setting Altitude on my GPS

[jkoffsuit]

Where can I find an altitude marker to set the altitude on my GPS. I live in Toronto, Ontario, but will be traveling through the airports in Buffalo, Washington, and Seattle in about six weeks.

 

Thanks in Advance.

[+apollosmith]

I'm curious as to why you feel the need to calibrate - it will do little good unless you need/want accurate elevation recordings while in the immediate vicinity and time of the calibration. Calibrating in Buffalo and then flying a pressurized plane to Toronto will not do you any good - you'd be better off just using the GPS-reported elevation.

 

One option is to go to http://www.geocaching.com/mark/ and enter the zip code and try to find a benchmark you could use (U.S. only). Be sure to look for one that has recently been found in good shape (has a smiley face icon) and that has an adjusted (e.g., very accurate) elevation (check the description for "Altitude is ADJUSTED").

 

You can also view them on a Google Map at http://benchmarks.scaredycatfilms.com/

 

I highly doubt you'll be able to find one INSIDE an airport, however. The only benchmarks I've seen at airports are in places that will get you a cavity search and probably a few days of interrogation (at least) if you try to get to them. You wouldn't want to calibrate it inside anyway because the barometric pressure will be off.

 

And even if you do use a benchmark, the accuracy of the elevation reported by the GPSr is not terribly precise even after calibration (+/- 10 feet at very best). (Benchmark elevations, however, are VERY accurate - usually within an inch.) The GPS-derived elevation is fairly accurate (+/- 100 feet at best). You'd probably be just as well off using a good topographic map or even Google Earth to enter the elevation for calibration - you'll probably be well within the error of the GPSr.

 

Another option is to ask the pilot when you get on or off the plane for the current pressure reading (make sure to ask if it is current) and then enter it in the GPSr while still in the jetway. You can also get the current pressure readings for airports or weather reporting stations online. If you're at about the same elevation and within 25 miles or so, use this. Again, this will put you well within the accuracy of the GPSr.

[+Curioddity]

Being as you will be flying, you can get your destination elevations here:

 

http://www.airnav.com/airports/

 

You don't say what kind of GPS you use but the fact that you want to "set" it probably means it has a barometric altimeter in it. Unfortunately, those only remain accurate after you set them until the "atmospheric" barometric pressure changes. The difference between being in a low pressure area (read: storm) and a high pressure area (read: clear skies) can change your altimeter reading by several hundred feet.

 

But airnav.com should give you the information you need to set your altimeter at any airport, and the information is about as accurate as it gets.

 

Pete

[+The Blorenges]

Check out local weather and use the current pressure setting (millibars) and set that into the GPS altimeter setting.

 

Someone asked why would you want to do this...... well, if you set it correctly and then climb a mountain you can verify that the map has the correct altitude shown for the mountain peak

 

The other reason of course for me is being technical I set the altimeter on mine simply because I can

 

Chris (MrB)

[namiboy]

Check out local weather and use the current pressure setting (millibars) and set that into the GPS altimeter setting.

 

Someone asked why would you want to do this...... well, if you set it correctly and then climb a mountain you can verify that the map has the correct altitude shown for the mountain peak

 

The other reason of course for me is being technical I set the altimeter on mine simply because I can

 

Chris (MrB)

 

i was thinking the same thing, if you have an altimeter you might as well set it.

[+Team Cotati]

I'm curious as to why you feel the need to calibrate - it will do little good unless you need/want accurate elevation recordings while in the immediate vicinity and time of the calibration. Calibrating in Buffalo and then flying a pressurized plane to Toronto will not do you any good - you'd be better off just using the GPS-reported elevation.

 

One option is to go to http://www.geocaching.com/mark/ and enter the zip code and try to find a benchmark you could use (U.S. only). Be sure to look for one that has recently been found in good shape (has a smiley face icon) and that has an adjusted (e.g., very accurate) elevation (check the description for "Altitude is ADJUSTED").

 

You can also view them on a Google Map at http://benchmarks.scaredycatfilms.com/

 

I highly doubt you'll be able to find one INSIDE an airport, however. The only benchmarks I've seen at airports are in places that will get you a cavity search and probably a few days of interrogation (at least) if you try to get to them. You wouldn't want to calibrate it inside anyway because the barometric pressure will be off.

 

And even if you do use a benchmark, the accuracy of the elevation reported by the GPSr is not terribly precise even after calibration (+/- 10 feet at very best). (Benchmark elevations, however, are VERY accurate - usually within an inch.) The GPS-derived elevation is fairly accurate (+/- 100 feet at best). You'd probably be just as well off using a good topographic map or even Google Earth to enter the elevation for calibration - you'll probably be well within the error of the GPSr.

 

Another option is to ask the pilot when you get on or off the plane for the current pressure reading (make sure to ask if it is current) and then enter it in the GPSr while still in the jetway. You can also get the current pressure readings for airports or weather reporting stations online. If you're at about the same elevation and within 25 miles or so, use this. Again, this will put you well within the accuracy of the GPSr.

 

Have the manufacturers totally eliminated satellite based altitude capability? I seem to see more and more of these type posts where it seems as though they have. Why? I can't even hazard a guess.

 

I'd imagine that having accurate local altitude information would be reason enough to calibrate the unit. That certainly would reason enough for me.

Edited January 3, 2010 by Team Cotati

[+Curioddity]

Check out local weather and use the current pressure setting (millibars) and set that into the GPS altimeter setting.

Pilots are intimately familiar with this routine. Good old fashion avionics altimeters only have one thing to set: The barometric pressure. The knob is usually identifyable because it will be the one with all the anodization worn off. Right before we take off or when we're on approach for landing we'll either ask the tower for the "local altimeter" (which, in pilot-speak, means the barometric pressure at the airport) or we'll get the information from the A.T.I.S. broadcast from the airport. Then we set the altimeter to that barometric pressure which allows it to display the correct altitude.

 

Depending on the flying conditions and the terrain we're flying over, this routine might be repeated many times throughout a flight to correct for differences in the local barometric pressure. This is important when we're airborne if we want to remain comfortably above local obsticles like radio antennas and mountains or fly at the correct altitude in a controlled airspace. It's also important when we're taking orders from a tower of flight controller 'cause when they say decend to 4000 feet and maintain, they mean 4000 feet!

 

i was thinking the same thing, if you have an altimeter you might as well set it.

I won't argue that, but it's important to understand that it won't stay accurate for long, especially in an unstable weather pattern. And keeping it set is almost as frustrating as trying to own the latest and greatest GPSr.

 

Have the manufacturers totally eliminated satellite based altitude capability? I seem to see more and more of these type posts where it seems as though they have. Why? I can't even hazard a guess.

Most haven't. The barometric altimeter is only a feature on some high-end GPS units and they're typically a supplemental option to GPS altitude (calculated by satellite triangulation). But given accurate and current local barometric pressure data, a barometric altimeter has a potential for greater accuracy than GPS altitude, especially with consumer-grade GPS units.

 

Pete

Edited January 3, 2010 by Curioddity