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DIY 1cm accuracy RTK-GPS

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by , 11-18-2009 at 08:43 AM (5525 Views)

This project claiming to provide 1cm GPS accuracy is getting a lot of heckling over on the Make Blog. A geophysical survey engineer claims this has little practical purpose without lots of time, pro survey skills and equipment. What does the mp3car community think about this?

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Updated 11-18-2009 at 10:16 AM by Jensen2000

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I added the make link. Glad this sparked some conversation.
The company I work for has the most accurate GPS technology in the world, we can lay a CD case on a table and tell the different between one corner and the other. So this guy claiming accuracy of 1 centimeter is pure garble.
Several points:

1) Using RTK for a more accurate GPS solution requires real-time data from a very accurately surveyed base station (source of the reference data). In order to use this type of system for vehicle navigation, many base stations would be required, as well as the ability to seamlessly hand off between stations.

2) Dual frequency receivers are generally more accurate than single frequency receivers, even using RTK, due to the ability to largely eliminate atmospheric and ionospheric effects. Dual frequency receivers are also much more expensive than their more simple counterparts.

3) Accuracy in a differential GPS setup (which includes RTK) is a function of the distance from the remote to the base station, i.e., the further the remote is from the base, the less accurate the solution. Differential systems state these errors in terms of a base error in addition to a certain error in parts-per-million related to distance.

4) Unlike errors in inertial systems due to drift, GPS errors are step functions, i.e., large instantaneous change, due to the rising or setting of satellites used in the solution set. This can be reduced by filtering the outputs, but still remain an issue even in professional setups.

5) Accuracy in a differential setup is still governed by the geometry of the constellation currently in view. Sources of error are reduced, sometimes almost to zero, but a poor constellation geometry can still lead to a larger positional error.