M. Low Distortion Projections

1. Different Design Approach

The maximum distance distortions for SPC and UTM system design are 1/10,000 and 1,2500, respectively. In both cases, the distortion is from ellipsoid to grid - the grid scale k.
Measurements, however, are made at some distance removed from the ellipsoid. Reducing from ground to ellipsoid introduces another distortion. The Combined Factor, EF x k, is the total distortion from ground to grid, Figure M-1.

Figure M-1
Distance Distortions

Depending on location in the zone, orientation, elevation, and geoid height, the total distortion may approach or exceed the design standard. Even though distortions are systematic, their compensation adds another layer of computations and potential confusion.