dane_ Posted August 3, 2020 Share Posted August 3, 2020 How do I place a symbol on a NURBS surface normal to the surface. Eg. A post on a arched bridge. I can find the normal vector at the point with vs.EvaluateNurbsSurfacePointAndNormal(surfaceH, u, v) I assume I can somehow locate the symbol with vs.SetEntityMatrixN( objectHandle, u , v , w, offset) How do I get the u,v and w vectors? or calculate the angels from the normal vector to use vs.SetEntityMatrix(vs.LNewObj(), *wp) I can get it to work with: vs.SetWorkingPlaneN(*pt, *norm, *uVec) wp = vs.GetWorkingPlane() vs.Symbol("post", (0,0), 0) vs.SetEntityMatrix(vs.LNewObj(), *wp) The symbol is placed in document space not the working plane but the GetWorkingPlane function returns the angle in degrees needed for SetEntityMatrix There must be a better way I am missing... I am not sure why vs.SetEntityMatrixN needs different inputs to vs.SetWorkingPlaneN Any pointers appreciated. Thanks Quote Link to comment
dane_ Posted August 5, 2020 Author Share Posted August 5, 2020 To follow up the following works: def placeSymbolOnSurfaceAlignedWithUVDelta(u,v, surfaceHandel, symbolName, du,dv): # get the 3d point and vector normal to the surface ptExists, pt, normal = vs.EvaluateNurbsSurfacePointAndNormal(surfaceHandel, u, v) if ptExists: # place the symbol at (0,0,0) then move it. Assumes symbol is defined to be aligned by its insertion point vs.Symbol(symbolName, (0,0), 0) symbolHandel = vs.LNewObj() # create an orientation vector using a point either side of u,v (u-du,v-dv), (u+du,v+dv) where du,dv are small compared to the surface curvature and their relative magnatudes define the orientation in the u,v plane eg u=0,v=0.0001 will result in a vector in the direction of v at the point orentation = tuple(map(sub, vs.EvaluateNurbsSurfacePointAndNormal(surfaceHandel, u+du, v+dv)[1], vs.EvaluateNurbsSurfacePointAndNormal(surfaceHandel, u-du, v-dv)[1])) # this is a good estiment but it fails because it is not exactly orthogonal to the normal vector. Correct by projecting onto the plane tangent to the surface at u,v uVec = tuple(map(sub,orentation, [vs.DotProduct(orentation,normal)*i for i in normal])) # w-vector is the normal vector wVec = normal # we know the other 2 and they are all orthogonal so v-vector is the cross product of u x w vVec = vs.CrossProduct(uVec,wVec) # offset is the 3d point because the symbol is currently at 0,0,0 offsetVec = pt vs.SetEntityMatrixN(symbolHandel, uVec, vVec, wVec, offsetVec) return symbolHandel Quote Link to comment
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