When I extract frame metadata using vmeta-extract, the output altitude appears to be derived from GPS (WGS84).
When I look at the .json exported from the ground control station (flight metadata as opposed to frame metadata), altitude appears to be height above takeoff location. How is this value actually calculated? Is it just GPS differencing? Barometer?
My understanding is that true AGL can’t be calculated here without a DEM, correct?
Edit:
Product: Anafi USA
“software_version”:“1.7.7”,
“build_id”:“anafi-mark3-1.7.7”
SDK/Pdraw/vmeta built from GitHub yesterday. This is relevant to dev work because these values must be know to create MISB compliant video.
The output altitude is indeed ATO (Above Take Off), but the vertical measures from the GPS are not used in the altitude estimation. The height estimation is a fusion from several sensors when available (barometer, accelerometer, vertical camera, ultrasound range sensor).
We do not use DEM to evaluate the distance between the ground and the drone, it is estimated using ultrasound and/or vertical optical flow measurements. So it is quite reliable if the drone flies close to the ground (up to a few meters depending on speed and the type of ground) and the sensors are in range.
But if the sensors are out of range, the drone can’t “see” the ground, so the ground height estimate is frozen at the last known value and the ground distance estimate varies only with the absolute altitude, hence becomes less reliable as it doesn’t take into account eventual ground height variations.
I hope this answers your questions
Best regards,
Camille
The ground_distance value from frame metadata (vmeta-extract output) and the altitude value from the flight metadata both measure ATO (above takeoff) derived from various onboard sensor data.
It’s also important to note that while these values are calculated the same way, they are recorded on separate timelines (frame and flight respectively).
Confirmation or correction of this is much appreciated. Thank you!
The ground_distance value from frame metadata (vmeta-extract output) and the altitude value from the flight metadata both measure ATO (above takeoff) derived from various onboard sensor data.
ground_distance is not really ATO, it is the vertical distance between the ground and the drone. We estimate the ground height and the drone altitude, both ATO, and the difference between those two estimates gives the ground_distance
So the ground_distance value extracted from frame metadata is the drone’s estimate of true Above Ground Level altitude? Vertical distance above the physical surface of the earth. This is my original question, can AGL be calculated in some fashion without the use of a DEM?
That means the altitude value from the flight metadata is the Above Take Off elevation.
I realize that speed/surface types are important factors, but in your experience how high can the drone fly and still return accurate AGL values?