Originally Posted by mustafagander
A further question, of course, is whether the altitude so derived is accurate. It seems to me that, given the GPS unit's onboard database size limits, there is little chance that relief data is available to make this altitude even close to reality.
A good point.
I'm not intimately familiar with the GPS system, but from it's principle of operation, it would seem that it's altitude capability is just as accurate as it's lateral positioning. I would think (think, that is!) that the biggest source of inaccuracy would be the charts. We all know that by now, our plain old 2D charts are very accurate, but how accurate is the terrain elevation data? Not compared to adjacent terrain, but in relation to the 3D universe the GPS reciever works in? Again, these are merely thoughts...
Edit: reading through your post again, I see that's pretty much what you were saying anyway. Bedtime for me!
