+ * calculate the projection, p, of u along the direction of d.
+ * @param p (out) the projection
+ * @param u (in) the vector to be projected
+ * @param d (in) the direction onto which we project
+ */
+void sgProjection(sgVec3 p, const sgVec3 u, const sgVec3 d);
+void sgProjection(sgdVec3 p, const sgdVec3 u, const sgdVec3 d);
+
+
+/**
+ * Map i.e. project a vector onto a plane.