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RTK Height / Elevation value
915 7 2023-4-14
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FoxSTI
Second Officer
Flight distance : 11286 ft
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Hello, I did our first RTK flight connected to a cors network in my state. I am seeing that by using the RTK correction I am getting an elipsoidal elevation of 3ft. (in the controller) and in the photo metadata.  When processing this photos in DJI Terra, how can I get those elevatoins to be based on a datum like NADV88 for instance.

Thank you
2023-4-14
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LV_Forestry
Captain
Flight distance : 4726654 ft
Latvia
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https://forum.dji.com/forum.php?mod=viewthread&tid=288425&mobile=2
2023-4-14
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PaulKofi
Second Officer
Mexico
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Hi, you must apply the geoid file (difference between elipsoidal elevation and MSL height) to your RTK hts to get MSL. For example on California coast, geoid height is more than -108 ft, so actual MSL ht will be more than 111 ft...for 3 ft elipsoidal ht
2023-4-15
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FoxSTI
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Flight distance : 11286 ft
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Hi guys, thank you for the replies. I have being working hard the past few days to understand all the terminology and what is means. So yes I figured shortly after that I would need some sort of transformation For the heights / elevation.  Here is what I see in the controller during a hover test (a few minutes at 80' AGL)... I see that the RTK CORS network is reporting an elevation of -50ft and showing my RTK height at  3.95ft  (flying at 80 ft AGL.)

I spoke to the guys who manage the Cors network I am using and connecting to and they said that their elevations are transmitted according to Geoid-18 (orthometric?) and therefore I am guessing that the controller thinks those readings are elipsoidial (because that how DJI and other UVAs work in general)  and thus thinks I am somewhere in a cave. I also don't see a way to tell the controller what units the information is getting is in. Geoid 18 is in meters from what I researched.

The the drone is embedding information into the photos with the incorrect unit and incorrect point of reference. The photos show a Z value of 3.95 (ft?) across my dataset.
Am I correct so far?

Here what I am seeing in Terra and probably what I would see in Pix4D. It does have the TIF for geoid 18 (cross referenced from the 2nd post).My hope is that this would transform the data and give me good evelations, but I seem to keep getting the same negative number at the ground (When I measure a point in Terra).

I am wondering what I am doing wrong at this point, Should I set the units on my controller to meters as opposed to feet (that just came to mind) but then my AGL would be meters and that would really mess me up and my other pilots. Elevations where this particular missing was flow should be 4.5' - 6'


TERRA_1.jpg


TERRA_2.jpg

2023-4-15
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LV_Forestry
Captain
Flight distance : 4726654 ft
Latvia
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FoxSTI Posted at 4-15 08:23
Hi guys, thank you for the replies. I have being working hard the past few days to understand all the terminology and what is means. So yes I figured shortly after that I would need some sort of transformation For the heights / elevation.  Here is what I see in the controller during a hover test (a few minutes at 80' AGL)... I see that the RTK CORS network is reporting an elevation of -50ft and showing my RTK height at  3.95ft  (flying at 80 ft AGL.)

I spoke to the guys who manage the Cors network I am using and connecting to and they said that their elevations are transmitted according to Geoid-18 (orthometric?) and therefore I am guessing that the controller thinks those readings are elipsoidial (because that how DJI and other UVAs work in general)  and thus thinks I am somewhere in a cave. I also don't see a way to tell the controller what units the information is getting is in. Geoid 18 is in meters from what I researched.
[Image]
I have never been able to do a geoid transformation in Terra.  I haven't tried for a long time, or else I'm too dumb.  

So like that the RTCM messages are broadcasted in orthometric value?  Either it's a particular network that doesn't follow the standards, or you've come across a clown.  I'm leaning towards option #2.  

Correction messages (RTCM) are based on ECEF coordinates.  Msg 1005 & 1006.

You can send me a picture taken anywhere at ground level with RTK enabled.  I will be able to say what kind of altitude is recorded in the meta (ellipsoidal, I am 99.9% sure). And at the same time explain to you what transformation you have to perform.
2023-4-15
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FoxSTI
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Flight distance : 11286 ft
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LV_Forestry Posted at 4-15 10:14
I have never been able to do a geoid transformation in Terra.  I haven't tried for a long time, or else I'm too dumb.  

So like that the RTCM messages are broadcasted in orthometric value?  Either it's a particular network that doesn't follow the standards, or you've come across a clown.  I'm leaning towards option #2.  

That would be great. Can you please PM me your e-mail address?
2023-4-16
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FoxSTI
Second Officer
Flight distance : 11286 ft
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I think that I got it to work...
2023-4-16
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LV_Forestry
Captain
Flight distance : 4726654 ft
Latvia
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FoxSTI Posted at 4-16 16:23
That would be great. Can you please PM me your e-mail address?

You can you use google drive or something like that
2023-4-16
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