Creating nurbs surface using degree, control points, knots and weights

Rhino Developer rhino3dm
1

Can I get an example, please?
I’ve been looking at this example (on the bottom of the page):

Also, looking through the API: (NurbsSurface — rhino3dm 8.4.0 documentation)

There seems to be no SET functions only GET functions.

Also:
KnotsV.Count → no function Count
KnotsU.Count → no function Count

Here’s my unsuccessful attempt to translate this in CPython (rhino3dm)

def TST(is_rational = None, dim = None, u_degree = None, v_degree = None, u_cv_count = None, v_cv_count = None, u_knot = None, v_knot = None):
    if is_rational == None:
        is_rational = False
    if dim == None:
        dim = 3
    if u_degree == None:
        u_degree = 2
    if v_degree == None:
        v_degree = 3
    if u_cv_count == None:
        u_cv_count = 3
    if v_cv_count == None:
        v_cv_count = 5
    
    # make up a quadratic knot vector with no interior knots
    if u_knot == None:
        u_knot = [0.0, 0.0, 1.0, 1.0]
    
    # make up a cubic knot vector with one simple interior knot
    if v_knot == None:
        v_knot = [0.0, 0.0, 0.0, 1.5, 2.0, 2.0, 2.0]
    
    # Rational control points can be in either homogeneous
    # or euclidean form. Non-rational control points do not
    # need to specify a weight.
    CV = dict(((i,j),None) for i in range(2) for j in range(3))
    #print(CV)
    for i in range(0, u_cv_count):
        for j in range(0, v_cv_count):
            CV[i,j] = rhino3dm.Point3d(i, j,0)#i-j
    
    # creates internal uninitialized arrays for
    # control points and knots
    nurbs_surface = rhino3dm.NurbsSurface.Create(dim, is_rational, u_degree + 1, v_degree + 1, u_cv_count, v_cv_count)
    
    # add the knots
    for i in range(0, len(nurbs_surface.KnotsU)):
        nurbs_surface.KnotsU[i] = u_knot[i]
    for j in range(0, len(nurbs_surface.KnotsV)):
        nurbs_surface.KnotsV[j] = v_knot[j]
    
    # add the control points
    for i in range(0, nurbs_surface.Points.CountU):
        for j in range(0, nurbs_surface.Points.CountV):
            # SetControlPoint(self: NurbsSurfacePointList, u: int, v: int, cp: Point3d) -> bool
            nurbs_surface.Points.SetControlPoint(i, j, Rhino.Geometry.ControlPoint(CV[i, j]))
    
    if nurbs_surface.IsValid:
        model = rhino3dm.File3dm()
        model.Objects.AddSurface(nurbs_surface)
        #sc.doc.Views.Redraw()
        model.Write('test.3dm', 0)
    else:
        print('nurbs_surface.IsValid = False')

I’m a bit stuck here:
nurbs_surface.Points.SetControlPoint(i, j, Rhino.Geometry.ControlPoint(CV[i, j]))

SetControlPoint() function doesn’t exist in rhino3dm and there’s no object rhino3dm.ControlPoint() so I’m not sure what to do.

2

Hows this?

import rhino3dm

rational = False
dim = 3
u_cv_count = 6
v_cv_count = 6
u_degree = 3
v_degree = 3
u_order = u_degree + 1
v_order = v_degree + 1

ns = rhino3dm.NurbsSurface.Create(dim, rational, u_order, v_order, u_cv_count, v_cv_count)

#generate knots
ns.KnotsU.CreateUniformKnots(1.0)
ns.KnotsV.CreateUniformKnots(1.0)

#create points
for u in range(0, u_cv_count):
    for v in range(0, v_cv_count):
        pt = rhino3dm.Point4d(u,v,u+v, 1.0)
        ns.Points[(u,v)] = pt

print('Is Surface Valid: ' + str(ns.IsValid))

A thread with a similar request: Help Needed with Creating a NURBS Surface Using rhino3dm.js

3

Thanks for the reply @fraguada

I also achieved some progress on my side but with your code I get the same error when I try to add the nurbs surface to the model:

import rhino3dm

rational = False
dim = 3
u_cv_count = 6
v_cv_count = 6
u_degree = 3
v_degree = 3
u_order = u_degree + 1
v_order = v_degree + 1

ns = rhino3dm.NurbsSurface.Create(dim, rational, u_order, v_order, u_cv_count, v_cv_count)

#generate knots
ns.KnotsU.CreateUniformKnots(1.0)
ns.KnotsV.CreateUniformKnots(1.0)

#create points
for u in range(0, u_cv_count):
    for v in range(0, v_cv_count):
        pt = rhino3dm.Point4d(u,v,u+v, 1.0)
        ns.Points[(u,v)] = pt

if ns.IsValid:
    print('Is Surface Valid: ' + str(ns.IsValid))
    model = rhino3dm.File3dm()
    model.Objects.AddSurface(ns)
    #sc.doc.Views.Redraw()
    model.Write('test.3dm', 0)
else:
    print('Is Surface Valid: ' + str(ns.IsValid))

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image1112×266 15 KB

4

Try

model.Objects.Add(ns, None)
5

The documentation also tells you to give ob attributes with AddSurface: File3dmObjectTable — rhino3dm 8.4.0 documentation

6

Yeah, but what are these attributes supposed to be?
It doesn’t say.

7

an instance of object attributes, but you can try the None if you want to. But the object attributes are: ObjectAttributes — rhino3dm 8.4.0 documentation

8

This worked, thanks.

9

I see, yes, these are good to be entered.
But if you look just at the File3dmObjectTable class you don’t really know what is meant by attributes

10

here’s my final working example:

def TST():
    dimension = 3
    degreeU = 3
    degreeV = 3
    numCtrlPtsU = 4
    numCtrlPtsV = 4
    numKnotsU = 8
    numKnotsV = 8
    isRational = False
    continuity = 2
    KnotVectorU = [0.0, 0.0, 0.0, 0.0, 50.0, 50.0, 50.0, 50.0][1:-1]
    KnotVectorV = [0.0, 0.0, 0.0, 0.0, 50.0, 50.0, 50.0, 50.0][1:-1]
    ControlPtList = [[0.0, 0.0, 0.0],
                     [0.0, 15.0, 0.0],
                     [0.0, 30.0, 0.0],
                     [0.0, 45.0, 0.0],
                     [15.0, 0.0, 0.0],
                     [15.0, 15.0, -30.0],
                     [15.0, 30.0, 0.0],
                     [15.0, 45.0, 0.0],
                     [30.0, 0.0, 0.0],
                     [30.0, 15.0, 0.0],
                     [30.0, 30.0, 30.0],
                     [30.0, 45.0, 0.0],
                     [45.0, 0.0, 0.0],
                     [45.0, 15.0, 0.0],
                     [45.0, 30.0, 0.0],
                     [45.0, 45.0, 0.0]]
    WeightsList = [1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0]
    
    nurbs_surface = rhino3dm.NurbsSurface.Create(dimension, isRational, degreeU + 1, degreeV + 1, numCtrlPtsU, numCtrlPtsV)
    
    # add the knots
    for i in range(0, len(nurbs_surface.KnotsU)):
        nurbs_surface.KnotsU[i] = KnotVectorU[i]
    
    for j in range(0, len(nurbs_surface.KnotsV)):
        nurbs_surface.KnotsV[j] = KnotVectorV[j]

    point4d_list = []
    # add the control points
    for i in range(0, len(ControlPtList)):
        pt4d = [ControlPtList[i][0], ControlPtList[i][1], ControlPtList[i][2], WeightsList[i]]
        #print(pt4d)
        point4d_list.append(rhino3dm.Point4d(pt4d[0], pt4d[1], pt4d[2], pt4d[3]))
        

    i = 0
    for u in range(numCtrlPtsU):
        for v in range(numCtrlPtsV):
            #print((u, v), i)
            nurbs_surface.Points.__setitem__((u, v), point4d_list[i])
            i = i + 1
    
    #
    if nurbs_surface.IsValid:
        print('nurbs_surface.IsValid = True')
        model = rhino3dm.File3dm()
        model.Objects.Add(nurbs_surface, None)
        model.Write('test0.3dm', 0)
    else:
        print('nurbs_surface.IsValid = False')

image
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