Control Surveying and Geodetic Surveying
Core concepts
Control provides the framework for all surveys. Candidates must understand horizontal and vertical control, the difference between geodetic and assumed coordinates, state plane coordinate systems, map projections, and the effect of scale factor and elevation factor on ground distances. Alabama spans two state plane zones (East and West), each with its own projection parameters.
Traps
A classic trap is applying the combined factor in the wrong direction. Ground distance times combined factor gives grid distance; grid distance divided by combined factor gives ground distance. Another trap: confusing ellipsoid height with orthometric height (the geoid separation). Also watch for questions on traverse closure-angular misclosure is distributed before linear misclosure, and precision is expressed as a ratio.
Worked example
A ground distance of 1,000.000 ft with a combined factor of 0.99995 gives a grid distance of 999.950 ft. To recover ground from grid, divide: 999.950 / 0.99995 = 1,000.000 ft.
Rule of thumb
Grid = Ground × Combined Factor; Ground = Grid ÷ Combined Factor.