Choosing a Coordinate Reference System

A survey can have one Coordinate Reference System (CRS) that relates it's geodetic and rectangular coordinates.

Selecting a CRS for a New Survey

• From the Survey Information dialog, choose Coordinate Reference System.
• Select a Name from the pull down list.
  
• Selected a CRS from the list then select a corresponding Zone and Horizontal Datum.
  
• Enter a Combined Factor. This factor relates your measured data to grid coordinates and can be applied to individual traverses as needed.
  
• Choose Ellipse to edit or check the ellipse data used in the computations.
  
• If your survey is in Feet, specify whether you want to convert to meters using the International Foot (0.3048 M/FT) or the US Survey Foot (0.3048006096 M/FT).
  
• Choose OK.

The CRS selection you just made is primarily used to convert Latitude and Longitude to rectangular coordinates. This information is stored with the survey in the TRV file.

Changing the CRS of an Existing Survey

To change the CRS of an existing survey without doing a transformation, choose Tools | Survey Information, Coordinate Reference System. Select the options you want and choose OK.

This action simply updates the CRS information stored with the survey. It does not transform any coordinates. If you want to transform the survey from one grid to another, you need to choose Tools | Transform Coordinates from the desktop.

Converting a Survey From One CRS to Another

In order to compare a survey based on one CRS with a survey based on another CRS, you must first convert one survey to the same CRS as another. You might also import data based on one CRS and want to convert it to the survey CRS.

• Make a backup copy of the survey. You might save it under a different filename.
  
• From the desktop menu, choose Tools | Transform Coordinates. TPC displays the current survey CRS settings in the From box.
  
• Choose the CRS, Zone, Combined Factor and Ellipse you want to convert to.
  
• From the Transform What list, choose All.
  
• Choose OK.

Converting Imported Traverses to the CRS

At times, you might also import data based on one grid and want to convert it to the survey grid. TPC lets you specify the grid settings for those traverses and convert them to the same grid as the survey.

• Make a backup copy of the survey. You might save it under a different filename.
  
• In the Traverses Manager, select the imported traverses you want to convert to the CRS.
  
• From the desktop menu, choose Tools | Transform Coordinates. TPC displays the current CRS in the From box.
  
• Update the CRS in the To box so they match the settings in the From box.
  
• Set the CRS in the From box to match the settings of the imported traverses. TPC has no way of knowing what grid these traverses were based on - you need to supply this information.
  
• From the Transform What box, choose Selected.
  
• Choose OK.

Editing Zone Constants

The CRS parameters and zones are stored in the TpcZone.dat file. Each line contains values for one zone. This file is self documenting, with definitions at the top of the file. To edit the zone values, open this file in any text editor and make the changes.

Related Topics

Coordinate Transformations

Editions

Premium, Professional