What to do when GPS signals are not available?

GPS mapping depends on your receiver’s ability to receive the signals sent out by the orbiting satellites and to compute its position. When working under heavy canopy or inside buildings, the GPS signals are considerably weakened or blocked altogether. What’s a person to do under those conditions?

As mentioned in our blogpost dated 7/17/11, you  could join a Wi-Fi network and use the Location Services on your iOS device to obtain position information, which is not as accurate as that obtained from a GPS device.

If you are running the iCMTGIS app, you could switch to the Traverse mode and record angles and distances that reference back to the last known position. So, suppose you would like to record the location of a number of artifacts that you’ve found inside a large cavern. What you could do is to first log a good GPS point near the entrance to the cave then use that point as the first reference point for the Traverse measurements inside the cave.

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