Elevation error?

[wlepse]

OK...not sure if this is a TT1 issue or something to do with Tripmaster or Offroad apps. But the elevation listed is way off. I was driving down a road that is right along the ocean, maybe 10 feet asl and it was indicating -80! i checked both apps and they said the same thing so eiher it is the way they calculate it, the sats giving eroneous data or the TT1 is doing something messed up. Any ideas what I could do to correct this?

 

[ftldny]

GPS elevation accuracy is nowhere near as good as horizontal accuracy. I haven't seen any published specs from TomTom, but here's a quote from a GPS FAQ:

Q: Why does the elevation fluctuate on my GPS receiver?
A: GPS elevation will vary up to 150 meters due to Selective Availability. Now that SA has been turned off, the accuracy of GPS elevation may vary +/- 15-20 meters (50-65 feet) due to random errors caused by atmospheric delay, incorrect satellite positioning or poor geometry in the satellite constellation.

http://www.prairie.mb.ca/magellan_faq.php

 

[adytzu]

Sorry, but my TT1 XL don't have elevation on the settings. How can I see it?

 

[wlepse]

Either Tripmaster or Offroad apps whille give you the elevation. When I was using this at home it seemed fairly stable and accurate though it did seems to lag behind actual point. On my way home as I go over the mountain it would indicate the right elevation but maybe 200 yards past the crest. Right now it is very suspect since it did read as low as -80 feet when I was 10 feet asl according to google earth. So the error is 90 feet and seems a bit excessive compared to the numbers given above. Is there a way to calibrate this?

 

[vroomfondel]

There is a basic misunderstanding here. GPS does not give accurate absolute elevation period. Its calculated assuming the earth is a geometrical spheriod.
The relative elevations in a given area are reasonably consistent.
As has been said elsewhere "do not land your light aircraft relying on GPS!"

 

[adytzu]

Sorry, I'm the newbie in this disscution, but...you can install another application on the TomTom One device?!?!

 

[digital-flex]

Sorry, I'm the newbie in this disscution, but...you can install another application on the TomTom One device?!?!

Yes, there are 3rd party applications that you can install. Check out the 3rd party forum.