TPC Technote

Survey Units

A survey unit is one basic unit of measure, in whatever system you are using. If you use a metric system, a unit is one meter. If you use an imperial system, a unit is one foot, chain, rod or pole. Regardless of the unit you use, the entire survey consists of one unit (every coordinate is feet, meters, chains, etc.).

The formulas used in TPC to compute coordinates, central angles, stations, etc. are "unitless" - they work the same whether the survey units are imperial, metric or some unique user defined value. When TPC computes the elevation of a foresight, it knows the instrument height, target height and control point elevation are so many units.

It’s up to the user to keep the units consistent. If your coordinates are in feet, the values used to compute coordinates should be in feet.

Setting default units

Each time you start a new survey, TPC uses the default units for the new survey. To set the default units, choose Tools | Program Settings | Units (TPC Desktop), Opt | Program Settings | Units (TPC Handheld v1.x), Options | Program Settings | Units (TPC Handheld v2.0) from the Survey View/Screen. This won’t affect the current survey, but will effect any new surveys.

Changing units in a survey

To change the units in an existing survey, load the survey and choose Options, Coordinate Conversion (TPC Handheld), Tools, Coordinate Conversion (TPC Desktop) from the Survey Screen/View. TPC displays the current units and allows you to select the new units. Note the Factor used to convert the survey. If you are converting from imperial to metric or vice versa, you can change the ratio by selecting U.S. Survey Foot or Int’l Survey Ft.

Area

TPC reports area based on the current survey units. If the survey is in meters, area is reported as square meters and hectares. If the survey is in imperial units, the area is reported as square feet and acres.

Quick View

The survey units affect how Quick View reports sizes and scales. If the survey is in meters, TPC reports paper sizes in centimeters and text sizes in millimeters. Scale is a ratio where 1:1000 means that one cm on the drawing is equal to 1000 cm on the ground.

If the survey is in imperial units, TPC reports paper and text sizes in inches and scale as feet to the inch, where 40 means that one inch on the drawing is equal to 40 feet on the ground.