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P1 > Overlap issue
844 7 2023-5-12
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AR_AirPrecision
Captain
Flight distance : 2634961 ft
Belgium
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Hello!

We configured a mapping mission with overlap 80/80 + buffer 35m. Flight speed 7m/sec @90m AGL, GSD 1cm/px

After we flew the mission, the calculated overlaps end up much lower than configured : 72/73 ( which create issue with AI/ML processing of customer )


Any idea what could cause this? The mapping was above a field of approx 10x400m ( main reason we added 35m buffer ).


Regards,


AR
2023-5-12
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JesseG
lvl.3
Flight distance : 19941 ft

United States
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Are you sure the M300 was flying at the planned 90m AGL? On my last flight(2 weeks ago after the recent firmware update) using DJI Pilot2 I planned a flight for 250ft AGL and it flew at 215-220ft AGL. Thats nearly a 10 meter difference and caused me to refly the site on a future visit. I have been using UGCS for flight control for years but wanted to try DJI pilot2 again due to being in very close proximity to an airfield and UGCS does not support airsense for real time manned aircraft detection. I have since switched back to using UGCS exclusively.  I would compare your exif data to that of one of your ground control points to see what the altitude the M300 was actually flying.
2023-5-17
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AR_AirPrecision
Captain
Flight distance : 2634961 ft
Belgium
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JesseG Posted at 5-17 15:59
Are you sure the M300 was flying at the planned 90m AGL? On my last flight(2 weeks ago after the recent firmware update) using DJI Pilot2 I planned a flight for 250ft AGL and it flew at 215-220ft AGL. Thats nearly a 10 meter difference and caused me to refly the site on a future visit. I have been using UGCS for flight control for years but wanted to try DJI pilot2 again due to being in very close proximity to an airfield and UGCS does not support airsense for real time manned aircraft detection. I have since switched back to using UGCS exclusively.  I would compare your exif data to that of one of your ground control points to see what the altitude the M300 was actually flying.

Thanks for advices, will check that.
I was using "terrain follow" I wonder if that could have created the issue...but the terrain was flat-ish ( Belgium is flat )
2023-5-19
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dim.kyr
lvl.2

Switzerland
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AR_AirPrecision,

Did you sort out the above-mentioned issue with P1 overlap?
1-31 07:43
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AR_AirPrecision
Captain
Flight distance : 2634961 ft
Belgium
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dim.kyr Posted at 1-31 07:43
AR_AirPrecision,

Did you sort out the above-mentioned issue with P1 overlap?

Yes, terrain follow was the problem. I don't use it any more unless terrain is not flat.
1-31 08:16
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MIDIC
lvl.3

Germany
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AR_AirPrecision Posted at 1-31 08:16
Yes, terrain follow was the problem. I don't use it any more unless terrain is not flat.

Is the DJI TerrainFollow function using ellipsoidal hights?
2-5 01:54
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Panph
Second Officer
Flight distance : 5322589 ft
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Italy
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MIDIC Posted at 2-5 01:54
Is the DJI TerrainFollow function using ellipsoidal hights?

no, above sea level, i suppose geoid EGM96
2-5 02:29
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MappingPro
lvl.3
United States
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MIDIC Posted at 2-5 01:54
Is the DJI TerrainFollow function using ellipsoidal hights?

According to Chat GPT

DJI is using ASTER GDEM (Global Digital Elevation Model) files for terrain following altitudes, the altitude type provided would likely be ellipsoidal height.

ASTER GDEM is a global digital elevation model produced by NASA and the Ministry of Economy, Trade, and Industry (METI) of Japan. It represents the Earth's surface as an elevation grid referenced to the WGS84 ellipsoid. Therefore, altitudes derived from ASTER GDEM data would typically be ellipsoidal heights.

Ellipsoidal heights are measured from the reference ellipsoid, providing the elevation above the mathematical model of the Earth's shape. They do not take into account variations in the Earth's gravity field and may differ from orthometric heights, which represent elevations above a geoid or mean sea level.

It's worth noting that while ASTER GDEM provides a global elevation model, its resolution and accuracy may vary depending on the location and terrain characteristics. Users should be aware of the limitations and potential inaccuracies associated with using ASTER GDEM data for altitude measurements in critical applications.
2-6 16:53
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