Added get_shape_at_point() for (neutral) shape model only

include/eos/fitting/ceres_nonlinear.hpp

@@ -373,6 +373,30 @@ struct VertexColorCost
     const eos::core::Image3u& image; // the observed image
 };
 
+/**
+ * Returns the 3D position of a single point of the 3D shape generated by the parameters given.
+ *
+ * @param[in] shape_model A PCA 3D shape model.
+ * @param[in] vertex_id Vertex id of the 3D model that should be projected.
+ * @param[in] shape_coeffs A set of PCA shape coefficients used to generate the point.
+ * @return The 3D point.
+ */
+template <typename T>
+Eigen::Vector3<T> get_shape_at_point(const eos::morphablemodel::PcaModel& shape_model, int vertex_id,
+                                     Eigen::Map<const Eigen::VectorX<T>> shape_coeffs)
+{
+    // Computing Shape = shape_mean + shape_basis*shape_coeffs:
+    const Eigen::Vector3f shape_mean = shape_model.get_mean_at_point(vertex_id);
+    // Note: We seem to have a dependent name here, so we need 'template', to help the compiler that 'cast<T>'
+    // is a template.
+    const Eigen::Vector3<T> shape_vector = shape_model.get_rescaled_pca_basis_at_point(vertex_id)
+                                               .leftCols(shape_coeffs.size())
+                                               .template cast<T>() *
+                                           shape_coeffs;
+
+    return Eigen::Vector3<T>(shape_mean.cast<T>() + shape_vector);
+};
+
 /**
  * Returns the 3D position of a single point of the 3D shape generated by the parameters given.
  *