Unexpected output of Transform3D.Transform method in WPF

Question

I need to define a 3D transformation and apply it to a point p ={1000, 0, 0}.

For example, say one needs to apply a Pi/2 rotation around the z axis. I defined the transformation using a MatrixTransform3D. From the code below:

EXPECTED OUTPUT: trPoint = {0, 1000, 0}

ACTUAL OUTPUT: trPoint = {0, -1000, 0}.

QUESTION : Perhaps the Transform3D.Transform method applies the inverse transform instead?

    private void testTransformationMat() {
        Point3D p = new Point3D(1000, 0, 0);

        double angle = System.Math.PI / 2;

        double cos = System.Math.Cos(angle);
        double sin = System.Math.Sin(angle);

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

        Transform3D tr = new MatrixTransform3D(mat_z);

        Point3D trPoint = tr.Transform(p);

        Debug.WriteLine(trPoint);

    }

EDIT: To get things straight, as far as I've always known, a homogeneous transformation is applied multiplying a 4x4 matrix with a 4x1 vector. For a +45deg rotation around the z axis, under right-hand convention, we obtain:

0.707 -0.707 0 0         1000        707
0.707 0.707 0 0     X    0       =   707
0 0 1 0                  0           0
0 0 0 1                  1           0

If we invert the matrix, the multiplication returns a negative y component which is not coherent with a +45deg rotation around Z.

0.707 0.707 0 0         1000        707
-0.707 0.707 0 0     X    0       =  -707
0 0 1 0                  0           0
0 0 0 1                  1           0

Answer 1

From 3-D Transformations Overview

Note:Windows Presentation Foundation (WPF) 3-D is a right-handed system, which means that a positive angle value for a rotation results in a counter-clockwise rotation about the axis.