Is there a MavLink field for msl altitude without using GPS?

ArduCopter Copter 4.7
1

I have a MavLink application in development.

The application is for a GPS denied quad-copter. Can a msl altitude be obtained using just the barometer? The altitude field initializes to “0” at the home point at start up. My application may have use for knowing actual msl altitude.

2

If you have the actual value of your home point (starting point) of your drone temporarly you can add the barometer reading to this value. But you must know the barometer reading is not only a function of the hight but also of the actual weather conditions. So it is changing over time.

2 Likes
3

Yea, perhaps with a script with home point MSL entry and then relative barometer after that as @Juergen-Fahlbusch suggests. If you have telemetry perhaps that value can be grabbed from the ground station.

1 Like
4

Hi @jstroup1986,

Perhaps it’s been covered in the replies above but in any case, the barometer’s altitude is normally added to the EKF origin and the origin can be set using a mavlink message (normally set by the user using the GCS) when the user or using a lua script. Once that is done the EKF should calculate the absolute altitude and it appears in the VFR_HUD mavlink message which most GCSs display.

best of luck!

5

Thanks @rmackay9 -

I’m working on an application for GPS denied operation. So there will be no way to get a reference altitude using the terrain map.

I was hoping that a raw barometric pressure was available - then a good guess could be made using standard pressure of 29.92 in-hg.

I’ll poke around a bit more and see what I can find. If I find anything interesting - I’ll report it here.

Thanks - Joe

6

It is available and it changes constantly. There is no “standard pressure” Not clear on what else you will find in this regard. Just look at any weather report… This is not a reference altitude metric.

7

In MP you can use the CTRL-F menu to set the QNH based on an altimeter setting from a local airport.

But… I tried to grab some screen shots at it errored on both my windows and linux systems so maybe not.

1 Like