Surveying on a Plane ERS
• The points A and B are on the ERM surface
• The reference distance AB on the ERM is also the Euclidean distance from A to B in the coordinate frame
• The normals at A and B are co-planar
• The azimuth ? (or any angle) is readily defined
• Note that z is not involved, and chaining would be easy
• By definition there is no terrain surface