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(Sorry if GIS is not the right place to post this question to).

Recently me and my school friends had a GPS software application project to pursue at the university.

A device very similar to this one was used by the application.

One day it refused to show us our current location - it was continuously showing a point in the Atlantic Ocean instead of land [we were outside of any buildings].

I did a double check by opening a default map application on an HTC Desire with Android 2.1 - it showed no current location as well.

Questions:

  1. Does GPS signal quality depend on the chip manufacturer?
  2. Does GPS signal quality depend on weather?
  3. Is it possible to have a commercial hardware-software system which never loses the GPS signal and always shows the correct current position of a user?
whuber
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user10528
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    The point in the Atlantic Ocean was probably the origin point for Latitude and Longitude. This is located just South of Ghana. – jvangeld Jun 16 '11 at 19:06

4 Answers4

3
  1. Yes
  2. Yes
  3. No

Different chip/chipsets do vary in quality and number of channels which affects how fast and well it locks onto satellites. Antenna design is probably going to have a big effect. An iPhone isn't going to get as good reception in your pocket as a Trimble with a Zephyr antenna strapped to your back.

Even with the Zephyr, conditions in the ionosphere and troposhere (weather) will affect the GPS signals. Also, the multipath errors (reflections off canyon walls, buildings, etc.) will introduce further error. You can compensate/correct for these effects somewhat by using other sources of WAAS, differential GPS and CORS.

There is always a chance to lose a GPS signal due to trees, buildings, tunnels and whatnot causing interference. And the concept of a "correct" position is open to interpretation. GPS accuracy with WAAS or differential GPS is still only accurate to ~3 meters.

Sean
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2

You don't live anywhere near where LightSquared was doing the recent LTE testing, do you? Though unlikely, it would be interesting if you were affected by that.

See this question for background: Lightsquared GPS controversy: Where is the analysis?

Community
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Mark Ireland
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Check out this Wiki page on GPS error - it should tell you everything you need to know. There are sections on natural and artificial sources of interference that are most applicable to your question.

Radar
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    It's best to give an answer along with pointers to other resources even if you just summarize what the other resource says. – Sean Jun 16 '11 at 19:48
1

There is more to this answer than posted above.

1)the ability get a position FIX is based on the resolution of the receiver. Meaning, the high resolution you want to capture, the better the signal needs to be. A high end 30k RTK wont give you a fix in an area that a cell phone probably will. Its not that the reception is or isn't there; or that a high end reciever will "get" a better signal, but that one needs more information in order to gain a better more accurate fix. Now having some huge antenna is a bit different and if you can somehow increase your visible satellites then that is different too.

Signal robustness is determined by the number of satellites visible to your receiver. Atmospheric conditions (including but not mainly what you would consider weather) play a small role for the end user, as they are mostly corrected already for you.

Your iphone or smartphone is going to give you your most reliable position location because it is open to the crappiest signals - hence its large errors.

Thad
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