Altitude inconsistant

Sparky · 01-25-2008, 8:41 PM

I'm new to using a GPS in a car. I've had the 2100 for a week now and really like the graphics and reality view. I live near the Gulf of Mexico, so often I am driving at sea level. It seems the altitude reading is all over the place from -10 feet to +60 feet and everywhere in between. Am I expecting too much precision from this device? Would not be good for flying an airplane.

Andy · 01-26-2008, 12:52 PM

That is fairly common. Altitude seems to be a weak point with GPS. I see the same thing with all of mine. Near sea level they'll be -20 or up to 100. Both my 76S and 76CSx also have a barometric altimeter and switching back and forth between the gps elevation and the one based off pressure gets a good average most of the time.

If the 2100 has a setting to reset the elevation or calibrate it try that. Mine are more accurate if I go down to the beach and calibrate the elevation.

egadgetguy · 01-28-2008, 5:41 PM

Yes that's normal! Why it's normal is all about the fact that the satellites are above you, and triangulation of position is more accurate. add to that the goedesic base is not always at sea level, but averaged. See, the earth isn't round! It's an elipse, and not a perfect elipse. Most GPSs in the US for instance use WGS84 [1984] datum. The "sea level" setting is not perfect everywhere, so it's not exact.
Hi precision, long term averaging GPS units used in GIS can get much better accuracy, however. On the order of cm position, but still only a few dm [decimeters] altitude. and YES, using barametric altimeters can really help.

01-25-2008, 8:41 PM	#1
Sparky Join Date: Jan 25 2008 Location: Tampa, Florida Posts: 8	Altitude inconsistant I'm new to using a GPS in a car. I've had the 2100 for a week now and really like the graphics and reality view. I live near the Gulf of Mexico, so often I am driving at sea level. It seems the altitude reading is all over the place from -10 feet to +60 feet and everywhere in between. Am I expecting too much precision from this device? Would not be good for flying an airplane.

01-26-2008, 12:52 PM	#2
Andy Survey Says? Join Date: Dec 29 2006 Location: Monterey, CA Posts: 532	Re: Altitude inconsistant That is fairly common. Altitude seems to be a weak point with GPS. I see the same thing with all of mine. Near sea level they'll be -20 or up to 100. Both my 76S and 76CSx also have a barometric altimeter and switching back and forth between the gps elevation and the one based off pressure gets a good average most of the time. If the 2100 has a setting to reset the elevation or calibrate it try that. Mine are more accurate if I go down to the beach and calibrate the elevation.

01-28-2008, 5:41 PM	#3
egadgetguy Join Date: Dec 31 2007 Location: Auburn, AL Posts: 32	Re: Altitude inconsistant Yes that's normal! Why it's normal is all about the fact that the satellites are above you, and triangulation of position is more accurate. add to that the goedesic base is not always at sea level, but averaged. See, the earth isn't round! It's an elipse, and not a perfect elipse. Most GPSs in the US for instance use WGS84 [1984] datum. The "sea level" setting is not perfect everywhere, so it's not exact. Hi precision, long term averaging GPS units used in GIS can get much better accuracy, however. On the order of cm position, but still only a few dm [decimeters] altitude. and YES, using barametric altimeters can really help. __________________ emap> Magellan MAP410> GPSV JensenNVX200 >Garmin Nuvi200> Navigon 2100 MIO C230 >GPSV

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