Does anyone know how to carry out the method of planar interpolation in Openroads, I got confused I saw one version with dot and cross product and then another where they are using linear interpolation from a point inside the triangle to the faces of the triangle, inside the the digital terrain model. My guess is that they are using linear interpolation, but what is their procedure and what is terrain extractor doing when it looks at the hydraulic model node ( point) elements and interpolates their elevation by first finding the face that the point is on.