Python secondary development of Solidworks: reading spline curve data

Table of Contents

1. Sketch segment object

2. VBA code analysis

3. python code implementation

Spline curve is a mathematical term. It is a special parametric curve that is generated by curve fitting from a set of control points. The word spline originated from a temporary auxiliary bracket in ship construction. It was later introduced into computer graphics and became a curve fitting method widely used in computer graphics, numerical control programming, engineering modeling and other fields. Depending on the number and type of control points used, spline curves can be divided into third-order spline curves, second-order spline curves, and interpolation spline curves. This example implements Python to read the spline curve of the sketch in the Solidworks part document.

1. Sketch segment object

In Solidworks, the Sketch Segment object represents each part of the sketch, such as lines, arcs, splines, text, etc. These are all subdivisions of sketch segments. For example, a rectangular sketch can be composed of multiple sketch segments, each line segment being an instance of the sketch segment.

Sketch segment objects have specific names inside Solidworks, such as Line8. These names can be used to select and manipulate sketch segments. The SelectByID2 method allows you to select a specific sketch segment using its name.

2. VBA code analysis

Find the following code in the API help and run it through:

'--------------------------------------------- -------
' Preconditions:
' 1. Verify that the specified part template exists.
' 2. Open the Immediate window.
'
' Postconditions:
' 1. Creates a sketch containing two splines.
' 2. Gets each spline's dimension, order, periodicity,
' control point, and knot point data.
' 3. Examine the Immediate window.
'------------------------------------------------ -----
Option Explicit
Dim swApp As SldWorks.SldWorks
Dim swModel As SldWorks.ModelDoc2
Dim swSelMgr As SldWorks.SelectionMgr
Dim swSketchSegment As SldWorks.SketchSegment
Dim swFeature As SldWorks.Feature
Dim swSketch As SldWorks.Sketch
Dim swSplineParamData As SldWorks.SplineParamData
Dim swSketchMgr As SldWorks.SketchManager
Dim points(11) As Double
Dim pointArray As Variant
Dim varCtrlPoints As Variant
Dim varKnotPoints As Variant
Dim status As Boolean
Dim i As Integer
Dim j As Integer
Dim k As Integer
Dim splineCount As Long
Dim splinePointCount As Long
Sub main()
    Set swApp = Application.SldWorks
    Set swModel = swApp.NewDocument("C:\ProgramData\SolidWorks\SOLIDWORKS 2018\templates\gb_part.prtdot", 0, 0, 0)
    'Create a sketch with two splines
    'First spline
    points(0) = -0.185955019567672
    points(1) = 4.16208582005027E-02
    points(2) = 0
    points(3) = -8.62492383138544E-02
    points(4) = 4.03922105323034E-02
    points(5) = 0
    points(6) = -6.72740896322921E-02
    points(7) = 5.40598971292923E-02
    points(8) = 0
    points(9) = -1.41436733240425E-02
    points(10) = -5.70437188125084E-03
    points(11) = 0
    pointArray = points
    Set swSketchMgr = swModel.SketchManager
    Set swSketchSegment = swSketchMgr.CreateSpline((pointArray))
    swModel.ClearSelection2 True
    'Second spline
    points(0) = -8.38342193907238E-02
    points(1) = -3.80341664350112E-02
    points(2) = 0
    points(3) = -6.55490761158148E-02
    points(4) = -1.79490921124739E-02
    points(5) = 0
    points(6) = -1.79387030603664E-02
    points(7) = -6.81344637902441E-02
    points(8) = 0
    points(9) = 6.34819349185705E-02
    points(10) = -3.29692207162395E-02
    points(11) = 0
    pointArray = points
    Set swSketchSegment = swSketchMgr.CreateSpline((pointArray))
    swModel.ClearSelection2 True
    'Sketch
    swSketchMgr.InsertSketch (True)
    'Get each spline's dimension, order, periodicity, control point, and knot data
    status = swModel.Extension.SelectByID2("Sketch 1", "SKETCH", 0, 0, 0, False, 0, Nothing, 0)
    Set swSelMgr = swModel.SelectionManager
    Set swFeature = swSelMgr.GetSelectedObject6(1, -1)
    Set swSketch = swFeature.GetSpecificFeature2
    Debug.Print swFeature.Name
    Debug.Print ""
    splineCount = swSketch.GetSplineCount(splinePointCount)
    For i = 1 To splineCount
        Debug.Print "Spline " & amp; i & amp; ": "
        Set swSplineParamData = swSketch.GetSplineParams5(True, i - 1)
        Debug.Print " Dimension: " & swSplineParamData.Dimension
        Debug.Print " Order: " & swSplineParamData.Order
        Debug.Print " Periodicity: " & swSplineParamData.Periodic
        Debug.Print " Number of control points: " & swSplineParamData.ControlPointsCount
        status = swSplineParamData.GetControlPoints(varCtrlPoints)
        Debug.Print "Control points:"
        For j = 0 To UBound(varCtrlPoints)
            Debug.Print " " & varCtrlPoints(j)
        Next j
        Debug.Print " Number of knots: " & swSplineParamData.KnotPointsCount
        status = swSplineParamData.GetKnotPoints(varKnotPoints)
        Debug.Print " Knot points:"
        For k = 0 To UBound(varKnotPoints)
            Debug.Print " " & varKnotPoints(k)
        Next k
    Next i
End Sub

Sketch 1

Spline 1:
Dimension: 3
Order: 4
Periodicity: 0
Number of control points: 6
Control points:
-0.185955019567672
4.16208582005027E-02
0
-0.150380934953332
3.10398728957725E-02
0
-0.10646390756121
1.79774026593307E-02
0
-5.16578490138504E-02
7.31450269896099E-02
0
-3.05079969277205E-02
2.86910814467778E-02
0
-1.41436733240425E-02
-5.70437188125084E-03
0
Number of knots: 10
Knot points:
0
0
0
0
0.491042198542287
0.606202911975324
1
1
1
1
Spline 2:
Dimension: 3
Order: 4
Periodicity: 0
Number of control points: 6
Control points:
-8.38342193907238E-02
-3.80341664350112E-02
0
-0.077690281088829
-2.89692122866611E-02
0
-5.58988151965229E-02
3.18258179599927E-03
0
-1.75895532053729E-02
-0.10684766264249
0
3.43192698312501E-02
-5.95444361085419E-02
0
6.34819349185705E-02
-3.29692207162395E-02
0
Number of knots: 10
Knot points:
0
0
0
0
0.146797917671912
0.520666331402203
1
1
1
1
Sketch 1

Note: The code provided in the help document is likely to have problems, which mainly appear in the following two places:

The template path opened by swApp.NewDocument must be correct

swModel.Extension.SelectByID2 to correctly select sketch 1

3. python code implementation

import win32com.client as win32
import pythoncom
import numpy as np
def vtPoint(x, y, z):
    #Convert coordinate points to floating point numbers
    return win32.VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_R8, (x, y, z))
def vtObj(obj):
    #Convert to object array
    return win32.VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_DISPATCH, obj)
def vtFloat(list):
    #Convert list to floating point number
    return win32.VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_R8, list)
def vtInt(list):
    #Convert list to integer
    return win32.VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_I2, list)
def vtVariant(list):
    #Convert list to variant
    return win32.VARIANT(pythoncom.VT_ARRAY | pythoncom.VT_VARIANT, list)
swApp = win32.Dispatch('sldworks.application')
swApp.Visible = True
Nothing = win32.VARIANT(pythoncom.VT_DISPATCH, None)
swModel = swApp.NewDocument(r"C:\ProgramData\SolidWorks\SOLIDWORKS 2018\templates\gb_part.prtdot", 0,0,0)
#Create a sketch with two splines
#First spline
points1=(-0.185955019567672,4.16208582005027E-02,0,-8.62492383138544E-02,4.03922105323034E-02,0,
        -6.72740896322921E-02,5.40598971292923E-02,0,-1.41436733240425E-02,-5.70437188125084E-03,0)
pointArray = vtFloat(points1)
swSketchMgr = swModel.SketchManager
swSketchMgr.CreateSpline2(pointArray,1)
swModel.ClearSelection2(True)
#Second spline
points2=(-8.38342193907238E-02,-3.80341664350112E-02,0,-6.55490761158148E-02,-1.79490921124739E-02,0,
         -1.79387030603664E-02,-6.81344637902441E-02,0,6.34819349185705E-02,-3.29692207162395E-02,0)
pointArray = vtFloat(points2)
swSketchMgr.CreateSpline2(pointArray,1)
swModel.ClearSelection2(True)
#Sketch
swSketchMgr.InsertSketch(True)
#Get each spline's dimension, order, periodicity, control point, and knot data
status = swModel.Extension.SelectByID2("Sketch 1", "SKETCH", 0, 0, 0, False, 0, Nothing, 0)
swSelMgr = swModel.SelectionManager
swFeature = swSelMgr.GetSelectedObject6(1, -1)
swSketch = swFeature.GetSpecificFeature2
print(swFeature.Name)
splinePointCount=win32.VARIANT(pythoncom.VT_BYREF|pythoncom.VT_I4, -1)
splineCount = swSketch.GetSplineCount(splinePointCount)
for i in range(1,splineCount + 1):
    print("Spline ",splineCount,i)
    swSplineParamData = swSketch.GetSplineParams5(True, i - 1)
    print(" Dimension: ",swSplineParamData.Dimension)
    print(" Order: ",swSplineParamData.Order)
    print("Periodicity: ",swSplineParamData.Periodic)
    print("Number of control points: ",swSplineParamData.ControlPointsCount)
    varCtrlPoints = win32.VARIANT(pythoncom.VT_BYREF | pythoncom.VT_VARIANT, -1)
    status = swSplineParamData.GetControlPoints(varCtrlPoints)
    CtrlPoints=np.array(varCtrlPoints.value).reshape(-1,3)
    print("Control points:")
    for j in range(len(CtrlPoints)):
        print(CtrlPoints[0])
    print("Number of knots: ",swSplineParamData.KnotPointsCount)
    varKnotPoints=win32.VARIANT(pythoncom.VT_BYREF|pythoncom.VT_VARIANT, -1)
    status = swSplineParamData.GetKnotPoints(varKnotPoints)
    KnotPoints = np.array(varKnotPoints.value).reshape(-1, 1)
    for j in range(len(KnotPoints)):
        print(KnotPoints[j])

Sketch 1
Spline 2 1
Dimension: 3
Order: 4
Periodicity: 0
Number of control points: 6
Control points:
[-0.18595502 0.04162086 0. ]
[-0.18595502 0.04162086 0. ]
[-0.18595502 0.04162086 0. ]
[-0.18595502 0.04162086 0. ]
[-0.18595502 0.04162086 0. ]
[-0.18595502 0.04162086 0. ]
Number of knots: 10
[0.]
[0.]
[0.]
[0.]
[0.4910422]
[0.60620291]
[1.]
[1.]
[1.]
[1.]
Spline 2 2
Dimension: 3
Order: 4
Periodicity: 0
Number of control points: 6
Control points:
[-0.08383422 -0.03803417 0. ]
[-0.08383422 -0.03803417 0. ]
[-0.08383422 -0.03803417 0. ]
[-0.08383422 -0.03803417 0. ]
[-0.08383422 -0.03803417 0. ]
[-0.08383422 -0.03803417 0. ]
Number of knots: 10
[0.]
[0.]
[0.]
[0.]
[0.14679792]
[0.52066633]
[1.]
[1.]
[1.]
[1.]

The difficulty with this part is:

Spline data type mismatch

status = swSplineParamData.GetControlPoints(varCtrlPoints) data type mismatch

status = swSplineParamData.GetKnotPoints(varKnotPoints) data type mismatch

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