How to build solid directly from non-planar faces?

[GarryBGoode]

Hello!

I'm working on importing manim objects to CadQuery.
Manim objects are built from 4-point Bezier curve segments, so after figuring out how CQ likes its b-splines, it should be possible and not too hard...

My problem is that I can't find a way to directly build a solid from non-planar surface elements.
I tried constructing Edges and then a Wire from those, but then the Face class won't let me create it for not being planar :(

Here's an example code (needs manim):

import manim as mnm
import cadquery as cq
import numpy as np

cyl = mnm.Cylinder()

edges = []
for k in range(0,cyl.submobjects[0].get_num_curves()):
    points = cyl.submobjects[0].points[4*k:4*k+4,:]
    vectors = [cq.Vector((points[k,0],points[k,1],points[k,2])) for k in range(4)]
    tangent_vals=[(points[1,:]-points[0,:])/np.linalg.norm(points[1,:]-points[0,:]),
                  (points[3,:]-points[2,:])/np.linalg.norm(points[3,:]-points[2,:])]
    tangents = [cq.Vector((p[0],p[1],p[2])) for p in tangent_vals]

    edges.append(cq.Edge.makeSpline([vectors[0],vectors[3]],tangents, scale=False))

result = cq.Wire.assembleEdges(edges)

show_object(result)

result = cq.Face.makeFromWires(result)

[michaelgale]

While I can't provide a working implementation of what you're trying to achieve, I would consult the makeSplineApprox classmethod in the Face class or the interpPlate classmethod in the Solid class. The Face method can be used to generate multiple faces which can then be stitched together into a Shell and then into a Solid. The interpPlate method can directly yield a solid object representing a finite thickness plate.

At quick glance it appears the interpPlate method can be provided with either a list of edges or a list of 3D points. This method generates a solid which best approximates the surface described by the edges or points.

[GarryBGoode]

Thanks!
interpPlate looks promising, allegedly it returns a face when the thickness is 0.
Just for some reason I can't feed it this list of Edges, nor the assembled Wire, nor a list of Wires.

I'm also not a fan of interpolations when I already have spline patches. I know under the hood everything must be some form of spline patches... just lemme at 'em.
In the end I might need to evaluate a number of points from the manim splines, feed the points to the other approximator and hope the result is close enough.

And it's got a deprecation warning, interpPlate will be removed. I wonder what's up with that?

[adam-urbanczyk]

What is your real question? If you want to build a solid from faces, use Shell.makeShell and then Solid.makeSolid.

[GarryBGoode]

In the end I want to build a Solid with curved surfaces from splines that I calculate myself. The actual end goal is to make a gear generator.
Yes I wanted to make Faces and then Shell and then Solid.

As of yet I can't make a Face.

Face.makeFromWires() is complaining it's not planar. The interpPlate method is a bit confusing, the documentation says it can take a list of edges or wires but I haven't been able to make it work with wires.

If you can provide an example where interpPlate works on a wire or edges that would be great.

I am hesitant to use the approximation methods, eg. using interpPlate with points or makeSplineApprox cause I want full control over the shape, and I would like to avoid reverse engineering the quirks of the approximation.

[adam-urbanczyk]

Ok, the title of the post does not reflect your question then. Do you actually have the B-spline surface, or do you only have edges?

In the first case you'll need to use OCP/OCCT directly. In the second case you can use indeed interplate or better Face.makeNSidedSurface.

cadquery/tests/test_cadquery.py

Line 5587 in 3451007

def test_makeNSidedSurface(self):

[GarryBGoode]

OK, feels like I'm almost there. I was able to make the surfaces with Face.makeNSidedSurface. Then I converted them to a shell with Shell.makeShell.

Still, Solid.makeSolid does not take the resulting shell from the previous operations.
Visually it looks OK, so I don't know what goes wrong here.

TypeError: SolidFromShell(): incompatible function arguments. The following argument types are supported:
    1. (self: OCP.ShapeFix.ShapeFix_Solid, shell: OCP.TopoDS.TopoDS_Shell) -> OCP.TopoDS.TopoDS_Solid

import cadquery as cq
import numpy as np

cyl = mnm.Cylinder()
faces = []
for mob in cyl.family_members_with_points():
    edges = []
    for k in range(0,mob.get_num_curves()):
        points = mob.points[4*k:4*k+4,:]
        vectors = [cq.Vector((points[k,0],points[k,1],points[k,2])) for k in range(4)]
        tangent_vals=[(points[1,:]-points[0,:])/np.linalg.norm(points[1,:]-points[0,:]),
                      (points[3,:]-points[2,:])/np.linalg.norm(points[3,:]-points[2,:])]
        tangents = [cq.Vector((p[0],p[1],p[2])) for p in tangent_vals]
        edges.append(cq.Edge.makeSpline([vectors[0],vectors[3]],tangents, scale=False))
    
    faces.append(cq.Face.makeNSidedSurface(edges,[]))
    
result = cq.Shell.makeShell(faces)
show_object(result)
result = cq.Solid.makeSolid(result)

[GarryBGoode]

OK, so I guess I found the answer, back here to report...

The issue was more with the topology, the top and bottle circle had 8 segments, the sides had something like 24 segments around the circular surface.
I think the kernel could not stitch it together into a nice shell.
When I changed the sides to be low res and have only 8 segments tangentially, it worked.