Wednesday, October 22, 2008

GPS Comparisons Auto

By Hodges Rios

Why have an electronic compass?
A GPS receiver discerns your position on the surface of the earth by measuring the length of time it takes to receive signals from satellites. It cannot, however, tell what direction you are facing while standing still (or moving slowly). So if you are navigating to a waypoint, your GPS can only point you in the correct direction once you are moving. This is where an electronic compass comes in handy. It can tell what direction you are facing, even while standing still.

Why have a barometric altimeter?
Quite simply, the primary reason you would want a barometric altimeter in a handheld GPS is for more accurate elevation readings. This is especially useful for bikers, hikers and atheletes in training. You can use the resulting data to track your progress and maintain an accurate record of your trips. A barometric altimeter can also help you accurately place your location on a topo map. Furthermore, you can use the altimeter to forecast weather trends.Quite simply, the primary reason you would want a barometric altimeter in a handheld GPS is for more accurate elevation readings. This is especially useful for bikers, hikers and atheletes in training.

Why is there an Abrupt Elevation Change?
During that time you experienced your max Uphill Grade, Max Ascent and Descent Rate. You finished your activity at the same place you started, but the elevation profile shows you finishing over 200 feet higher than where you started. Your altimeter was auto-calibrating using the GPS information as a reality check to correct the change in barometric pressure since last calibration. I love this feature, but it is causing some headaches.Now that SA (Selective Availability) has been turned off, the general answer to this is Yes. GPS altitude is at least as accurate as the reading from a barometric altimeter. However, to determine altitude a GPS MUST be receiving information from at least three satellites and the more it is tracking, the better. If you want more information on this subject, there have been NUMEROUS postings on the rec.aviation.soaring and sci.geo.satellite-nav newsgroups.

How accurate are the heights or depths?
The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter. Radar altimeters are estimated to have an error of 2-5% of the altitude (Richard Hansen, PRJ, Inc., written communication). Barometric altimeters are quite accurate, but are typically operated in an uncorrected mode.During that time you experienced your max Uphill Grade, Max Ascent and Descent Rate.

How accurate are the heights or depths?
The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter. Radar altimeters are estimated to have an error of 2-5% of the altitude (Richard Hansen, PRJ, Inc., written communication). Barometric altimeters are quite accurate, but are typically operated in an uncorrected mode.The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter. Radar altimeters are estimated to have an error of 2-5% of the altitude (Richard Hansen, PRJ, Inc., written communication). Barometric altimeters are quite accurate, but are typically operated in an uncorrected mode.

How accurate are the heights or depths?
The aircraft vertical position was determined using the navigational positioning equipment on the aircraft, which were radar altimeter and barometric altimeter. Radar altimeters are estimated to have an error of 2-5% of the altitude (Richard Hansen, PRJ, Inc., written communication). Barometric altimeters are quite accurate, but are typically operated in an uncorrected mode.Some high-end GPS devices offer barometric pressure to obtain a measurement for elevation when signal reception is not very good. The result is that you will have a smoother elevation profile in the Dashboard and Map Player. Without an altimeter, the GPS assumes your elevation is not changing when the signal goes bad. This results in a blocky elevation profile.

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