Chainage equations give the user the ability to change the chainage at any key point along a primary alignment. The user can place any number of chainage equations within an alignment.
Chainage equations can be used to either increase or decrease the chainage at a nominated point. They are displayed as:
Back Chainage = Forward Chainage.
E.g. 1000.000 = 1500.000 increases the chainage from this point on by 500.000.
Typically the chainage equation is used to control changes to the design of an alignment, so that the change does not affect the chainages along the complete length of the alignment, and can be restricted to the region of change only.
The value of a chainage equation remains constant regardless of whether Configure units are set to Grid or Ground distances.
Note that any editing of an alignment or the objects that make up the alignment, that results in the deletion of a chainage equation point, or the breaking of an alignment into two alignments, results in a new chainage equation.
Deletion of a point with a chainage equation results in a new chainage equation being created at the next key point.
Breaking an alignment into two results in a new chainage equation at the start of the new alignment.
Such system created chainage equations are always computed using grid distance. Always check that the resulting chainage equations are what you desire particularly if you want chainage equations to reflect a previous ground chainage.