topic Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong) in ReCap Forum

Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

stewart_agnew_bamnuttall_co_uk — Mon, 14 Dec 2020 17:20:34 GMT

Hi all. I've been trying to process drone imagery into point clouds for importing into Civil 3D to create surfaces (track changes, calculate volumes & etc.) but I've been struggling to fully co-ordinate the point clouds I'm producing.

I've managed to import & assign (usually 5) GCPs in the recap process and I'm finding that the X & Y values are accurate enough, but the Z value is way off. In relative terms the Z value appears fine, as in my roof apex is correctly 12.1m above my FSL, but the absolute AoD is wrong. For example one of my GCPs is say 50.000 AoD but on my point cloud (in ReCap & Civ 3D) the same point on the cloud / model is -43.600 AoD.

How do I get the point cloud & any subsequent exports to feature the absolute AoD level instead of what appears to be a randomly assigned Z level? From what I've seen I can adjust the origin of the drawing but this seems like the wrong approach as the model starts at ~ -25.000 (tops of trees) and goes down to ~ -49.000 so I wouldn't even know what to adjust it to.

Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

Pointdump — Tue, 15 Dec 2020 01:20:06 GMT

Stewart,
What is "absolute AoD level"?
Dave

Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

barmanr — Tue, 15 Dec 2020 03:09:25 GMT

Hi @stewart_agnew_bamnuttall_co_uk ,

Are you using Vertical Datums? Because as of now we do not support vertical datums. I think neither does Civil 3D according to this thread: https://forums.autodesk.com/t5/civil-3d-forum/civil3d-vertical-datum/td-p/7334106

If you're using GCP's then the Z values should have been forced to the exact value. Will need to investigate further with regards to the dataset. Would it be possible to share the dataset and the gcp file so that I can run it directly with the Engine?

Warmest Regards,

Rishov Barman, Reality Capture

Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

stewart_agnew_bamnuttall_co_uk — Tue, 19 Jan 2021 16:19:04 GMT

Above Ordnance Datum (United Kingdom) 🙂 If my GCP is say 50.000 AoD then I want the point in CAD to show it as 50.000 as opposed to 0.000

Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

stewart_agnew_bamnuttall_co_uk — Tue, 19 Jan 2021 17:48:01 GMT

@barmanr I don't think the issue has anything to do with vertical datums - my issue is more to do with the second point you've made there. The Z values are not being forced to the exact value. I've attached a screengrab below. The majority of the pointcloud should be tying in with an approx. level of 48 - 58m but it's showing as -37 to -47m in recap, infraworks and civ 3D.

Happy to share datasets for some further assistance - what do you need?

Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

barmanr — Wed, 20 Jan 2021 06:51:40 GMT

Hi @stewart_agnew_bamnuttall_co_uk ,

Possible to share the images and the GCP.xml file you used in ReCap Photo. I will process the dataset again on my end and then validate accordingly? You can PM me the links.

Warmest Regards,

Rishov

Re: Drone Imagery to Civil 3D Surface (X = OK, Y = OK, Z = Wrong)

barmanr — Tue, 26 Jan 2021 11:32:03 GMT

Hi @stewart_agnew_bamnuttall_co_uk ,

What's the source coordinate system for the GCP's?

Warmest Regards,

Rishov