My team and I ordered a GPS unit from DIYdrones (GS407) for replacement in our Ardupilot/Easystar setup (The first got trashed in an unfortunate meeting with a building at 100ft.) The unit was ordered to be Ardupilot compatible, and would not plug and play (Would not lock). After some digging around and analysis in uCenter we found out that the gps did indeed have a lock. We found the configuration code (attached) somewhere on the DIY Drones site and uploaded that to the GPS, and everything seemed to be functional, except for the altitude, the altitude is technically correct (at about 310m above sea level) on the ground, but after some further research, it appears that the system thinks that it is 310 meters above the ground, not above sea level, so when we told it to maintain a height of 150 meters... it took a nosedive to the ground before we could recover it. My question is: Is there a GPS configuration setting that I missed when configuring the GPS, or is there a setting in the header file that I need to change? I have looked for a while now, and am a bit overwhelmed with the configuration options for the gps module.
When you save your home position before takeoff the Ardupilot saves the altitude and subtracts this from the ASL from the GPS. If you don't do this the saved altitude will be sea level.
Another important issue is that you should never trust on GPS altitudes due it might suddenly jump over 100 meters in matter of minutes. Yes some areas you can get really nice accurate altitude but then again some areas not. So if you rely on GPS altitude, be careful.
GPS altitude is reported as height above the reference geoid (a somewhat idealized Earth). That is "sort of" sea level but not exactly.
To report height above ground, the little feller would have to have contained within it a topographical map of the world. There *may* be big granddaddy GPSs that have that, but the little modules we use have nowhere near enough memory to hold all that, even at low resolutions. So none will report AGL.
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To report height above ground, the little feller would have to have contained within it a topographical map of the world. There *may* be big granddaddy GPSs that have that, but the little modules we use have nowhere near enough memory to hold all that, even at low resolutions. So none will report AGL.