J. Reduction Example: Survey & Control

1. General

To fit a grid system, most surveying measurements will need modification to account for projection distortion. Depending on the survey purpose and quality, computations may be simple or involved

To reduce measurements, it is necessary to know

distance: elevation, geoid height, grid scale
direction: convergence
angle: false easting (Eo, cylindric) or false northing (No, conic)

A survey must be connected to at least one known control point, from whose datasheet most of this data can be extracted. Others data may require software, like NGS's NCAT.

This chapter will introduce some survey data and control information. Chapter K will show measurement reduction for a conic SPC system, Chapter L for a cylindric UTM system.