# Working with 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. This won't affect the current survey, but will affect any new surveys.

## Changing Units in a Survey

• To change the units in an existing survey, load the survey and choose Tools | Coordinate Conversion from the Traverses Manager. 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.

## Drawing View

The survey units affect how Drawing View reports sizes and scales. If the survey is in meters, TPC reports 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 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.

## Traverse and Closure View

You can select the appropriate units for any traverse in the Traverse View Format dialog.  These units are used to display horizontal and slope distances in the Traverse View and to display closure data in the Closure View.

## User Defined Units

TPC comes with predefined unit factors for common distance units like Chains, Poles, Perches, Rods and Varas. But you can also enter your own User Defined units factor to be used just like the predefined factors.

You enter this in the Units pulldown field in the Traverse View Format, Advanced tab.

## COGO

Many COGO routines can display data and will allow you to enter data in whatever units you want. Look for a Show Options button to show the Units pulldown list. Then select the units you want from the list.

## Editing

You can change the units the program works with for the current survey and also for any new surveys you create.

• Choose Tools | Program Settings | Units.
• Choose the distance, direction and angle units that you want to use.
• You can also edit the text that TPC uses to display distances and areas (i.e. FT vs. ‘).
• When you are finished, choose OK. The changes you make here affect both the current survey and any new surveys you start.

Related Topics