CODEWITHSUNDEEP
c#wpfmatrix
Nic
Nic

Reputation: 1310

Matrix3D for a positive rotation around z in WPF

Let P be a Point3D such that P = {1,0,0} . I need to define a rotation around the Z axis of +45deg and apply it to P. Under a right-hand convention, the transformation M is defined:

M =

0.707 -0.707 0 0    
0.707 0.707 0 0     
0 0 1 0             
0 0 0 1

Mathematically:

M x P = 

0.707 -0.707 0 0         1           0.707
0.707 0.707 0 0     X    0       =   0.707
0 0 1 0                  0           0
0 0 0 1                  1           1

here is my C# code: 

    private void testMatrix3D() {
        double angle_rad = Math.PI/4;
        double cos = Math.Cos(angle_rad);
        double sin = Math.Sin(angle_rad);
        Matrix3D mat = new Matrix3D(cos, -sin, 0, 0, sin, cos, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);

        Point3D p = new Point3D(1, 0, 0);

        Point3D transformedP = mat.Transform(p);


        Debug.WriteLine("p = " + p);
        Debug.WriteLine("mat = " + mat);
        Debug.WriteLine("transformedP = " + transformedP);

    }

Unfortunately, the result is transformedP = {0.707, -0.707, 0} and NOT transformedP= {0.707, 0.707, 0}

What am I doing wrong?

Upvotes: 0

Views: 622

Answers (1)

JeffRSon
JeffRSon

Reputation: 11196

Since WPF stores vectors in matrices row-wise you need to exchange those:

Matrix3D mat = new Matrix3D(cos, sin, 0, 0, -sin, cos, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1);

Upvotes: 1

Related Questions