Performance of part union?

[eudoxos]

I use FreeCAD to compute surface of solid composed of a number of lightly overlapping spheres. The goal is to export triangulated external surface(s) of fused spheres (with the overlapping parts removed).



Spheres are around 1500 in number and I create them using generated script with these lines for each sphere:

Code: Select all

p=doc.addObject("Part::Sphere","par_1234")
p.Radius=0.004
P.Placement=Placement(Vector(0,1,2),Rotation(Vector(.4,.2,.4),56))

The script takes some time to process (around 1 minute). When I select all spheres and hit Part/Boolean/Union, FreeCAD eats 100% CPU but does not seem to produce any result until I kill it 5 minutes later.

Am I (not) doing something which slows the operation down or is this number of solids simply beyond what the OCC kernel can handle in a reasonable time? Is there some other way to get the result?

Thanks!

[DeepSOIC]

Hi!
OpeCascade's Booleans are slow. Trouble starts even with gears, that only have a few tens of teeth. This is not surprising this is taking forever to compute.
Try fusing them as shapes, one by one in a cumulative manner. So that you can make a progress bar. That can give you a feel of how long it's going to take.
something like...

Code: Select all

spheres = [obj.Shape for obj in App.ActiveDocument.Objects]
final_shape = spheres[0]
for sphere in spheres[1:]:
  final_shape = final_shape.fuse(sphere)
  #(insert progress-bar code here)

Part.show(final_shape)

[ulrich1a]

In order to get a result at all, I would follow DeepSOICs approach but with a modification. It will end as an complicated script.

Explained with two spheres. Sphere1 and Sphere2.
Take the Face from Spere1 and cut the Face with Sphere2 in order to get Face1_cutted.
Take the Face from Sphere 2 and cut the Face with Sphere1 in order to get Face2_cutted.
Put Face1_cutted and Face2_cutted into a List.
Create a Shell from this List.
Create a Solid from this Shell.

For more Spheres you need to generate all the cutted Faces from those Spheres and add the cutted Faces to the List.

This approach should work. I used the same approach to generate screws with a real thread on it.

Ulrich