message: Made the return type of get_texture_coordinates const ref
  In PcaModel, get_triangle_list returned by value before, we changed that recently, because if called in an inner loop, it was quite time consuming. So I think it's best to also return by const-ref here.
diff: @@ -397,7 +397,7 @@ public:
  *
  * @return The texture coordinates for the model vertices.
  */
  - std::vector<std::array<double, 2>> get_texture_coordinates() const
  + const std::vector<std::array<double, 2>>& get_texture_coordinates() const
  {
  return texture_coordinates;
  };
  