Is the GPS Altitude Accurate?
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. I encourage you to check them out. In addition, the newest generation of handheld GPS’ can now make use of the FAA’s Wide Area Augmentation System (WAAS) in the United States. Using WAAS, accuracies of less than 3 meters.
