Constraint Equations in Cadastral Modelling

Cadastral modelling uses the cadastral data including bearings and distances of boundary lines to calculate coordinates of boundary corners and associated marks, and to evaluate the data. This paper shows that at sites where several boundary corners are intended to be on a straight line a Least Squares adjustment of the boundary data may cause the points to move away from one straight line. M e t h o d s o f c o n s t r a i n i n g b o u n d a r y c o r n e r s t o s t a y o n s t r a i g h t l i n e s , when that is desired, in a Least Squares solution of cadastral boundary data are described in this paper. The LS process and equations are given for constraining points to stay on a straight line by using fixed 180° angle observations or by using parameter constraint equations. Also, considered are multiple points on a line, parallel line constraints and constraints to keep boundary points on a circular arc, where appropriate. An example is given to demonstrate the application and effect of the constraints.