Complex Geometry in Architecture

‘Linestring Bezier Approximation after Casteljau’s algorithm
‘Sebastian Gmelin
’24.10.2009

‘draw and select linestring and run script

Const cDiv As Long = 5 ‘subdivision at which guidlines are drawn and a copy of the drawing set is created
Const div As Long = 50 ‘subdivision between cDiv for bezier spline points (total subdivision = cDiv * div)

Dim cPoints() As Point3d
Dim bPoints() As Point3d
Dim cSize As Point3d
Dim cLine As Element
Private Sub ScanDesignFile()
‘scan active designfile for selected linestrings
    Dim oElEnum As ElementEnumerator
    Dim oElem As Element

    ‘get collection of selected elements
    Set oElEnum = ActiveModelReference.GetSelectedElements
    ActiveModelReference.UnselectAllElements
   
    ‘go through selection set
    While oElEnum.MoveNext
        Set oElem = oElEnum.Current
        ‘check if active element is linestring
        If (oElem.IsVertexList) Then
            Debug.Print (“Linestring”)
            cPoints = oElem.AsVertexList.GetVertices ‘save collection of vertices
            Set cLine = oElem
        End If
    Wend
End Sub

Private Sub getSize()
‘get linestring size for element copies offset

Dim i As Long
Dim min As Point3d
Dim max As Point3d
Dim lineString As Element

    min = Point3dFromXYZ(1E+17, 1E+17, 1E+17)
    max = Point3dFromXYZ(-1E+17, -1E+17, -1E+17)
   
    For i = 0 To UBound(cPoints)
        If cPoints(i).X > max.X Then max.X = cPoints(i).X
        If cPoints(i).Y > max.Y Then max.Y = cPoints(i).Y
        If cPoints(i).Z > max.Z Then max.Z = cPoints(i).Z
        If cPoints(i).X < min.X Then min.X = cPoints(i).X
        If cPoints(i).Y < min.Y Then min.Y = cPoints(i).Y
        If cPoints(i).Z < min.Z Then min.Z = cPoints(i).Z
    Next
   
    cSize = Point3dFromXYZ(0, max.Y – min.Y, 0)
    cSize.Y = cSize.Y * -1.2
   
End Sub

Sub Casteljau()

Dim i As Long
Dim k As Double
Dim p As Long
Dim points() As Point3d ‘last parent point collection
Dim dPoints() As Point3d ‘division points
Dim mPoints() As Point3d ‘points to draw
Dim lineString As Element
Dim color As Long
Dim count As Long
Dim moveCount As Long

ReDim bPoints(0)
bPoints(0) = cPoints(0)
count = 0
moveCount = 0

For k = 1 / (div * cDiv) To 1 Step 1 / (div * cDiv) ‘k is scale factor of divisions
    points = cPoints
    dPoints = cPoints
    color = 48
    ‘calculate divisions
    While UBound(dPoints) > 1
    ‘points is the collection of vertices of the parent linestring
    ‘dPoints is the child linestring at scalefactor k
        For i = 0 To UBound(points) – 1
            dPoints(i) = Point3dAdd(Point3dScale(Point3dSubtract(points(i + 1), points(i)), k), points(i))
        Next i
        ReDim Preserve dPoints(UBound(points) – 1)
        ‘draw guidlines
        If count = div Then
            mPoints = dPoints
            ‘calculate offset
            For p = 0 To UBound(mPoints)
                mPoints(p) = Point3dAdd(mPoints(p), Point3dScale(cSize, moveCount))
            Next
            ‘draw line
            Set lineString = CreateLineElement1(Nothing, mPoints)
            lineString.color = color
            lineString.LineStyle = ActiveDesignFile.LineStyles(3)
            ActiveModelReference.AddElement lineString
            lineString.Redraw
            color = color + 48
        End If
        points = dPoints
    Wend
    count = count + 1
    ‘draw progress of bezier curve
    If count > div Then
        count = 0
        ‘copy control polygon
        Set lineString = ActiveModelReference.CopyElement(cLine)
        Call lineString.Move(Point3dScale(cSize, moveCount))
        ActiveModelReference.AddElement lineString
        lineString.Redraw
        moveCount = moveCount + 1
        ‘calculate offset of beziers pline
        mPoints = bPoints
        For p = 0 To UBound(mPoints)
            mPoints(p) = Point3dAdd(mPoints(p), Point3dScale(cSize, moveCount – 1))
        Next
        ‘draw bezier progress
        Set lineString = CreateLineElement1(Nothing, mPoints)
        lineString.color = 3
        lineString.LineWeight = 2
        ActiveModelReference.AddElement lineString
        lineString.Redraw
    End If
    ‘add calculated division point to collection of bezier points
    ReDim Preserve bPoints(UBound(bPoints) + 1)
    bPoints(UBound(bPoints)) = Point3dAdd(Point3dScale(Point3dSubtract(points(1), points(0)), k), points(0))
Next k

‘draw final bezier curve
mPoints = bPoints
For p = 0 To UBound(mPoints)
    mPoints(p) = Point3dAdd(mPoints(p), Point3dScale(cSize, moveCount – 1))
Next
Set lineString = CreateLineElement1(Nothing, mPoints)
lineString.color = 3
lineString.LineWeight = 2
ActiveModelReference.AddElement lineString
lineString.Redraw

End Sub
Sub Main()

    If ActiveModelReference.AnyElementsSelected Then
        ScanDesignFile
        getSize
        Casteljau
    End If

End Sub