Is there a collision detection method for meshes?

[Boehm92]

Hi,

i want to difference multiple machining features from a cube randomly. For example, i want to difference a 10mm and 5mm drill hole from the cube. If i substract first the 10mm drill hole and then the 5mm at the same place, there will be an exception because there is no mesh i can difference the 5mm from.

So, i would like to randomly place the 10mm and 5mm drillholes first and check if both colide. If so, i unite both with the boolean operation and then difference them from the cube.

Therefore, i need a method to check, if both drillholes are colliding after randomly placing them. Is there such a function?

Kind Regards,
Stefan

[jimy-byerley]

Hello @Boehm92 !

About drilling

I'm not sure to understand the need of an intersection-check function in this case, as there is nothing wrong in performing a boolean union or difference when the meshes are not intersecting. In case of non intersecting meshes, a union will simply concatenate them, resulting in one mesh containing 2 islands, a difference will result in only the first mesh unmodified.
Here is an example of what I understand of your case:

from madcad import *

def cylinder(bottom:vec3, top:vec3, radius:float) -> 'Mesh':
	direction = top-bottom
	return extrusion(direction, 
             flatsurface(wire(Circle((bottom,normalize(direction)), radius)))
             .flip())

cube = brick(width=vec3(1))
c1 = cylinder(O, Z, 0.2)
c2 = cylinder(vec3(1,0,0.1), vec3(1,0,0.9), 0.2)
c3 = cylinder(vec3(0.2,0,0.2), vec3(0.2,0,0.8), 0.15)

# both following solutions are valid:
result = difference(difference(difference(cube, c1), c2), c3)     # performing drill holes one by one
result = difference(cube, union(union(c1, c2), c3))      # making a union of the drills and then performing the holes all at once

• The cylinders
  

• The result
  

About intersection-check

For the question of intersection-check itself, I might have a solution, but not very efficient ... The lowest level intersection function available in the API is madcad.boolean.cut_mesh(). boolean operation on meshes are built on top of this function.

However it is meant to actually compute intersections, so it will compute all the intersections before returning, instead of stopping at the first existing intersection found, as a good intersection-check would do.
Also it is an in-place operation (altering the input mesh), so not suited for checks.

If you really need to check for intersections (or possible intersections) between meshes, I would advice creating dedicated functions, using for instance the following techniques:

• bounding-box intersections check (to check for possible intersections)
• convex hull intersection check (to check more precisely for possible intersections)
• search for intersections using spacial hashing (to quickly access potentially intersecting faces)
• return at the first intersection found
• eventually use pybullet to check in a vast amount of meshes

If you really need such a function I think I could hack something 🤔

[Boehm92]

Thanks again for the fast respons. I'm greatfull for your great support!

In your example the cylinder is positioned in the cube the second time. There, i also dont get the "AttributeError". But when i move the cylinder outside the cube (in empty space), just then i get the "Attribute Error".

from madcad import *

cube = read('Cube.stl')
cube.mergeclose()
cube = segmentation(cube)  # segmentation is for aspect, when importing STL files

cylinder = read('cylinder.stl')
cylinder.mergeclose()
cylinder = segmentation(cylinder.transform(vec3(1e-3)))  # segmentation for aspect, and small offset between surfaces

first_time_diff_cylinder = difference(cube, cylinder)

cylinder = cylinder.transform(mat3(0.9, 0.9, 0.9))
cylinder = cylinder.transform(vec3(-3, -3, 0))

show([cube, cylinder, cylinder])

second_time_diff_cylinder = difference(first_time_diff_cylinder, cylinder)

[jimy-byerley]

Hi @Boehm92 , well you might have an old version of the module don't you ?
Event when I reinstall the pure v0.11 from pypi I'm unable to reproduce the AttributeError
what's the result of pip show pymadcad ?

[jimy-byerley]

If pip doesn't show you pymadcad == 0.11 I would suggest upgrading it using pip install -U pymadcad

[Boehm92]

That did the trick. I allready tried to update the package, but for some reason it stuck by 0.10.2. I created a new interpreter and it worked.

Thanks so much and sorry for all the trouble!

[jimy-byerley]

No problem, you are welcome :) I'm glad to help