Pressure Altimeter setting

[abadrs]

My GPS the explorist 600 has the pressure altimeter. Trouble is I'm not sure what to set it to ? I know the altitude at my house but is that what you set it to ? I don't understand how that could be right unless barometric pressure was at sea level .

[QuigleyJones]

Yes you can chose your house elevation

the altimeter calculates quick changes in pressure into changes in elevation (giving you a more accurate elevation). so it dosnt matter what elevation is used as a base.

 

Unless I plan on hiking a mountain I dont bother with the altimeter

[+geowizerd]

What I don't understand is how it knows it is an elevation change, and not a front moving in...

[dogwalkers2]

What I don't understand is how it knows it is an elevation change, and not a front moving in...

This is why it needs to be calibrated regularly (or set to auto calibration - in the case of a Garmin; I don't know if Magellans have the autocalibration feature).

 

As was mentioned in another thread, the barometric altimeter enjoys the benefit of being more stable in the short term (as opposed to GPS calculated altitude, which bounces around in the short term - if you looked at a plot of he GPS altitude, it would be a jagged line as opposed to a smooth line plot of the barometric altitude), while the GPS calculated altitude is better in the long term (as opposed to the barometric altitude which will change as pressure systems move through). Automatic calibration tries to get the best of both worlds by updating the barometric altitude every once in a while to the GPS altitude. Or, if you had accurate altitude information (i.e. from a topo map) you could calibrate it manually every hour or so and enjoy the short term accuracy.

[tlhutch]

The way I do it is by this technique.

 

Locate an ACCURATE Benchmark near your residence or if you live near an airport, use that elevation. Lay the unit on top of the benchmark or go to the measured elevation point at the airport and manually set the elevation. Go directly to your residence and record the elevation at the point where you normally boot the GPSr. Now, each and every time you boot your GPSr to go out, you can calibrate the altimeter.

 

Another technique is to record the ACCURATE Benchmarks in your area and if one is conveniently located in your direction of travel stop by and calibrate the altimeter.

 

If you're not interested in the above amount of precision, just use a Topo Map and note the elevation on a contour, stand on it and set it there.

 

Another way is if you live near an airport or weather station is to call them and get the barometric pressure setting for the area, set that.

 

They are actually better than an aircraft altimeter as the GPS altitude input helps to keep it stabilized better. If a front is passing through your area and you want/need a great deal of accuracy, you have to keep setting either the elevation or the barometric pressure manually until the front passage/pressure stabilizes.

[tlhutch]

My GPS the explorist 600 has the pressure altimeter. Trouble is I'm not sure what to set it to ? I know the altitude at my house but is that what you set it to ? I don't understand how that could be right unless barometric pressure was at sea level .

 

I don't understand the problem. If you set the elevation manually, the barometric pressure will be correct for your elevation or it should be close. The FAA tolerance for aircraft altimeters between airport elevation and barometric pressure setting is 75'.

 

For example in aircraft, the normal practice is to receive the barometric pressure setting from a control tower, set that in the altimeter. The altimeter elevation then must be within 75' of the published airport field elevation to be legally operational.

 

When you manually set the elevation in your GPSr, you're just doing the reverse of the above. If you're that concerned with accuracy you could go to an airport/weather station and check the tolerance of your GPSr.

[+Renegade Knight]

My GPS the explorist 600 has the pressure altimeter. Trouble is I'm not sure what to set it to ? I know the altitude at my house but is that what you set it to ? I don't understand how that could be right unless barometric pressure was at sea level .

 

If you know your elevation, that's what you calibrate it to when you calibrate. Barometric pressure is what it is at the time you set it. It's a fairly accurate way to gage elevation as long as it was calibrated when you used it.

 

Sea Level would have one calibratoin. House level another. Both would be accurate.