Help Needed with Projecting Points onto Mesh Along Specified Axis Using MeshLib

[doknicilija98]

Hello,

I am new to MeshLib and need assistance with projecting points onto a mesh along a specified axis.

Specifically, I have the X and Z coordinates of a point and need to find the minimum Y such that the point (X, Y, Z) lies on the mesh. After determining this point, I need to place it inside a Contours3f object. I attempted the following approach, but encountered issues with data types:

for i, x in enumerate(path):
    point = mm.Vector3f(X, -50, Z)  # -50 acts as a negative infinity
    trajectory[0][i] = mm.findProjection(point, mesh).mtp  # trajectory is Contours3f object 

I received the following error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[35], line 8
----> 8 trajectory[0][i] =  mm.findProjection( point, mesh).mtp

TypeError: __setitem__(): incompatible function arguments. The following argument types are supported:
    1. (self: meshlib.mrmeshpy.Contour3f, arg0: int, arg1: meshlib.mrmeshpy.Vector3f) -> None
    2. (self: meshlib.mrmeshpy.Contour3f, arg0: slice, arg1: meshlib.mrmeshpy.Contour3f) -> None

Invoked with: <meshlib.mrmeshpy.Contour3f object at 0x0000022851CEC470>, 0, <meshlib.mrmeshpy.MeshTriPoint object at 0x0000022851CCE3B0>

Additionally, I would like to project the point that is on the mesh to the edge of the mesh along some axis.

Could someone please help me with the following:

1. Correcting the code to properly project points onto the mesh.
2. Ensuring the projected point can be placed into a Contours3f object.
3. Projecting the point that is on the mesh to the edge of the mesh along a specified dimension.

Thank you for your assistance!

[Grantim]

Hello!

findProjection function finds closest point on mesh in MeshTriPoint type, as far as you need to project in single direction you should use rayMeshIntersect

for i, x in enumerate(path):
    point = mm.Vector3f(X, -50, Z)  # -50 acts as a negative infinity
    line = mm.Line3f(point,mm.Vector3f(0,1,0)) # ray for intersection
    # point on mesh, note that mm.rayMeshIntersect(mesh,line) may return None if mesh was not intersected with the ray
    meshPoint = mm.rayMeshIntersect(mesh,line).mtp # (1)
    cartesianPoint = mesh.triPoint(meshPoint) # (2) cartesian point for Contours3f 
    trajectory[0][i] = cartesianPoint  # trajectory is Contours3f object 

Do you mean mesh boundary by edge, or edge of mesh triangulation, could you please provide some images and/or more details about 3rd question?

[doknicilija98]

Hello,

Thank you for your answer, the code worked. Regarding the meaning of "edge" I meant boundary. For example, I have point 1 and I want to find want 2.

I hope this helps

[Grantim]

Thanks for explanation.
This looks a little bit tricky, if I got you correctly, you need lowest point of plane section. (Plane that goes through P1 and parallel to Y direction and surface normal in P1).

# lets say we have p1 as mm.MeshTriPoint to simplify code

# setup plane
plane = mm.Plane3f()
plane.n = mm.cross(mm.Vector3f(0,1,0),mesh.normal(p1))
plane.d = mm.dot(plane.n, mesh.triPoint(p1) )

# extract sections
sections = mm.extractPlaneSections(mesh,plane)

# find section point with max Y component
minSection = mm.EdgePoint()
maxY = -1e100 # minus infinite
for path in sections:
    for edgePoint in path:
        p = mesh.edgePoint(edgePoint)
        if (p.y > maxY ):
            maxY = p.y
            minSection = edgePoint