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Elevation on my GPS


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I have a GARMIN map 60CSx- I was recently at the ocean-definitely sea level and my GPS read 70 meters above sea level- Does anyone know if this is normal or is there a process I have to go through to calibrate my GPS- I have calibrated the compass but this has not affected the elevation I have gone to a few sites to find the elevation where I am and it also is different by about 50 meters-

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I have calibrated the compass but this has not affected the elevation I have gone to a few sites to find the elevation where I am and it also is different by about 50 meters-

calibrating the compass won't effect elevation, calibrate the barometric altimeter.
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I have a GARMIN map 60CSx- I was recently at the ocean-definitely sea level and my GPS read 70 meters above sea level- Does anyone know if this is normal or is there a process I have to go through to calibrate my GPS- I have calibrated the compass but this has not affected the elevation I have gone to a few sites to find the elevation where I am and it also is different by about 50 meters-

 

The 60Csx has a barometric altimeter. There is a way to calibrate it, but I'm not familiar with how to do that. Check your manual.

 

Also, with the barometric altimeter turned off, altitude is the least precise measurement a GPS makes. It can be off by up to 100 feet either way. Usually it isn't, but you have to watch for it. I was just in Hawaii last week and with the ocean lapping at my feet, my Oregon said that I was at -52 feet (and +30 feet in roughly the same spot a day later).

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What was the GPS Elevation when you were at sea level, and where you are now?

 

( Sat Page>Menu>GPS Elevation>Entr )

 

That's one reason I like the 60Cx better than the 60CSx; I don't have to dink with Altimeter Calibration, just go with the GPS Elevation, which is good enough for my uses.

 

I suppose that if I was going to be at the beach for a while, I could set the Altimeter to zero. then see how much change took place in the Alti/Baro, while I was there.

 

Just cut on my 60CSx, ( I'm inside, GPS off ) which has been off for several days, and the Barometer is dead on at 29.50, but the Elevation is a bunch off, showing 6965, correct is 6580. If I connect to the ex ant on the roof, it usually takes from 30 min to an hour for the altimeter altitude to self correct to the GPS Elev.

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I have a GARMIN map 60CSx- I was recently at the ocean-definitely sea level and my GPS read 70 meters above sea level- Does anyone know if this is normal or is there a process I have to go through to calibrate my GPS- I have calibrated the compass but this has not affected the elevation I have gone to a few sites to find the elevation where I am and it also is different by about 50 meters-

The 60CSx has a barometric altimeter and can also output GPS based altimeter readings. The barometric altimeter, as you have seen can get to be a bit inaccurate. The inaccuracy is a function of local atmospheric conditions, i.e. weather.

 

To calibrate the barometric altimeter...setup, calibration, altimeter, Yes/No...If you know the correct elevation you can use that, if you want it to use GPS elevation you can use that. If you have the altimeter page as one of the ones being display you can use that as a starting point. From the Altimeter page, menu, calibrate altimeter, Yes/No...same as before.

 

In my experience I haven't seen an particular usefulness of the barometric altimeter. The GPS based altitude has always been fine for my uses. One oddity that might be of interest is comparing the GPS and barometric values while flying in an airplane. When cruising at altitudes of 28kft to 40kft my barometric altimeter has read 6kft to 8kft.

 

Garmin supposedly has some algorithm to automatically calibrate the barometric altimeter with GPS based data without user intervention. I haven't ever seen documentation on how they do that.

 

To get output of the GPS based altitude...from the satellite page, menu, GPS elevation.

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When cruising at altitudes of 28kft to 40kft my barometric altimeter has read 6kft to 8kft.
That is because the cabin is pressurized.

The vertical 'error zone' on a GPSr is usually quoted at 2-1/2 to 3 times that of the horizontal - although I did see one professional authority saying it can be as much as 4 times.

Edited by snowfleurys
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I have a GARMIN map 60CSx- I was recently at the ocean-definitely sea level and my GPS read 70 meters above sea level- Does anyone know if this is normal or is there a process I have to go through to calibrate my GPS- I have calibrated the compass but this has not affected the elevation I have gone to a few sites to find the elevation where I am and it also is different by about 50 meters-

 

The 60Csx has a barometric altimeter. There is a way to calibrate it, but I'm not familiar with how to do that. Check your manual.

 

Also, with the barometric altimeter turned off, altitude is the least precise measurement a GPS makes. It can be off by up to 100 feet either way. Usually it isn't, but you have to watch for it. I was just in Hawaii last week and with the ocean lapping at my feet, my Oregon said that I was at -52 feet (and +30 feet in roughly the same spot a day later).

I was also in hawaii where I first thought the elevation was off- maybe sea level is different in Hawaii due to the earth being eliptical?

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Sea level isn't absolute. The term is actually MSL, Mean Sea Level, and it is a measurement over time that averages out affects from wind and waves and tides. On top of that, it can vary something like plus/minus two meters globally.

Good point, when the OP was standing at sea level, was the tide in or out, and where was the moon?

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Sea level isn't absolute. The term is actually MSL, Mean Sea Level, and it is a measurement over time that averages out affects from wind and waves and tides. On top of that, it can vary something like plus/minus two meters globally.

 

If you are referring to the difference between MSL and the WGS-84 ellipsoid, it is more like 50-100 meters!

 

Your handheld GPS unit has in it a rough geoid that corrects for the MSL difference from the WGS-84 ellipsoid everywhere, but I doubt that the horizontal resolution is all that great.

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