Papa Bear
New member
In spite of several postings in the past, I'm still confused about altitude readings from a typical (say Garmin) GPS.
My impression are:
1) The GPS can show altiude readings from the sattelite data which one might call "digital" altitude readings.
2) Many GPS units also have a barometric altimeter built in. Call this the "barometric" altitude reading.
3) I thought the purpose of the barometric reading was to sync on the digital altitude and give a continuous reading even when the sattelite signal is temporarily lost. Thus the barometric reading is only as accurate as the digital reading that it last synched up with.
4) The intrinsic accuracy of the digital altitude is no better, and perhaps a bit worse than the location accuracy, i.e. 10s of feet.
5) the intrinsic accuracy of the barometric reading is also not more than 10 feet, and it also suffers from drift (due to changing weather) and intial setting at a known altitude (or in this case synching with the GPS digital reading).
Please give your comments and corrections to these points. I'm going to buy one of these babies and I'd like to know what to expect.
This was brought to mind by a guy with a GPS we met on Fort last week who insisted that the more western knob was 3 1/2 feet higher than the second knob (with the old radio transmitter). I assumed at the time he was full of sh*t. My Suunto (accurate to not more than 10 feet) gave the same altitude for both knobs, and I believe without a hand level or surveying tools that's about the best any portable device will tell you.
Thanks
Pb
My impression are:
1) The GPS can show altiude readings from the sattelite data which one might call "digital" altitude readings.
2) Many GPS units also have a barometric altimeter built in. Call this the "barometric" altitude reading.
3) I thought the purpose of the barometric reading was to sync on the digital altitude and give a continuous reading even when the sattelite signal is temporarily lost. Thus the barometric reading is only as accurate as the digital reading that it last synched up with.
4) The intrinsic accuracy of the digital altitude is no better, and perhaps a bit worse than the location accuracy, i.e. 10s of feet.
5) the intrinsic accuracy of the barometric reading is also not more than 10 feet, and it also suffers from drift (due to changing weather) and intial setting at a known altitude (or in this case synching with the GPS digital reading).
Please give your comments and corrections to these points. I'm going to buy one of these babies and I'd like to know what to expect.
This was brought to mind by a guy with a GPS we met on Fort last week who insisted that the more western knob was 3 1/2 feet higher than the second knob (with the old radio transmitter). I assumed at the time he was full of sh*t. My Suunto (accurate to not more than 10 feet) gave the same altitude for both knobs, and I believe without a hand level or surveying tools that's about the best any portable device will tell you.
Thanks
Pb