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Author Topic: Cleaning Up Mesh Model In CAD  (Read 219 times)

jazzyj

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Cleaning Up Mesh Model In CAD
« on: October 16, 2018, 06:31:03 PM »
I've got a model of a warehouse roof.  There's objects on the roof like vents and such.  I need to use the model to design my solar panel array for the roof.  The mesh model that is exported from Photoscan is quite "busy"  is really only the best solution in this application is to load it into a CAD program and create a separate layer and essentially draft the outlines of all the objects I consider relevant (the edge of the roof and the 3D outlines of the objects on the roof?  It seems otherwise trying to decimate the point cloud and simplify the model does me no good as the photogrammetry output doesn't produce perfectly straight lines between the corners of the objects.


chrisd

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Re: Cleaning Up Mesh Model In CAD
« Reply #1 on: October 17, 2018, 03:48:06 AM »
There are some applications such a Leica Cyclone that will fit CAD geometry (primitive shapes like boxes, structural steel, cylinders, spheres, etc)  to scans automatically.

CloudCompare has some functionality in this area, although its not as capable as Cyclone.

jazzyj

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Re: Cleaning Up Mesh Model In CAD
« Reply #2 on: October 17, 2018, 03:54:22 AM »
I believe the only solution using photogrammetry is to export a GeoTiff, bring it into GIS software like QGis (or directly into CAD - any info on that out there?), then create a new layer to draft the shapes in 2D using the GeoTiff photo as your guide.  Then bring the model into CAD and the 2D outlines as another layer and at the verticle dimensions.  Everything is a box shape.  So even though the mesh model shows the rectangular boxes on the roof as round mounds you can use the top of the mount as the vertical dimension to extend the 2D outline of the footprint of the box into 3D space with the proper height.  Then basically just throw away the photogrammetry 3D model.

The photogrammetry models seems to be good for texture models, but as far as making precise measurements of objects in 3D space, it doesn't look to have a very good level of precision.  Whereas relative distance measurements between two points, especially in the horizontal plan on a GeoTiff, seem to be pretty darn accurate.  It's just the edges of objects with straight edges just aren't smooth.  I may experiment with Cyclone.

But in my opinion, the only way to really can a precise 3D mesh model of any object is using Lidar.