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Author Topic: WGS84 UTM36S with EGM2008  (Read 181 times)

precision

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WGS84 UTM36S with EGM2008
« on: February 21, 2019, 04:21:37 PM »
Hello,

I trust you are well. I fly an Ebee Plus RTK, and it is geotagging images in WGS84. I am processing in Agisoft, and I would like my project to output as WGS84 UTM zone 36 S with EGM2008 for the Heights to ensure the Orthometric Heights are correct since the eBee only captures Ellipsoidal Heights.

I added the EGM2008-1 Model to the Geoids Folder in Agisoft, however I cannot seem to get the workflow right to ensure it processes accordingly. The single time i got it to work the heights were out by 10 metres or so in comparison to the check point i used. Is there a manual explaining how to use Geoids in Agisoft thats somewhere i can't find it?

Appreciated;

Owen

Alexey Pasumansky

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Re: WGS84 UTM36S with EGM2008
« Reply #1 on: February 21, 2019, 10:20:09 PM »
Hello Owen!

Have you tried to use Convert option after processing the alignment in WGS84 coordinates and then select the custom coordinate system that can be created by editing WGS 84 / UTM zone 36S system by adding EGM2008 in the Vertical CS field.

Maybe the following instruction would be helpful to you for the custom coordinate system creation:
https://agisoft.freshdesk.com/support/solutions/articles/31000148332-how-to-use-height-above-geoid-for-the-coordinate-system
Best regards,
Alexey Pasumansky,
AgiSoft LLC

precision

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Re: WGS84 UTM36S with EGM2008
« Reply #2 on: February 22, 2019, 04:57:58 PM »
Hi Alexey,

Thank you for this. I managed to get it to work... however I am noticing a difference of around 20cm in the Z value when i check my Checkpoints Elevations. This error is still present even if i process in simple straightforward Ellipsoidal Heights.... eMotion 3 and my Ebee Plus RTK had said my RTK Accuracy was 2.5cm so i am a bit confused that i am finding the Z value so different on the checkpoints. Might there be something else I need to check?

Appreciated! :)

Alexey Pasumansky

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Re: WGS84 UTM36S with EGM2008
« Reply #3 on: February 22, 2019, 06:11:05 PM »
Hello Owen,

If the elevation difference is observed across the whole area and is fixed, it may be a result of inaccurate focal length estimation during the autocalibration operation.
Best regards,
Alexey Pasumansky,
AgiSoft LLC

precision

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Re: WGS84 UTM36S with EGM2008
« Reply #4 on: February 22, 2019, 06:30:37 PM »
The difference is not consistent though. On one checkpoint the difference is 5cm, on another its 8.5cm, another is 13.5cm and another is 15.1cm...

precision

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Re: WGS84 UTM36S with EGM2008
« Reply #5 on: February 25, 2019, 11:40:39 PM »
Hi Alexey,

I guess the easiest thing to ask is how do we input our images as WGS84 as they come from our eBee Plus RTK, and then process the outputs to be WGS84 UTM 36 South, but with a manual input of the Height Above Geoid amount. For example, in this area the Government specifies an adjustment of 10.370m to calculate from Ellipsoid Height to Orthometric Height, how can I add that manually rather than using an actual Geoid Model from the menu...

Thanks! Owen