photogrammetry to CAD

[thschrader]

From the customer we get a photogrammetry-scan (with a drone) of a radio-tower.
The file is a 957 MB obj-mesh (including material/picture files).
Order: use the existing mesh as construction-reference for additional steel-parts.

With cloudcompare/FreeCAD I can reduce the mesh to the relevant part.
But the mesh is far to rough. From a previous project at this tower I know the dimensions
of some steel parts. When making an overlay with the mesh, you can see that the scan cant
be used for further work. I used “instantmesh” to produce a quad-mesh. Looks more
detailed, but doesnt help. The computation is RAM-intensive, at minimum 16 GB RAM necessary.

My solution would be to do an additional drone-run with a much higher resolution.
Which means I must fly near by the frame, above the platform, without seeing the drone.

Has anybody experience with such projects?
What drone/camera would you suggest?
Is a predefined/automatic flight possible (I am not a pilot)?
I need a scan-resolution of 5 mm minimum. Is that possible?

Comments welcome

frame.FCStd

(614.73 KiB) Downloaded 22 times

https://github.com/wjakob/instant-meshes
http://www.danielgm.net/cc/release/

test001.JPG (82.54 KiB) Viewed 632 times

test002.JPG (86.25 KiB) Viewed 632 times

[saso]

You would probably need a laser scan for such high precisions... And if you need it just for reference why using the mesh, why not just the point could?

[Willem]

A while ago there was someone using photogrammetry for reconstruction a historical racing boat. See https://forum.freecadweb.org/viewtopic.php?t=27770

[thschrader]

... And if you need it just for reference why using the mesh, why not just the point could?

I agree, good point.
At the moment we only get the mesh from the customer.
But there must exist the point cloud as a base for the meshing.
The images from the radio-tower are analized via this portal,
which gives back the obj-mesh (and some other stuff...)
https://www.vhive.ai/telecommunications/

I played a little bit with COLMAP and my cellphone (as a camera).
https://colmap.github.io/

[jeno]

... And if you need it just for reference why using the mesh, why not just the point could?

I agree, good point.
At the moment we only get the mesh from the customer.
But there must exist the point cloud as a base for the meshing.
...

Are you looking for this?

Regards

[thschrader]

...
Are you looking for this?
...

Yes, thanks a lot.
You can use the points for measurement, with arch-wb, line-tool.
I wonder how you created a real point object. I part-wb I selected the obj-mesh in the
tree and used "Create points object from mesh" (the black points).
But export as asc-file gives an error:
'Tile_1_nur_Mast_pts' is not a point object, export will be ignored.

This week our customer gives me an account for the vHive-portal (and a drone ).
I will try to get/generate a more precise mesh/point-cloud.

points.JPG (86.02 KiB) Viewed 363 times

[wmayer]

I wonder how you created a real point object. I part-wb I selected the obj-mesh in the
tree and used "Create points object from mesh" (the black points).

That's the wrong function because it creates a shape with vertexes. You have to switch to the Points workbench and use the function there.

[jeno]

...
Are you looking for this?
...

Yes, thanks a lot.
You can use the points for measurement, with arch-wb, line-tool.
I wonder how you created a real point object....

Hi Thomas,
I saved the mesh with the help of the mesh workbench as stl. I opened it in meshlab and saved the vertices of the mesh as xyz file.

Kind regards

[wmayer]

As said you can do the same with the function "Convert to points" in the Points wb. When invoking it a dialog comes up asking for the maximum distance and here you can enter any value because for a mesh its vertices are used (no sub-sampling is done).

The advantage of this function is that it also delivers a normal per point which might be useful in the further post-processing. You can see the existence of the normals when you set the display mode to Shaded because then you get almost the same visual representation as with a mesh.

When you export the point cloud and want to keep the normals then use the formats PLY or PCD.

[thschrader]

How to scale a point object?
Treestump has ca. 60 cm diameter in reality, cube size 2 mm!
Photogrammetry:
60 images with cellphone around stump, ply-file (100 MB) generated with visualSFM
and imported in FC and Cloudcompare.
http://ccwu.me/vsfm/
Goal: scan steel-structures, import in FC as design-reference for additional parts.
I have done this to find a workflow.
Advice welcome. Especially about the general precision of photogrammetry.

treestump.JPG (80.33 KiB) Viewed 170 times