KeyTakeoffLocationAltitude value inaccurate
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This is on a Mini 3 Pro, using MSDK 5.4. I am getting the value from KeyTakeoffLocationAltitude and it is very inaccurate. It's off sometimes by 25m (twenty five) and it is inconsistently inaccurate as well. I understand accuracy of this value may not be great, but here are my questions:
1. How does the drone produce this value? Is it from GPS? Is the method different across different models of drones (e.g. with RTK)?
2. Is the takeoff altitude value produced by the drone or RC? Does it use the device connected to RC-N1 or does it use location on RC Pro?
3. In what coordinate system is this value? Is it WGS84 or EGM? I.e. is it ellipsoid altitude or geoid true mean sea level altitude?
4. Does MSDK use any map elevation data to produce this value?
5. What could impact the accuracy of this value? Poor GPS signal? Anything else?
Thank you.
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For your questions: 1. The altitude data obtained by this KEY is the fusion data of multiple sensors such as GPS and barometer. If the aircraft has RTK, it is recommended to obtain the RTK altitude. 2. Produced by drone. It is the altitude of the aircraft not RC. 3. It is ellipsoid altitude of WGS84 4. No. 5. There are many factors that affect the accuracy, this value can only be used as a reference. If you want to get accurate altitude, please get it through RTK. -
So, if I may make a suggestion for you guys for the next version of MSDK and DJI Fly.
If you're familiar with aviation then you know that barometric altimeters need to be calibrated at the start and during flight. In manned flight, altimeters are calibrated at lower altitudes from information provided by the tower or from ATIS. They will typically say something like 29.92 and then the pilot enters that to calibrate the altimeter. At higher altitudes (i.e. flight levels) they just use default calibration.
You might want to consider adding the ability to calibrate the barometric altimeter on the drone in DJI Fly in the next version and in MSDK. That way the value will be far more accurate.
GPS based altitude readings should have similar accuracy as lat/lng which is to say not great and depending on the number of satellites in range, on the order of a few meters at best.
Fusion is fine, but if one sensor is giving readings that are way off it defeats the purpose. I suspect barometer is your biggest issue because it's not calibrated. Since you provide this key, you might aw well make it useful and not just "for reference".
In terms of WGS84, I suggest that you guys bring in EGM2008 data into DJI Fly and undulate the altitude into MSL so it's more intuitive for users. Same can be done in MSDK. That way users don't have to undulate themselves.
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Thank you for your suggestion. Because the mini is a consumer drone, we will not design such a function for the time being. Because consumer drones are mainly used for aerial photography. For these users, it is not necessary to obtain accurate altitude values. For eneterprise drones, they are generally equipped with RTK. More accurate altitude can be obtained by RTK.
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