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Using Autonomous GPS with Earthwork 3D/SiteModel 3D
Autonomous GPS positioning has been added to the Earthwork 3D and Sitemodel Grade window. Autonomous GPS connected to a Tablet PC or Laptop allows the user to walk on the site while showing the 3D view. The notes below explain how to configure and use this feature.
GPS CompatibilityBoth Garmin and SIRF chipsets have been run with success with either a Bluetooth or a serial connection. Garmin produces consumer GPS devices under their brand name. SIRF is a chipset manufacturer selling to a variety of companies for packaging to consumers. Some GPS brands and models that we have used successfully are:
- TeleType GPS CF v3.0 Receiver Code:1653 (CF Card included with PlanPilot)
- Garmin GPS 10 (Bluetooth)
- Holux GPS Slim 236 (Bluetooth)
There are several dozen autonomous GPS's available with the majority being SIRF based. Be aware that the SIRF based equipment is configured by the manufacturer and some are optimized for vehicle tracking and less suitable for our use because of signal damping.
Configuring
There are two one-time steps to configuring the GPS for use with Earthwork. The first is to get a Com port assigned from your computer. This is going to vary between computers and the GPS so look at the documentation that came with GPS. The second step is to configure Earthwork 3D/SiteModel. The steps are:
- Start Earthwork 3D/SiteModel.
- Open a job file.
- Change to the 3D View window.
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- The configuration window displays. Select the Com Port assigned to the GPS. The remainder of the default settings are usually correct for most autonomous GPS.
- Press the Test button to check the connection and then press OK.
As long as the GPS remains on the same Com port you should not need to do this again.
Starting
With the GPS configured, select GPS-Enable from the Instrument menu.
The program tries to get a valid position from the GPS and displays the window below until a position is received.
Time to Fix
Autonomous GPS receivers do not instantly provide position (latitude, longitude) when switched on but automatically start the process. To minimize delays in initializing, turning the GPS on as soon as possible minimizes the initialization time. This can be done by powering up the computer the GPS is inserted into (CF Cards) or using the on/off switch on the GPS (bluetooth). The time to get a fix position is going to vary with the GPS, the current satellite coverage and the sky exposure. Typically the more it's used, the faster it will get a good position. Earthwork/SiteModel will stay at the Initializing screen until a valid position is received. At that point the GPS window displays in the lower right.
Setting the Location
The first valid position received places you at the center of the job. To place yourself at the correct job location, do the following:
- Walk to a known location on the job.
- Press the Bullseye button and select that location on the screen. The GPS shoots and places you at that location.
Align to the Job
As you walk the site if movement direction on job doesn't match the screen you'll need to align. Earthwork/SiteModel assumes that the job coordinates are in a true north orientation. If they are not you need to use the Alignment button to correct the rotation. The steps are listed below.
- Walk to another known location on the job.
- Press the Alignment button and select that location on the screen. The GPS shoots and corrects the rotation. Now your movement on screen should match the job.
Using GPS with Earthwork/SiteModel
Once enabled and Bullseyed to the job the GPS readings show your position on the 3D model as you move over the site. The Cut or Fill at your current location displays by comparing the Ref and Diff surfaces at your GPS location but does not use the GPS elevation in its calculation. Autonomous GPS does not have the accuracy of RTK GPS but is many times cheaper. As you walk you may find that you're a little off of know points. You can correct for this error by using the Bullseye button while standing over and selecting the known location. Typically accuracy increases the longer the GPS is on so you'll probably need to bullseye more than once.
