Polygon rotation around center

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hi I have an array of points that makes a polygon. how can i rotate polygon around its center.

What I have tried:

Public Function RotatePoints(_Points() As Point, _CenterPoint As Point, _Degree As Double) As Point()
    Dim Output() As Point = _Points.Clone()

    Dim Angle As Double = (_Degree / 180.0) * Math.PI
    For Index As Integer = 0 To Output.Length - 1
        Output(Index) = New Point((Math.Cos(Angle) * (Output(Index).X - _CenterPoint.X)) + _CenterPoint.X, (Math.Sin(Angle) * (Output(Index).Y - _CenterPoint.Y)) + _CenterPoint.Y)
    Next

    Return Output
End Function

Posted 17-Jan-18 22:40pm

mashali

Updated 18-Jan-18 0:35am

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Kornfeld Eliyahu Peter 18-Jan-18 5:50am

point-by-point?

mashali 18-Jan-18 6:45am

thanks. problem solved, my algorithm was wrong.

2 solutions

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OriginalGriff · Accepted Answer · 2018-01-18T00:13:00

Solution 1

Simple: your algorithm is wrong.
See here: Geometric Operations - Rotate[^]

I would suggest that you "break out" each coordinate into a separate set of lines, get X working - obviously, use the debugger to check - and then repeat for Y. When both work, amalgamate the separate stages of X and Y into single lines and create your new point.

Posted 18-Jan-18 0:13am

OriginalGriff

Comments

mashali 18-Jan-18 6:32am

Thanks OriginalGriff
its work :)

OriginalGriff 18-Jan-18 6:39am

You're welcome!

mashali · Accepted Answer · 2018-01-18T00:35:00

Special thanks to OriginalGriff

Public Function RotatePoints2(_Points() As Point, _CenterPoint As Point, _Degree As Double) As Point()
    Dim Output() As Point = _Points.Clone()

    Dim Angle As Double = (_Degree / 180.0) * Math.PI
    For Index As Integer = 0 To Output.Length - 1
        Dim Dx As Integer = (Output(Index).X - _CenterPoint.X)
        Dim Dy As Integer = (Output(Index).Y - _CenterPoint.Y)
        Output(Index).X = (Math.Cos(Angle) * Dx) - (Math.Sin(Angle) * Dy) + _CenterPoint.X
        Output(Index).Y = (Math.Sin(Angle) * Dx) + (Math.Cos(Angle) * Dy) + _CenterPoint.Y
    Next

    Return Output
End Function