Function MakeBehindCameraImage

src/colmap/mvs/texture_mapping_test.cc:96–122

Create a camera where the mesh at Z=0 is behind the camera. Camera at (0.5, 0.5, -5), looking along -Z in world (away from mesh).

// Create a camera where the mesh at Z=0 is behind the camera.
// Camera at (0.5, 0.5, -5), looking along -Z in world (away from mesh).
Image MakeBehindCameraImage(int width, int height) {
  float K[9] = {0};
  K[0] = static_cast<float>(width);
  K[4] = static_cast<float>(height);
  K[2] = static_cast<float>(width) / 2.0f;
  K[5] = static_cast<float>(height) / 2.0f;
  K[8] = 1.0f;

  // R: 180° around X, looks along -Z in world.
  float R[9] = {1, 0, 0, 0, -1, 0, 0, 0, -1};

  // C = (0.5, 0.5, -5), T = -R*C = [-0.5, 0.5, -5]
  float T[3] = {-0.5f, 0.5f, -5.0f};

  Image image("behind.png",
              static_cast<size_t>(width),
              static_cast<size_t>(height),
              K,
              R,
              T);

  Bitmap bitmap(width, height, /*as_rgb=*/true);
  bitmap.Fill(BitmapColor<uint8_t>(0));
  image.SetBitmap(std::move(bitmap));

  return image;
}

// Create a camera that views the mesh at a very grazing angle.
// Camera nearly in-plane with XY mesh, at (0.5, 0.5, 0.01), looking along -Z.