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GPS Mapping Software - Modify GPS track data using the 'Shift Track' tool - Tutorial

Introduction

There are scenarios in which you have to modify an existing or recorded (GPS) track. For instance, when a track is created using with a GPS with an incorrect map datum (other then WGS84) set, or when the position error is known. Instead of editing all the fixes by hand, you can use the built in 'Shift Track' tool, offered by the GPS Mapping Studio software.

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Starting the 'Shift Track' tool

The tool can be used to modify a complete GPS track, a single GPS fix or a selection of GPS fixes. To start the tool, right click the GPS track you want to modify in the "Project Explorer" and select the "Shift Track..." option. When started from the "Project Explorer" the complete GPS track is selected for editing.

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To edit only a single fix, or a selection of multiple fixes, right click the GPS track you want to modify in the "Project Explorer" and select the "Edit..." option. The track editor now appears. Select the fixes you want to edit, and right click the selection. Now select the "Shift Track Points..." option.

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Using the 'Shift Track' tool

The 'Shift Track' tool should now appear. It should look like this:

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Shift track by distance and course

Using this option, you can reproject the selected fixes using the entered distance and course. The new location is calculated by using Vicenty's formula. Enter a distance in meters, and angle in degrees.

Shift track by X and Y distance offset

This option allows you to reproject the selected fixes using a fixed x and y offset (delta-x and delta-y). This distance should always be entered in meters.

Shift track by Northing and Easting offset

This option allows you to reproject the selected fixes using a northing and easting offset. In this case, the distance is just entered in map projection units.

Shift track by Latitude and Longitude offset

This is almost the same as the Northing and Easting offset, but instead of projected units, the offset is entered in degrees.

Apply elevation correction

This allows you to correct elevation measurements recorded in the GPS track. When the altimeter was not corrected, or a the reference altitude used was incorrect, you can use this option to correct the measurements.

Invert Elevation

This option reverses the sign off all elevation measurements. Positive values become negative, and the other way around.

Adjust Track Start Time

When a recorded track does not have time and date information, you can add it using this option. The first point will have the time set in the dialog, and the time of the next fixes is increased at one second per fix.

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Running the 'Shift Track' tool

To apply the shift, just click the "OK" button. It is always recommended to make a backup of the track before proceeding. You can also undo the shift by running the tool again, but with reversed values.

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