Function BuildPerspectiveCameraModel

src/colmap/ui/model_viewer_widget.cc:224–324

Builds a viewing frustum (image plane as two triangles, plus the frame and connecting lines to the projection center) for a perspective camera.

// Builds a viewing frustum (image plane as two triangles, plus the frame and
// connecting lines to the projection center) for a perspective camera.
void BuildPerspectiveCameraModel(
    const Eigen::Matrix<float, 3, 4>& world_from_cam_mat,
    const Camera& camera,
    const float image_width,
    const float image_height,
    const float image_extent,
    const RGBAColor& plane_color,
    const RGBAColor& frame_color,
    const bool show_camera_orientation,
    std::vector<TrianglePainter::Data>* triangle_data,
    std::vector<LinePainter::Data>* line_data) {
  const float camera_extent = std::max(camera.width, camera.height);
  const float camera_extent_normalized =
      static_cast<float>(camera.CamFromImgThreshold(camera_extent));
  const float focal_length = 2.0f * image_extent / camera_extent_normalized;

  // Projection center, top-left, top-right, bottom-right, bottom-left corners.
  const Eigen::Vector3f pc = world_from_cam_mat.rightCols<1>();
  const Eigen::Vector3f tl =
      world_from_cam_mat *
      Eigen::Vector4f(-image_width, -image_height, focal_length, 1);
  const Eigen::Vector3f tr =
      world_from_cam_mat *
      Eigen::Vector4f(image_width, -image_height, focal_length, 1);
  const Eigen::Vector3f br =
      world_from_cam_mat *
      Eigen::Vector4f(image_width, image_height, focal_length, 1);
  const Eigen::Vector3f bl =
      world_from_cam_mat *
      Eigen::Vector4f(-image_width, image_height, focal_length, 1);

  // Image plane as two triangles.
  if (triangle_data != nullptr) {
    const auto add_triangle = [&](const Eigen::Vector3f& p1,
                                  const Eigen::Vector3f& p2,
                                  const Eigen::Vector3f& p3,
                                  const RGBAColor& color) {
      triangle_data->emplace_back(
          PointPainter::Data(
              p1(0), p1(1), p1(2), color(0), color(1), color(2), color(3)),
          PointPainter::Data(
              p2(0), p2(1), p2(2), color(0), color(1), color(2), color(3)),
          PointPainter::Data(
              p3(0), p3(1), p3(2), color(0), color(1), color(2), color(3)));
    };
    add_triangle(tl, tr, bl, plane_color);
    add_triangle(bl, tr, br, plane_color);

    if (show_camera_orientation) {
      const Eigen::Matrix3f world_from_cam_rot =
          world_from_cam_mat.block<3, 3>(0, 0);

      const Eigen::Vector3f right_dir = world_from_cam_rot.col(0);
      const Eigen::Vector3f up_dir = -world_from_cam_rot.col(1);
      const Eigen::Vector3f forward_dir = world_from_cam_rot.col(2);

      // Size + offset
      const float size = 0.5f * image_extent;