Below water line/flood plain alt readings

[Tbonham27]

Anyone have simple insight on where our elevation readings on the apps come from or how they are measured? For example if flying over a man made body of water...what's the altimiter reading? Lake bottom or water line?
The last few feet of my property are designated flood plain and the 26 year old golf course as well, fairly large course. Is the current data most likely contour of the course? Natural low land before all the excavating?
My level to ground track across a 75 yard pond varies three points in a roll.. just curious. Thanks

 

[Nightwolf]

The altitude displayed is relative to the point of take off. Calculated by barometric readings I believe.

 

[Meta4]

Anyone have simple insight on where our elevation readings on the apps come from or how they are measured? ... Is the current data most likely contour of the course? Natural low land before all the excavating?
My level to ground track across a 75 yard pond varies three points in a roll.. just curious.

Apart from the VPS which can only work up to 10 metres high, the Phantom has no way to sense the ground below and no database to refer to.
Nightwolf has explained where the altitude data you see in the app comes from.

 

[Tbonham27]

Apart from the VPS which can only work up to 10 metres high, the Phantom has no way to sense the ground below and no database to refer to.
Nightwolf has explained where the altitude data you see in the app comes from.

I understand. I failed to share some info. I apologise. It was litchi waypoints reading diff over the plane flat water..those points fell under alt related to ground batch settings

 

[Richard R]

Are you using the terrain following feature in litchi? If so, the ground reference would be wherever the ground level was when the data was "surveyed" I know that maps made easy uses the NASA data that can be a couple of years old. If you are not doing TF, then as mentioned above, it makes no difference what you are flying over, altitudes are referenced to the Home Point. Now if you are flying in VPS mode and low enough, water is a tough surface for the VPS to handle. The data in the exif file for your photo will reference MSL altitude using the GPS signal.