)
      {
        cam->SetActive(true);
        // Make sure the rendering camera keeps a CPU-side copy of the frame
        // so we can read the RGB bytes / save them.
        if (cam->Camera())
        {
          cam->Camera()->SetCaptureData(true);
          this->imageConnections[i] = cam->Camera()->ConnectNewImageFrame(
            [this, i](const unsigned char *image,
                      unsigned int width,
                      unsigned int height,
                      unsigned int depth,
                      const std::string &format)
            {
              if (!image || width == 0 || height == 0 || depth == 0)
                return;
              CachedFrame frame;
              frame.width = width;
              frame.height = height;
              frame.depth = depth;
              frame.format = format;
              frame.time = this->world ? this->world->SimTime() : common::Time::Zero;
              const size_t bytes =
                static_cast<size_t>(width) * static_cast<size_t>(height) * depth;
              frame.data.assign(image, image + bytes);

              std::lock_guard<std::mutex> lock(this->frameMutex);
              if (i < this->latestFrames.size())
                this->latestFrames[i] = std::move(frame);
            });
        }
        cam->Update(true);
        this->cameras[i] = cam;
      }
      else
      {
        allFound = false;
      }
    }
    return allFound;
  }

  ignition::math::Vector3d RotateYaw(
      const ignition::math::Vector3d &v,
      const double yaw) const
  {
    const double c = std::cos(yaw);
    const double s = std::sin(yaw);
    return ignition::math::Vector3d(
      c * v.X() - s * v.Y(),
      s * v.X() + c * v.Y(),
      v.Z());
  }

  ignition::math::Pose3d ViewPose(
      const ignition::math::Pose3d &base,
      const size_t viewIndex) const
  {
    const ignition::math::Vector3d &p = base.Pos();
    const double yaw = base.Rot().Yaw();
    ignition::math::Vector3d offset;
    double roll = this->viewDownTilt;
    double pitch = 0.0;
    double viewYaw = yaw;

    if (viewIndex == 0)  // front
    {
      offset = this->RotateYaw(ignition::math::Vector3d(0.62, 0.0, 0.0), yaw);
      viewYaw = yaw;
    }
    else if (viewIndex == 1)  // down
    {
      offset = ignition::math::Vector3d(0.0, 0.0, -0.35);
      pitch = ignition::math::Angle::HalfPi.Radian();
      viewYaw = yaw;
    }
    else if (viewIndex == 2)  // left
    {
      offset = this->RotateYaw(ignition::math::Vector3d(0.0, 0.62, 0.0), yaw);
      viewYaw = yaw + ignition::math::Angle::HalfPi.Radian();
    }
    else  // right
    {
      offset = this->RotateYaw(ignition::math::Vector3d(0.0, -0.62, 0.0), yaw);
      viewYaw = yaw - ignition::math::Angle::HalfPi.Radian();
    }

    return ignition::math::Pose3d(
      p.X() + offset.X(),
      p.Y() + offset.Y(),
      p.Z() + offset.Z(),
      roll,
      pitch,
      viewYaw);
  }

  ignition::math::Pose3d SweepModelPose(
      const ignition::math::Pose3d &base,
      const size_t viewIndex,
      const double yawOffset = 0.0) const
  {
    const ignition::math::Vector3d &p = base.Pos();
    const double yaw = base.Rot().Yaw();
    double roll = 0.0;
    double pitch = 0.0;
    double viewYaw = yaw;

    // cam_right looks along the model's right side. Rotate the model in place
    // so that one known-good physical camera provides all required views.
    if (viewIndex == 0)        // front
      viewYaw = yaw + ignition::math::Angle::HalfPi.Radian();
    else if (viewIndex == 1)   // down
      roll = ignition::math::Angle::HalfPi.Radian();
    else if (viewIndex == 2)   // left
      viewYaw = yaw + M_PI;
    else                       // right
      viewYaw = yaw;
    viewYaw += yawOffset;

    return ignition::math::Pose3d(
      p.X(), p.Y(), p.Z(),
      roll, pitch, viewYaw);
  }

  bool RenderViewFrames(
      const ignition::math::Pose3d &basePose,
      std::vector<CachedFrame> &frames)
  {
    if (this->cameras.empty())
      return false;

    // Use cam_right as the capture source. On the target machine this is the
    // only physical camera that consistently produces scene pixels; rotating
    // the model in place is stable, while moving the Ogre camera directly can
    // segfault in gzserver.
    const size_t sourceIndex = std::min<size_t>(3u, this->cameras.size() - 1u);
    sensors::CameraSensorPtr sensor = this->cameras[sourceIndex];
    if (!sensor || !sensor->Camera())
      return false;

    rendering::CameraPtr renderCam = sensor->Camera();
    renderCam->SetCaptureData(true);
    sensor->SetActive(true);
    frames.assign(this->cameraNames.size(), CachedFrame());

    for (size_t i = 0; i < this->cameraNames.size(); ++i)
    {
      const ignition::math::Pose3d pose = this->SweepModelPose(basePose, i);
      this->model->SetWorldPose(pose);
      this->model->SetLinearVel(ignition::math::Vector3d::Zero);
      sensor->Update(true);

      const unsigned char *data = renderCam->ImageData();
      const unsigned int width = renderCam->ImageWidth();
      const unsigned int height = renderCam->ImageHeight();
      const unsigned int depth = renderCam->ImageDepth();
      if (!data || width == 0 || height == 0 || depth < 3)
      {
        if (!this->captureFailureWarned)
        {
          gzerr << "[SimpleDronePlugin] movable render camera not ready for "
                << this->cameraNames[i]
                << "; width=" << width
                << ", height=" << height
                << ", depth=" << depth << std::endl;
          this->captureFailureWarned = true;
        }
        return false;
      }

      CachedFrame frame;
      frame.width = width;
      frame.height = height;
      frame.depth = depth;
      frame.format = renderCam->ImageFormat();
      frame.time = this->world ? this->world->SimTime() : common::Time::Zero;
      const size_t bytes =
        static_cast<size_t>(width) * static_cast<size_t>(height) * depth;
      frame.data.assign(data, data + bytes);
      frames[i] = std::move(frame);
    }

    this->model->SetWorldPose(basePose);
    this->model->SetLinearVel(ignition::math::Vector3d::Zero);

    return true;
  }

  void ResetSingleCameraSweep()
  {
    if (this->sweepInProgress)
    {
      this->model->SetWorldPose(this->sweepBasePose);
      this->model->SetLinearVel(ignition::math::Vector3d::Zero);
    }
    this->sweepInProgress = false;
    this->sweepPoseSet = false;
    this->sweepViewIndex = 0;
    this->sweepYawAttempt = 0;
    this->sweepFrames.clear();
    this->sweepTimeoutWarned = false;
  }

  bool CropGrayBackground(CachedFrame &frame) const
  {
    if (frame.data.empty() || frame.width == 0 || frame.height == 0 ||
        frame.depth != 3)
      return false;

    unsigned int minX = frame.width;
    unsigned int minY = frame.height;
    unsigned int maxX = 0;
    unsigned int maxY = 0;
    size_t validPixels = 0;

    for (unsigned int y = 0; y < frame.height; ++y)
    {
      for (unsigned int x = 0; x < frame.width; ++x)
      {
        const size_t offset =
          (static_cast<size_t>(y) * frame.width + x) * frame.depth;
        const bool isGazeboGray =
          frame.data[offset] == 128 &&
          frame.data[offset + 1] == 128 &&
          frame.data[offset + 2] == 128;
        if (!isGazeboGray)
        {
          minX = std::min(minX, x);
          minY = std::min(minY, y);
          maxX = std::max(maxX, x);
          maxY = std::max(maxY, y);
          ++validPixels;
        }
      }
    }

    const size_t totalPixels =
      static_cast<size_t>(frame.width) * static_cast<size_t>(frame.height);
    const double validRatio =
      static_cast<double>(validPixels) / std::max<size_t>(totalPixels, 1u);
    if (validRatio < this->minValidImageRatio || minX > maxX || minY > maxY)
      return false;

    const unsigned int margin = 4;
    minX = minX > margin ? minX - margin : 0;
    minY = minY > margin ? minY - margin : 0;
    maxX = std::min(frame.width - 1, maxX + margin);
    maxY = std::min(frame.height - 1, maxY + margin);

    const unsigned int cropW = maxX - minX + 1;
    const unsigned int cropH = maxY - minY + 1;
    if (cropW < 4 || cropH < 4)
      return false;

    std::vector<unsigned char> resized(
      static_cast<size_t>(frame.width) * frame.height * 3u);
    for (unsigned int y = 0; y < frame.height; ++y)
    {
      const unsigned int srcY =
        minY + std::min(cropH - 1,
                        static_cast<unsigned int>(
                          (static_cast<unsigned long long>(y) * cropH) /
                          frame.height));
      for (unsigned int x = 0; x < frame.width; ++x)
      {
        const unsigned int srcX =
          minX + std::min(cropW - 1,
                          static_cast<unsigned int>(
                            (static_cast<unsigned long long>(x) * cropW) /
                            frame.width));
        const size_t src =
          (static_cast<size_t>(srcY) * frame.width + srcX) * 3u;
        const size_t dst =
          (static_cast<size_t>(y) * frame.width + x) * 3u;
        resized[dst] = frame.data[src];
        resized[dst + 1] = frame.data[src + 1];
        resized[dst + 2] = frame.data[src + 2];
      }
    }

    unsigned long long sumR = 0;
    unsigned long long sumG = 0;
    unsigned long long sumB = 0;
    size_t fillSourcePixels = 0;
    for (size_t i = 0; i + 2 < resized.size(); i += 3)
    {
      const bool isGazeboGray =
        resized[i] == 128 && resized[i + 1] == 128 && resized[i + 2] == 128;
      if (!isGazeboGray)
      {
        sumR += resized[i];
        sumG += resized[i + 1];
        sumB += resized[i + 2];
        ++fillSourcePixels;
      }
    }
    if (fillSourcePixels == 0)
      return false;
    const unsigned char fillR =
      static_cast<unsigned char>(sumR / fillSourcePixels);
    const unsigned char fillG =
      static_cast<unsigned char>(sumG / fillSourcePixels);
    const unsigned char fillB =
      static_cast<unsigned char>(sumB / fillSourcePixels);
    for (size_t i = 0; i + 2 < resized.size(); i += 3)
    {
      const bool isGazeboGray =
        resized[i] == 128 && resized[i + 1] == 128 && resized[i + 2] == 128;
      if (isGazeboGray)
      {
        resized[i] = fillR;
        resized[i + 1] = fillG;
        resized[i + 2] = fillB;
      }
    }

    frame.data.swap(resized);
    return true;
  }

  bool NormalizeFrameToRgb(
      const CachedFrame &src,
      CachedFrame &dst) const
  {
    if (src.data.empty() || src.width == 0 || src.height == 0 || src.depth < 3)
      return false;

    std::string format = src.format;
    std::transform(format.begin(), format.end(), format.begin(),
                   [](unsigned char c) { return static_cast<char>(std::tolower(c)); });
    const bool bgr =
      format.find("b8g8r8") != std::string::npos ||
      format.find("bgr") != std::string::npos;

    const size_t pixelCount =
      static_cast<size_t>(src.width) * static_cast<size_t>(src.height);
    dst.data.resize(pixelCount * 3u);
    dst.width = src.width;
    dst.height = src.height;
    dst.depth = 3;
    dst.format = "R8G8B8";
    dst.time = src.time;

    for (size_t i = 0; i < pixelCount; ++i)
    {
      const size_t in = i * src.depth;
      const size_t out = i * 3u;
      if (bgr)
      {
        dst.data[out] = src.data[in + 2];
        dst.data[out + 1] = src.data[in + 1];
        dst.data[out + 2] = src.data[in];
      }
      else
      {
        dst.data[out] = src.data[in];
        dst.data[out + 1] = src.data[in + 1];
        dst.data[out + 2] = src.data[in + 2];
      }
    }

    return true;
  }

  bool AdvanceSingleCameraSweep(std::vector<CachedFrame> &frames)
  {
    if (this->cameras.empty())
      return false;

    const size_t sourceIndex = std::min<size_t>(3u, this->cameras.size() - 1u);
    sensors::CameraSensorPtr sensor = this->cameras[sourceIndex];
    if (!sensor || !sensor->Camera())
      return false;

    if (!this->sweepInProgress)
    {
      this->sweepBasePose = this->model->WorldPose();
      this->sweepFrames.assign(this->cameraNames.size(), CachedFrame());
      this->sweepViewIndex = 0;
      this->sweepPoseSet = false;
      this->sweepInProgress = true;
      this->sweepStartTime = this->world ? this->world->SimTime() : common::Time::Zero;
      this->sweepTimeoutWarned = false;
    }

    if (this->sweepViewIndex >= this->cameraNames.size())
    {
      frames = this->sweepFrames;
      this->ResetSingleCameraSweep();
      return true;
    }

    sensor->SetActive(true);
    sensor->Camera()->SetCaptureData(true);

    const double yawOffset =
      static_cast<double>(this->sweepYawAttempt) *
      ignition::math::Angle::HalfPi.Radian() * 0.5;
    const ignition::math::Pose3d pose =
      this->SweepModelPose(this->sweepBasePose, this->sweepViewIndex, yawOffset);
    this->model->SetWorldPose(pose);
    this->model->SetLinearVel(ignition::math::Vector3d::Zero);

    if (!this->sweepPoseSet)
    {
      {
        std::lock_guard<std::mutex> lock(this->frameMutex);
        this->sweepBaselineFrameTime =
          sourceIndex < this->latestFrames.size()
            ? this->latestFrames[sourceIndex].time
            : common::Time::Zero;
      }
      sensor->Update(true);
      this->sweepPoseSet = true;
      return false;
    }

    sensor->Update(true);

    CachedFrame sourceFrame;
    {
      std::lock_guard<std::mutex> lock(this->frameMutex);
      if (sourceIndex < this->latestFrames.size())
        sourceFrame = this->latestFrames[sourceIndex];
    }

    if (sourceFrame.data.empty() ||
        sourceFrame.time <= this->sweepBaselineFrameTime)
    {
      const common::Time now = this->world ? this->world->SimTime() : common::Time::Zero;
      const double wait = (now - this->sweepStartTime).Double();
      if (wait > this->settleTimeout && !this->sweepTimeoutWarned)
      {
        gzerr << "[SimpleDronePlugin] camera sweep timeout at target index "
              << this->targetIndex << "; view=" << this->cameraNames[this->sweepViewIndex]
              << ". Waiting for a fresh frame." << std::endl;
        this->sweepTimeoutWarned = true;
      }
      return false;
    }

    CachedFrame rgbFrame;
    if (!this->NormalizeFrameToRgb(sourceFrame, rgbFrame))
      return false;
    if (!this->CropGrayBackground(rgbFrame))
    {
      ++this->sweepYawAttempt;
      this->sweepPoseSet = false;
      if (this->sweepYawAttempt <= 8)
        return false;

      gzerr << "[SimpleDronePlugin] unable to find non-gray content at target index "
            << this->targetIndex << "; view="
            << this->cameraNames[this->sweepViewIndex] << std::endl;
      this->sweepYawAttempt = 0;
      return false;
    }

    this->sweepFrames[this->sweepViewIndex] = std::move(rgbFrame);
    ++this->sweepViewIndex;
    this->sweepYawAttempt = 0;
    this->sweepPoseSet = false;

    if (this->sweepViewIndex < this->cameraNames.size())
      return false;

    frames = this->sweepFrames;
    this->ResetSingleCameraSweep();
    return true;
  }

  bool ReadPhysicalCameraFrames(std::vector<CachedFrame> &frames)
  {
    std::lock_guard<std::mutex> lock(this->frameMutex);
    frames = this->latestFrames;
    return frames.size() == this->cameraNames.size();
  }

  void ResetPhysicalCameraSequence()
  {
    this->physicalSequenceInProgress = false;
    this->physicalViewIndex = 0;
    this->physicalWarned = false;
    this->physicalViewArmed = false;
    this->physicalBaselineTime = common::Time::Zero;
    this->physicalFrames.clear();
  }

  bool AdvancePhysicalCameraSequence(std::vector<CachedFrame> &frames)
  {
    if (!this->physicalSequenceInProgress)
    {
      this->physicalSequenceInProgress = true;
      this->physicalViewIndex = 0;
      this->physicalWarned = false;
      this->physicalViewArmed = false;
      this->physicalBaselineTime = common::Time::Zero;
      this->physicalFrames.assign(this->cameraNames.size(), CachedFrame());
    }

    if (this->physicalViewIndex >= this->cameraNames.size())
    {
      frames = this->physicalFrames;
      this->ResetPhysicalCameraSequence();
      return true;
    }

    for (size_t i = 0; i < this->cameras.size(); ++i)
    {
      if (!this->cameras[i])
        continue;
      this->cameras[i]->SetActive(i == this->physicalViewIndex);
      if (this->cameras[i]->Camera())
        this->cameras[i]->Camera()->SetCaptureData(i == this->physicalViewIndex);
      if (i == this->physicalViewIndex)
        this->cameras[i]->Update(true);
    }

    if (!this->physicalViewArmed)
    {
      std::lock_guard<std::mutex> lock(this->frameMutex);
      if (this->physicalViewIndex < this->latestFrames.size())
        this->physicalBaselineTime = this->latestFrames[this->physicalViewIndex].time;
      else
        this->physicalBaselineTime = common::Time::Zero;
      this->physicalViewArmed = true;
      return false;
    }

    CachedFrame candidate;
    {
      std::lock_guard<std::mutex> lock(this->frameMutex);
      if (this->physicalViewIndex >= this->latestFrames.size())
        return false;
      candidate = this->latestFrames[this->physicalViewIndex];
    }

    if (candidate.time <= this->physicalBaselineTime)
      return false;

    if (candidate.data.empty() || candidate.width == 0 ||
        candidate.height == 0 || candidate.depth < 3)
      return false;

    std::string reason;
    if (!this->FrameLooksUsable(
          candidate.data.data(),
          candidate.width,
          candidate.height,
          candidate.depth,
          reason))
    {
      if (!this->physicalWarned)
      {
        gzerr << "[SimpleDronePlugin] waiting for usable physical camera frame at target index "
              << this->targetIndex << "; camera="
              << this->cameraNames[this->physicalViewIndex]
              << "; " << reason << std::endl;
        this->physicalWarned = true;
      }
      this->physicalBaselineTime = candidate.time;
      ++this->physicalRejectCount;
      if (this->physicalRejectCount >= 60)
      {
        gzerr << "[SimpleDronePlugin] physical cameras stayed unusable at target index "
              << this->targetIndex
              << "; switching the remainder of this trajectory to single-camera sweep."
              << std::endl;
        this->physicalFallbackToSweep = true;
        this->ResetPhysicalCameraSequence();
      }
      return false;
    }

    this->physicalFrames[this->physicalViewIndex] = std::move(candidate);
    ++this->physicalViewIndex;
    this->physicalWarned = false;
    this->physicalViewArmed = false;
    this->physicalBaselineTime = common::Time::Zero;
    return false;
  }

  // Read the latest RGB frame from each camera and write it to disk as PNG.
  // Returns true only when a complete frame set is written, so images and
  // trajectory rows stay in one-to-one correspondence (sharing one frame index).
  bool CaptureFrames()
  {
    // Capture only once EVERY camera has a rendered frame this tick. During the
    // first few updates the render pipeline is still warming up and ImageData()
    // is null; capturing then would advance the frame counter and log a
    // trajectory row with no PNG on disk, breaking the image<->trajectory
    // pairing. Bail out so this frame index is retried until all views render.
    std::vector<CachedFrame> frames;
    const char *singleCameraSweep = std::getenv("SIMPLE_DRONE_SINGLE_CAMERA_SWEEP");
    const bool useSingleCameraSweep =
      this->physicalFallbackToSweep ||
      (singleCameraSweep && std::string(singleCameraSweep) != "0");
    if (useSingleCameraSweep)
    {
      if (!this->AdvanceSingleCameraSweep(frames))
        return false;
    }
    else
    {
      if (!this->AdvancePhysicalCameraSequence(frames))
        return false;
    }

    for (size_t i = 0; i < this->cameras.size(); ++i)
    {
      if (i >= frames.size() || frames[i].data.empty() ||
          frames[i].width == 0 || frames[i].height == 0 || frames[i].depth < 3)
      {
        if (!this->captureFailureWarned)
        {
          gzerr << "[SimpleDronePlugin] camera frame not ready at target index "
                << this->targetIndex << "; camera=" << this->cameraNames[i]
                << ", movable_frame=" << (i < frames.size() && !frames[i].data.empty())
                << std::endl;
          this->captureFailureWarned = true;
        }
        return false;
      }
    }

    std::string frameName;
    if (this->datasetMode && this->currentDatasetTrajectory < this->datasetTrajectories.size())
    {
      const DatasetTrajectory &traj = this->datasetTrajectories[this->currentDatasetTrajectory];
      const DatasetPoint &pt = traj.points[this->targetIndex];
      std::ostringstream name;
      name << traj.name << "_step_" << std::setw(6) << std::setfill('0') << pt.step << ".png";
      frameName = name.str();
    }

    if (this->rejectGrayImages)
    {
      for (size_t i = 0; i < this->cameras.size(); ++i)
      {
        const CachedFrame &frame = frames[i];
        const unsigned char *data = frame.data.data();
        std::string reason;
        if (!this->FrameLooksUsable(
              data,
              frame.width,
              frame.height,
              frame.depth,
              reason))
        {
          if (this->grayRejectWarnCounter % 100 == 0)
          {
            gzerr << "[SimpleDronePlugin] rejected gray/unusable frame at target index "
                  << this->targetIndex << "; camera=" << this->cameraNames[i]
                  << "; " << reason << ". Waiting for a new frame." << std::endl;
          }
          ++this->grayRejectWarnCounter;
          if (useSingleCameraSweep)
            this->ResetSingleCameraSweep();
          else
            this->ResetPhysicalCameraSequence();
          return false;
        }
      }
    }

    // All four views are ready -- save them under the shared frame index.
    for (size_t i = 0; i < this->cameras.size(); ++i)
    {
      const CachedFrame &frame = frames[i];
      // `cam->ImageData()` is a tightly packed R8G8B8 buffer of size w * h * 3.
      // (Use it here directly if you want to feed it into an algorithm.)

      // ----- save the RGB image as PNG into this camera's sub-folder -----
      char name[300];
      if (this->datasetMode)
      {
        const DatasetTrajectory &traj =
          this->datasetTrajectories[this->currentDatasetTrajectory];
        std::snprintf(name, sizeof(name), "%s/%s/%s/%s",
                      this->imageDir.c_str(),
                      traj.name.c_str(),
                      this->folderNames[i].c_str(),
                      frameName.c_str());
      }
      else
      {
        std::snprintf(name, sizeof(name), "%s/%s/%06u.png",
                      this->imageDir.c_str(),
                      this->folderNames[i].c_str(),
                      this->frameCounter);
      }
      const unsigned char *data = frame.data.data();
      if (!data || frame.data.empty())
      {
        gzerr << "[SimpleDronePlugin] camera image data disappeared before save; camera="
              << this->cameraNames[i] << std::endl;
        return false;
      }
      const size_t pixelCount =
        static_cast<size_t>(frame.width) * static_cast<size_t>(frame.height) * 3u;
      unsigned int minValue = 255;
      unsigned int maxValue = 0;
      unsigned long long sumValue = 0;
      for (size_t pixel = 0; pixel < pixelCount; ++pixel)
      {
        const unsigned int value = static_cast<unsigned int>(data[pixel]);
        minValue = std::min(minValue, value);
        maxValue = std::max(maxValue, value);
        sumValue += value;
      }
      if (std::getenv("SIMPLE_DRONE_DEBUG_CAMERA"))
      {
        gzmsg << "[SimpleDronePlugin] camera buffer "
              << this->cameraNames[i]
              << " frame=" << this->frameCounter
              << " size=" << frame.width << "x" << frame.height
              << " min=" << minValue
              << " max=" << maxValue
              << " mean=" << (static_cast<double>(sumValue) / std::max<size_t>(pixelCount, 1u))
              << " first_rgb="
              << static_cast<unsigned int>(data[0]) << ','
              << static_cast<unsigned int>(data[1]) << ','
              << static_cast<unsigned int>(data[2])
              << std::endl;
      }
      common::Image image;
      image.SetFromData(
        data,
        frame.width,
        frame.height,
        common::Image::RGB_INT8);
      image.SavePNG(std::string(name));
    }

    // ----- log this trajectory point (3D position + orientation) -----
    ignition::math::Pose3d pose = this->model->WorldPose();
    const ignition::math::Vector3d &p = pose.Pos();
    const ignition::math::Quaterniond &q = pose.Rot();
    double roll = q.Roll();
    double pitch = q.Pitch();
    double yaw = q.Yaw();
    const double r2d = 180.0 / M_PI;
    double t = this->world->SimTime().Double();
    if (this->datasetMode && this->currentDatasetTrajectory < this->datasetTrajectories.size())
    {
      DatasetPoint &pt =
        this->datasetTrajectories[this->currentDatasetTrajectory].points[this->targetIndex];
      pt.capturedX = p.X();
      pt.capturedY = p.Y();
      pt.capturedZ = p.Z();
      pt.captureFrame = this->frameCounter;
      pt.capturedYawRad = yaw;
      pt.capturedYawDeg = yaw * r2d;
      pt.imageName = frameName;
      pt.captured = true;
    }
    else if (this->trajFile.is_open())
    {
      this->trajFile << this->frameCounter << ','
                     << t << ','
                     << p.X() << ',' << p.Y() << ',' << p.Z() << ','
                     << roll << ',' << pitch << ',' << yaw << ','
                     << (roll * r2d) << ',' << (pitch * r2d) << ',' << (yaw * r2d) << ','
                     << q.W() << ',' << q.X() << ',' << q.Y() << ',' << q.Z() << '\n';
      this->trajFile.flush();  // persist even if the sim is Ctrl+C'd
    }

    gzmsg << "[SimpleDronePlugin] saved frame set #"
          << this->frameCounter << " (front/down/left/right)" << std::endl;
    this->grayRejectWarnCounter = 0;
    this->physicalRejectCount = 0;
    ++this->frameCounter;
    return true;
  }

  void OnUpdate()
  {
    common::Time now = this->world->SimTime();

    // Tour finished: hold the drone at the final waypoint and record nothing.
    if (this->tourComplete)
    {
      this->model->SetWorldPose(this->holdPose);
      this->model->SetLinearVel(ignition::math::Vector3d::Zero);
      return;
    }

    // Lazily bind the cameras once the sensor manager has created them.
    if (!this->camerasReady)
      this->camerasReady = this->InitCameras();
    if (!this->camerasReady)
      return;  // nothing happens (no motion, no capture) until cameras exist

    if (this->waypoints.empty())
      return;

    // ===== settle-then-capture on each waypoint =====
    // While settling, the drone is pinned to the EXACT waypoint and we wait for
    // every camera to render a brand-new frame from that pinned pose before
    // saving. Gazebo renders the cameras *after* this callback, so without the
    // wait the saved PNG would be the frame rendered one step earlier (during
    // the approach, a few cm short). The wait makes each image truly correspond
    // to its logged coordinate. The start point (waypoints[0]) begins settling.
    if (this->settling)
    {
      const ignition::math::Vector3d &wp = this->waypoints[this->targetIndex];
      const ignition::math::Pose3d snapped(
        wp.X(), wp.Y(), wp.Z(), 0.0, 0.0,
        this->datasetMode ? 0.0 : this->captureYaw);
      this->model->SetWorldPose(snapped);  // re-assert every tick: hold dead still
      this->model->SetLinearVel(ignition::math::Vector3d::Zero);

      // First tick parked here: latch each camera's current render time as the
      // baseline, then yield so the cameras can render from the pinned pose.
      if (!this->settleBaselineSet)
      {
        this->baseRenderTime.resize(this->cameras.size());
        for (size_t i = 0; i < this->cameras.size(); ++i)
        {
          if (this->cameras[i])
          {
            this->cameras[i]->SetActive(true);
            this->cameras[i]->Update(true);
          }
          this->baseRenderTime[i] = this->cameras[i]
            ? this->cameras[i]->LastMeasurementTime() : common::Time::Zero;
        }
        this->settleStartTime = now;
        this->settleBaselineSet = true;
        this->captureFailureWarned = false;
        return;
      }

      // Hold until EVERY camera has produced a new frame strictly after the
      // snap (i.e. rendered from the pinned pose), then capture.
      bool allCamerasRerendered = true;
      for (size_t i = 0; i < this->cameras.size(); ++i)
      {
        if (this->cameras[i])
        {
          this->cameras[i]->SetActive(true);
          this->cameras[i]->Update(true);
        }
        if (!this->cameras[i] ||
            this->cameras[i]->LastMeasurementTime() <= this->baseRenderTime[i])
        {
          allCamerasRerendered = false;
          break;
        }
      }
      if (!allCamerasRerendered)
      {
        const double settleWait = (now - this->settleStartTime).Double();
        if (settleWait < this->settleTimeout)
          return;  // not all cameras have re-rendered yet -- keep waiting

        if (!this->settleTimeoutWarned)
        {
          gzerr << "[SimpleDronePlugin] camera settle timeout after "
                << settleWait << "s at target index " << this->targetIndex
                << "; capturing latest available frames." << std::endl;
          this->settleTimeoutWarned = true;
        }
      }

      if (!this->CaptureFrames())  // also guards against null image buffers
        return;

      this->settling = false;
      this->settleBaselineSet = false;
      this->captureFailureWarned = false;
      this->settleTimeoutWarned = false;
      this->ResetPhysicalCameraSequence();

      if (this->datasetMode)
      {
        this->settling = false;
        this->settleBaselineSet = false;
        this->captureFailureWarned = false;
        this->settleTimeoutWarned = false;
        this->AdvanceDatasetAfterCapture(snapped);
        return;
      }

      if (this->commandMode)
      {
        this->holdPose = snapped;
        this->waitingForCommand = true;
        this->lastTime = now;
        return;
      }

      // That was the last waypoint -> the single-pass tour is done.
      if (this->targetIndex + 1 >= this->waypoints.size())
      {
        this->FinishTour(snapped);
        return;
      }
      ++this->targetIndex;     // head for the next waypoint
      this->lastTime = now;    // keep the first travel dt to one step
      return;
    }

    if (this->commandMode && this->waitingForCommand)
    {
      this->model->SetWorldPose(this->holdPose);
      this->model->SetLinearVel(ignition::math::Vector3d::Zero);
      if (!this->TryLoadCommand())
        return;

      this->waypoints.resize(1);
      this->waypoints.push_back(this->commandTarget);
      this->targetIndex = 1;
      this->waitingForCommand = false;
      this->lastTime = now;
      return;
    }

    // ===== fly toward waypoints[targetIndex] =====
    double dt = (now - this->lastTime).Double();
    this->lastTime = now;
    if (dt <= 0.0)
      return;

    ignition::math::Vector3d pos = this->model->WorldPose().Pos();
    ignition::math::Vector3d diff = this->waypoints[this->targetIndex] - pos;

    if (diff.Length() < 0.08)
    {
      if (this->datasetMode && this->returningToStart)
      {
        size_t nextTrajectory = this->currentDatasetTrajectory + 1;
        if (!this->BeginDatasetTrajectoryAtStart(nextTrajectory))
        {
          this->FinishTour(this->model->WorldPose());
          return;
        }
        return;
      }

      // Arrived: latch the travel heading and start settling on the waypoint.
      if (this->datasetMode && this->currentDatasetTrajectory < this->datasetTrajectories.size())
        this->captureYaw = 0.0;
      else
      this->captureYaw = this->commandMode ? this->commandYaw
                                             : this->model->WorldPose().Rot().Yaw();
      this->settling = true;
      this->settleBaselineSet = false;
      this->captureFailureWarned = false;
      this->settleTimeoutWarned = false;
      return;
    }

    ignition::math::Vector3d dir = diff.Normalized();
    double yaw = this->datasetMode ? 0.0 : std::atan2(dir.Y(), dir.X());
    double travel = this->speed * dt;
    ignition::math::Vector3d newPos;
    if (travel >= diff.Length())
    {
      newPos = this->waypoints[this->targetIndex];
    }
    else
    {
      newPos = pos + dir * travel;
    }
    this->model->SetWorldPose(
      ignition::math::Pose3d(newPos.X(), newPos.Y(), newPos.Z(), 0.0, 0.0, yaw));
    this->model->SetLinearVel(travel >= diff.Length()
      ? ignition::math::Vector3d::Zero
      : dir * this->speed);
  }

  struct DatasetPoint
  {
    int step = 0;
    double x = 0.0;
    double y = 0.0;
    double z = 0.0;
    double yawRad = 0.0;
    double yawDeg = 0.0;
    double capturedX = 0.0;
    double capturedY = 0.0;
    double capturedZ = 0.0;
    unsigned int captureFrame = 0;
    double capturedYawRad = 0.0;
    double capturedYawDeg = 0.0;
    std::string imageName;
    bool captured = false;
  };

  int EnvInt(const char *name, int fallback)
  {
    const char *value = std::getenv(name);
    if (!value || value[0] == '\0')
      return fallback;
    try
    {
      return std::stoi(value);
    }
    catch (...)
    {
      return fallback;
    }
  }

  double EnvDouble(const char *name, double fallback)
  {
    const char *value = std::getenv(name);
    if (!value || value[0] == '\0')
      return fallback;
    try
    {
      return std::stod(value);
    }
    catch (...)
    {
      return fallback;
    }
  }

  bool FrameLooksUsable(
    const unsigned char *data,
    unsigned int width,
    unsigned int height,
    unsigned int depth,
    std::string &reason)
  {
    if (!data || width == 0 || height == 0 || depth < 3)
    {
      reason = "empty image buffer";
      return false;
    }

    const size_t pixelCount =
      static_cast<size_t>(width) * static_cast<size_t>(height);
    unsigned int globalMin = 255;
    unsigned int globalMax = 0;
    size_t grayPixels = 0;
    double lumaSum = 0.0;
    double lumaSqSum = 0.0;

    const unsigned int tilesX = 8;
    const unsigned int tilesY = 8;
    std::vector<size_t> tilePixels(tilesX * tilesY, 0);
    std::vector<size_t> tileGrayPixels(tilesX * tilesY, 0);
    std::vector<unsigned int> tileMin(tilesX * tilesY, 255);
    std::vector<unsigned int> tileMax(tilesX * tilesY, 0);
    std::vector<double> tileLumaSum(tilesX * tilesY, 0.0);
    std::vector<double> tileLumaSqSum(tilesX * tilesY, 0.0);
    std::vector<size_t> rowBufferPixels(height, 0);
    std::vector<size_t> columnBufferPixels(width, 0);

    for (unsigned int y = 0; y < height; ++y)
    {
      for (unsigned int x = 0; x < width; ++x)
      {
        const size_t offset =
          (static_cast<size_t>(y) * static_cast<size_t>(width) + x) * depth;
        const unsigned int r = static_cast<unsigned int>(data[offset]);
        const unsigned int g = static_cast<unsigned int>(data[offset + 1]);
        const unsigned int b = static_cast<unsigned int>(data[offset + 2]);
        const unsigned int cmin = std::min(r, std::min(g, b));
        const unsigned int cmax = std::max(r, std::max(g, b));
        const double luma = (static_cast<double>(r) + g + b) / 3.0;
        const unsigned int tileX = std::min((x * tilesX) / width, tilesX - 1);
        const unsigned int tileY = std::min((y * tilesY) / height, tilesY - 1);
        const size_t tileIndex = static_cast<size_t>(tileY) * tilesX + tileX;

        globalMin = std::min(globalMin, cmin);
        globalMax = std::max(globalMax, cmax);
        lumaSum += luma;
        lumaSqSum += luma * luma;
        ++tilePixels[tileIndex];
        tileMin[tileIndex] = std::min(tileMin[tileIndex], cmin);
        tileMax[tileIndex] = std::max(tileMax[tileIndex], cmax);
        tileLumaSum[tileIndex] += luma;
        tileLumaSqSum[tileIndex] += luma * luma;

        const bool isGray =
          (cmax - cmin <= static_cast<unsigned int>(this->grayDelta)) &&
          (luma >= this->grayMin) &&
          (luma <= this->grayMax);
        if (isGray)
        {
          ++grayPixels;
          ++tileGrayPixels[tileIndex];
        }
        if (r == 128u && g == 128u && b == 128u)
        {
          ++rowBufferPixels[y];
          ++columnBufferPixels[x];
        }
      }
    }

    const unsigned int rgbRange = globalMax - globalMin;
    const double mean = lumaSum / std::max<size_t>(pixelCount, 1u);
    const double variance =
      std::max(0.0, lumaSqSum / std::max<size_t>(pixelCount, 1u) - mean * mean);
    const double lumaStd = std::sqrt(variance);
    const double grayRatio =
      static_cast<double>(grayPixels) / std::max<size_t>(pixelCount, 1u);

    if (rgbRange < static_cast<unsigned int>(this->minRgbRange))
    {
      std::ostringstream out;
      out << "near-uniform image rgb_range=" << rgbRange
          << " luma_std=" << lumaStd;
      reason = out.str();
      return false;
    }

    if (grayRatio > this->grayMaxRatio)
    {
      std::ostringstream out;
      out << "global gray ratio too high ratio=" << grayRatio;
      reason = out.str();
      return false;
    }

    for (unsigned int y = 0; y < height; ++y)
    {
      const double ratio = static_cast<double>(rowBufferPixels[y]) / width;
      if (ratio > this->grayScanlineRatio)
      {
        std::ostringstream out;
        out << "gray render-buffer row ratio too high row=" << y
            << " ratio=" << ratio;
        reason = out.str();
        return false;
      }
    }
    for (unsigned int x = 0; x < width; ++x)
    {
      const double ratio = static_cast<double>(columnBufferPixels[x]) / height;
      if (ratio > this->grayScanlineRatio)
      {
        std::ostringstream out;
        out << "gray render-buffer column ratio too high column=" << x
            << " ratio=" << ratio;
        reason = out.str();
        return false;
      }
    }

    for (size_t i = 0; i < tilePixels.size(); ++i)
    {
      if (tilePixels[i] == 0)
        continue;
      const double tileRatio =
        static_cast<double>(tileGrayPixels[i]) / static_cast<double>(tilePixels[i]);
      const double tileMean =
        tileLumaSum[i] / static_cast<double>(tilePixels[i]);
      const double tileVariance =
        std::max(0.0,
                 tileLumaSqSum[i] / static_cast<double>(tilePixels[i]) -
                 tileMean * tileMean);
      const double tileStd = std::sqrt(tileVariance);
      const unsigned int tileRange = tileMax[i] - tileMin[i];
      if (tileRatio > this->grayTileRatio &&
          tileStd < this->minLumaStd &&
          tileRange < static_cast<unsigned int>(this->minRgbRange))
      {
        std::ostringstream out;
        out << "gray tile ratio too high tile=" << i
            << " ratio=" << tileRatio
            << " tile_range=" << tileRange
            << " tile_luma_std=" << tileStd;
        reason = out.str();
        return false;
      }
    }

    return true;
  }

  struct DatasetTrajectory
  {
    std::string name;
    std::string path;
    std::vector<DatasetPoint> points;
  };

  std::vector<std::string> SplitCsvLine(const std::string &line)
  {
    std::vector<std::string> cols;
    std::string col;
    std::istringstream ss(line);
    while (std::getline(ss, col, ','))
      cols.push_back(col);
    return cols;
  }

  void LoadDatasetTrajectories()
  {
    this->datasetTrajectories.clear();

    std::vector<std::string> csvFiles;
    if (!this->datasetTrajectoryFile.empty())
    {
      if (boost::filesystem::exists(this->datasetTrajectoryFile))
        csvFiles.push_back(this->datasetTrajectoryFile);
    }
    else
    {
      if (!boost::filesystem::exists(this->trajectoryDir))
        return;

      boost::filesystem::directory_iterator end;
      for (boost::filesystem::directory_iterator it(this->trajectoryDir); it != end; ++it)
      {
        if (boost::filesystem::is_regular_file(it->path()) && it->path().extension() == ".csv")
          csvFiles.push_back(it->path().string());
      }
      std::sort(csvFiles.begin(), csvFiles.end());
    }

    for (const std::string &path : csvFiles)
    {
      std::ifstream in(path);
      std::string line;
      if (!std::getline(in, line))
        continue;

      DatasetTrajectory traj;
      boost::filesystem::path p(path);
      traj.name = p.stem().string();
      traj.path = path;

      while (std::getline(in, line))
      {
        if (line.empty())
          continue;
        std::vector<std::string> cols = this->SplitCsvLine(line);
        if (cols.size() < 5)
          continue;

        DatasetPoint pt;
        try
        {
          pt.step = std::stoi(cols[0]);
          pt.x = std::stod(cols[1]);
          pt.y = std::stod(cols[2]);
          pt.z = std::stod(cols[3]);
          pt.yawRad = std::stod(cols[4]);
          pt.yawDeg = cols.size() > 5 ? std::stod(cols[5]) : pt.yawRad * 180.0 / M_PI;
        }
        catch (...)
        {
          continue;
        }
        traj.points.push_back(pt);
      }

      if (!traj.points.empty())
        this->datasetTrajectories.push_back(traj);
    }

    gzmsg << "[SimpleDronePlugin] loaded " << this->datasetTrajectories.size()
          << " dataset trajector"
          << (this->datasetTrajectories.size() == 1 ? "y" : "ies")
          << " from "
          << (this->datasetTrajectoryFile.empty()
                ? this->trajectoryDir
                : this->datasetTrajectoryFile)
          << std::endl;
  }

  bool BeginDatasetTrajectory(size_t index)
  {
    if (index >= this->datasetTrajectories.size())
      return false;

    this->currentDatasetTrajectory = index;
    this->waypoints.clear();
    const DatasetTrajectory &traj = this->datasetTrajectories[index];
    for (const DatasetPoint &pt : traj.points)
      this->waypoints.push_back(ignition::math::Vector3d(pt.x, pt.y, pt.z));

    this->targetIndex = 0;
    this->returningToStart = false;
    this->captureYaw = 0.0;
    this->settling = true;
    this->settleBaselineSet = false;
    this->captureFailureWarned = false;
    this->settleTimeoutWarned = false;
    this->physicalRejectCount = 0;
    this->physicalFallbackToSweep = false;
    this->lastTime = this->world->SimTime();
    gzmsg << "[SimpleDronePlugin] dataset trajectory "
          << (index + 1) << "/" << this->datasetTrajectories.size()
          << ": " << traj.name << " (" << traj.points.size()
          << " points)" << std::endl;

    for (const std::string &folder : this->folderNames)
      boost::filesystem::create_directories(this->imageDir + "/" + traj.name + "/" + folder);

    return true;
  }

  bool BeginDatasetTrajectoryAtStart(size_t index)
  {
    if (index >= this->datasetTrajectories.size())
      return false;

    const DatasetPoint &start = this->datasetTrajectories[index].points.front();
    this->model->SetWorldPose(
      ignition::math::Pose3d(start.x, start.y, start.z, 0.0, 0.0, 0.0));
    this->model->SetLinearVel(ignition::math::Vector3d::Zero);
    return this->BeginDatasetTrajectory(index);
  }

  void AdvanceDatasetAfterCapture(const ignition::math::Pose3d &snapped)
  {
    if (this->currentDatasetTrajectory >= this->datasetTrajectories.size())
      return;

    DatasetTrajectory &traj = this->datasetTrajectories[this->currentDatasetTrajectory];
    this->RewriteDatasetTrajectoryCsv(traj);

    if (this->targetIndex + 1 < traj.points.size())
    {
      ++this->targetIndex;
      this->captureYaw = 0.0;
      this->settling = true;
      this->settleBaselineSet = false;
      this->captureFailureWarned = false;
      this->settleTimeoutWarned = false;
      this->physicalRejectCount = 0;
      this->lastTime = this->world->SimTime();
      return;
    }

    this->FinishTour(snapped);
  }

  void RewriteDatasetTrajectoryCsv(const DatasetTrajectory &traj)
  {
    std::ofstream out(traj.path, std::ios::out | std::ios::trunc);
    out << "step,x,y,z,yaw_rad,yaw_deg,"
           "capture_frame,captured_yaw_rad,captured_yaw_deg,"
           "front_image,down_image,left_image,right_image\n";
    for (const DatasetPoint &pt : traj.points)
    {
      out << pt.step << ','
          << (pt.captured ? pt.capturedX : pt.x) << ','
          << (pt.captured ? pt.capturedY : pt.y) << ','
          << (pt.captured ? pt.capturedZ : pt.z) << ','
          << pt.yawRad << ','
          << pt.yawDeg << ',';
      if (pt.captured)
      {
        out << pt.captureFrame << ','
            << pt.capturedYawRad << ','
            << pt.capturedYawDeg << ','
            << pt.imageName << ','
            << pt.imageName << ','
            << pt.imageName << ','
            << pt.imageName << '\n';
      }
      else
      {
        out << ",,,,,,\n";
      }
    }
    out.flush();
    gzmsg << "[SimpleDronePlugin] updated dataset trajectory CSV: "
          << traj.path << std::endl;
  }

  bool TryLoadCommand()
  {
    if (this->commandFile.empty() || !boost::filesystem::exists(this->commandFile))
      return false;

    std::time_t mtime = boost::filesystem::last_write_time(this->commandFile);
    std::ifstream in(this->commandFile);
    std::ostringstream buf;
    buf << in.rdbuf();
    std::string commandText = buf.str();

    if (mtime <= this->lastCommandMTime && commandText == this->lastCommandText)
      return false;

    std::string line;
    std::istringstream lines(commandText);
    while (std::getline(lines, line))
    {
      if (line.empty() || line.find("x") != std::string::npos)
        continue;

      for (char &c : line)
      {
        if (c == ',')
          c = ' ';
      }

      std::istringstream ss(line);
      double x = 0.0, y = 0.0, z = 0.0, yaw = 0.0;
      if (!(ss >> x >> y >> z >> yaw))
        continue;

      this->commandTarget = ignition::math::Vector3d(
        std::max(-7.0, std::min(6.5, x)),
        std::max(-4.0, std::min(4.0, y)),
        std::max(1.2, std::min(1.8, z)));
      this->commandYaw = yaw;
      this->lastCommandMTime = mtime;
      this->lastCommandText = commandText;
      gzmsg << "[SimpleDronePlugin] command target: "
            << this->commandTarget.X() << ", "
            << this->commandTarget.Y() << ", "
            << this->commandTarget.Z() << ", yaw="
            << this->commandYaw << std::endl;
      return true;
    }

    this->lastCommandMTime = mtime;
    this->lastCommandText = commandText;
    gzerr << "[SimpleDronePlugin] command file changed but no valid x,y,z,yaw found: "
          << this->commandFile << std::endl;
    return false;
  }

  // Called once the final waypoint has been captured. The frame for the last
  // waypoint is already saved by the capture-on-arrival branch, so this only
  // closes the trajectory file and latches the tour as complete (no further
  // motion or recording).
  void FinishTour(const ignition::math::Pose3d &finalPose)
  {
    if (this->trajFile.is_open())
      this->trajFile.close();

    this->holdPose = finalPose;
    this->model->SetLinearVel(ignition::math::Vector3d::Zero);
    this->tourComplete = true;

    gzmsg << "[SimpleDronePlugin] trajectory complete: visited "
          << this->waypoints.size() << " waypoints, saved "
          << this->frameCounter << " frame sets. Recording stopped."
          << std::endl;

    if (this->quitOnFinish)
    {
      if (!this->doneFile.empty())
      {
        std::ofstream done(this->doneFile, std::ios::out | std::ios::trunc);
        done << "done\n";
        done.flush();
        gzmsg << "[SimpleDronePlugin] wrote done file: "
              << this->doneFile << std::endl;
      }
      gzmsg << "[SimpleDronePlugin] SIMPLE_DRONE_QUIT_ON_FINISH set; shutdown requested."
            << std::endl;
      gazebo::shutdown();
    }
  }

private:
  physics::ModelPtr model;
  physics::WorldPtr world;
  event::ConnectionPtr updateConnection;

  // Cameras (front / down / left / right).
  std::vector<std::string> cameraNames;   // sensor names, must match the SDF
  std::vector<std::string> folderNames;   // output sub-folder per camera
  std::vector<sensors::CameraSensorPtr> cameras;
  std::vector<event::ConnectionPtr> imageConnections;
  bool camerasReady;
  std::string imageDir;
  double capturePeriod;          // legacy, unused (capture is per-waypoint now)
  common::Time lastCaptureTime;  // legacy, unused
  unsigned int frameCounter;
  std::ofstream trajFile;

  std::vector<ignition::math::Vector3d> waypoints;
  unsigned int targetIndex;
  // Settle-then-capture state: while parked on a waypoint we wait for the
  // cameras to re-render from the pinned pose before saving, so each image
  // matches its logged coordinate exactly.
  bool settling;                 // true while parked on a waypoint awaiting capture
  bool settleBaselineSet;        // have we latched the pre-settle render times?
  bool captureFailureWarned;     // avoid spamming camera readiness diagnostics
  bool settleTimeoutWarned;      // avoid spamming settle timeout diagnostics
  double captureYaw;             // heading to hold while settling (travel heading)
  std::vector<common::Time> baseRenderTime;  // per-camera render time at snap moment
  common::Time settleStartTime;
  const double settleTimeout = 10.0;
  double speed;
  common::Time lastTime;

  // One-shot tour state: once the last waypoint is reached the drone hovers
  // at `holdPose` and stops capturing.
  bool tourComplete;
  ignition::math::Pose3d holdPose;

  // Dataset trajectory mode. Trajectories are read from
  // <datasetRoot>/trajectory/*.csv. Captures are saved into
  // <datasetRoot>/images/<trajectory_name>/images_{front,down,left,right}/.
  bool datasetMode;
  bool quitOnFinish;
  std::string doneFile;
  bool returningToStart;
  std::string datasetRoot;
  std::string trajectoryDir;
  std::string datasetTrajectoryFile;
  std::vector<DatasetTrajectory> datasetTrajectories;
  size_t currentDatasetTrajectory;

  // File-based Python control mode. After each captured frame set, the drone
  // holds position until Python writes x,y,z,yaw to commandFile.
  bool commandMode;
  bool waitingForCommand;
  std::string commandFile;
  std::string lastCommandText;
  std::time_t lastCommandMTime;
  ignition::math::Vector3d commandTarget;
  double commandYaw;

  bool rejectGrayImages;
  int grayDelta;
  int grayMin;
  int grayMax;
  double grayMaxRatio;
  double grayTileRatio;
  double grayScanlineRatio;
  double minLumaStd;
  int minRgbRange;
  double viewDownTilt;
  double minValidImageRatio;
  unsigned int grayRejectWarnCounter;

  std::mutex frameMutex;
  std::vector<CachedFrame> latestFrames;
  bool physicalSequenceInProgress;
  size_t physicalViewIndex;
  bool physicalWarned;
  bool physicalViewArmed;
  common::Time physicalBaselineTime;
  unsigned int physicalRejectCount;
  bool physicalFallbackToSweep;
  std::vector<CachedFrame> physicalFrames;
  bool sweepInProgress;
  bool sweepPoseSet;
  size_t sweepViewIndex;
  unsigned int sweepYawAttempt;
  bool sweepTimeoutWarned;
  common::Time sweepStartTime;
  common::Time sweepBaselineFrameTime;
  ignition::math::Pose3d sweepBasePose;
  std::vector<CachedFrame> sweepFrames;
};

GZ_REGISTER_MODEL_PLUGIN(SimpleDronePlugin)
}