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This option allows you to select either the US Survey Foot or the International Foot for all COMPASS operations. Once you have set this option, all COMPASS programs will use the units you have selected whenever it converts between feet and meters. When you change options, the change will take effect immediately for the Project Manager; however, any of the sub programs such as the Viewer or Editor must be re-run for the change to take effect.
Foot Units. There are two different standards for the Foot. One is called the International Foot and the other is called the US Survey Foot. The International Foot is defined as 0.3048 of a meter and the US Survey Foot is defined as 0.304800609601, which makes it 0.000024 inch longer. This may not sound like much, but if you are working with UTM coordinates in the northern United States, the conversion difference can be as much 35 feet.
The US Survey Foot is and has been widely used for mapping, benchmarks and surveying. It was used for the 1933 State Plane Coordinate System and is still mandated for certain federal projects. For this reason, COMPASS offers the option of using either unit.
For most things, the choice of units will make little difference. It has no effect on any measurements or coordinates that were originally entered in meters and displayed as meters. However, any measurements that were originally in one unit and displayed in another can be effected. Also, for small numbers less than about 200 kilometers or 100 miles, the choice of units makes little difference. However, for larger numbers like UTM coordinates, the units can make a relatively large difference.
If you are working with feet units that will be converted or displayed as UTM in meters or UTM units that will be converted or displayed as feet, it is important to know if your reference points and maps using the US Survey Foot or the International Foot. At this point, most maps that displays feet will be using the US Survey Foot.