2.1.4.1 Coordinates, coordinate differences and distances (metric observations)

The equations for these observations are trivial and need no explanation here. These observations are used for orientation and strengthening of networks as well as specification of a datum. The coordinate differences may also be used for formulation of local levelling nets, conditions for perpendicular lines, straight lines and planes parallel to the axes of the coordinate system. They can be applied as well for lake levelling. Thus for example coordinate axes can be fixed parallel to the axes of the object in question.