How to get 3D coordinates from glControl by clicking or selecting with the mouse??

Projects a 3D vector from object space into screen space. Reference page contains links to related code samples.
Parameters
source
The vector to project.
projection
The projection matrix.
view
The view matrix.
world
The world matrix.
 
public Vector3 Project(Vector3 source, Matrix projection, Matrix view, Matrix world)
{
    Matrix matrix = Matrix.Multiply(Matrix.Multiply(world, view), projection);
    Vector3 vector = Vector3.Transform(source, matrix);
    float a = (((source.X * matrix.M14) + (source.Y * matrix.M24)) + (source.Z * matrix.M34)) + matrix.M44;
    if (!WithinEpsilon(a, 1f))
    {
        vector = (Vector3) (vector / a);
    }
    vector.X = (((vector.X + 1f) * 0.5f) * this.Width) + this.X;
    vector.Y = (((-vector.Y + 1f) * 0.5f) * this.Height) + this.Y;
    vector.Z = (vector.Z * (this.MaxDepth - this.MinDepth)) + this.MinDepth;
    return vector;
}
 
 
 
Converts a screen space point into a corresponding point in world space.
Parameters
source
The vector to project.
projection
The projection matrix.
view
The view matrix.
world
The world matrix.
public Vector3 Unproject(Vector3 source, Matrix projection, Matrix view, Matrix world)
{
    Matrix matrix = Matrix.Invert(Matrix.Multiply(Matrix.Multiply(world, view), projection));
    source.X = (((source.X - this.X) / ((float) this.Width)) * 2f) - 1f;
    source.Y = -((((source.Y - this.Y) / ((float) this.Height)) * 2f) - 1f);
    source.Z = (source.Z - this.MinDepth) / (this.MaxDepth - this.MinDepth);
    Vector3 vector = Vector3.Transform(source, matrix);
    float a = (((source.X * matrix.M14) + (source.Y * matrix.M24)) + (source.Z * matrix.M34)) + matrix.M44;
    if (!WithinEpsilon(a, 1f))
    {
        vector = (Vector3) (vector / a);
    }
    return vector;
}
 
private static bool WithinEpsilon(float a, float b)
{
    float num = a - b;
    return ((-1.401298E-45f <= num) && (num <= float.Epsilon));
}
 
 
 
 

private void glControl1_MouseClick(object sender, System.Windows.Forms.MouseEventArgs e)
        {
            if (!loadedTK) return; // Play nice   
 
            int[] viewport = new int[4];
            double[] modelViewMatrix = new double[16];
            double[] projectionMatrix = new double[16];
 
            if (checkBoxSelectPoints.Checked == true)
            {
                int mouseX = e.X;
                int mouseY = e.Y;
 
                //Get Matrix
                OpenTK.Graphics.OpenGL.GL.GetInteger(OpenTK.Graphics.OpenGL.GetPName.Viewport, viewport);
                OpenTK.Graphics.OpenGL.GL.GetDouble(OpenTK.Graphics.OpenGL.GetPName.ModelviewMatrix, modelViewMatrix);
                OpenTK.Graphics.OpenGL.GL.GetDouble(OpenTK.Graphics.OpenGL.GetPName.ProjectionMatrix, projectionMatrix);
 
                //Calculate NearPlane point and FarPlane point. One will get the two end points of a straight line
                //that "almost" intersects the plotted point you "clicked".
                Vector3 win = new Vector3(mouseX, viewport[3] - mouseY, 0);   
                Vector3 worldPositionNear;
                Glu.UnProject(win, modelViewMatrix, projectionMatrix, viewport, out worldPositionNear);
                win.Z = 1.0f;
                Vector3 worldPositionFar;
                Glu.UnProject(win, modelViewMatrix, projectionMatrix, viewport, out worldPositionFar);
 
                //Calculate the lenght of the straigh line (the distance between both points).
                double distanceNF = Math.Sqrt(Math.Pow(worldPositionNear.X - worldPositionFar.X, 2) + 
                                              Math.Pow(worldPositionNear.Y - worldPositionFar.Y, 2)+
                                              Math.Pow(worldPositionNear.Z - worldPositionFar.Z, 2));
                double minDist = distanceNF;
 
 
                 //Calculate which of the plotted points is closest to the line. In other words,
                // look for the point you tried to select. Calculate the distance between the 2 endpoints that passes through
                // each plotted point. The one that is most similar with the straight line will be the selected point.
                int selectedPoint = 0;
                for (int i = 0; i < PointsInfo.Count; i++)
                {
                    double d1 = Math.Sqrt(Math.Pow(worldPositionNear.X - PointsInfo[i].Position.X, 2) +
                                          Math.Pow(worldPositionNear.Y - PointsInfo[i].Position.Y, 2) +
                                          Math.Pow(worldPositionNear.Z - PointsInfo[i].Position.Z, 2));
 
                    double d2 = Math.Sqrt(Math.Pow(PointsInfo[i].Position.X - worldPositionFar.X, 2) +
                                          Math.Pow(PointsInfo[i].Position.Y - worldPositionFar.Y, 2) +
                                          Math.Pow(PointsInfo[i].Position.Z - worldPositionFar.Z, 2));
 
                    if (((d1 + d2) - distanceNF) <= minDist)
                    {
                        minDist = (d1 + d2) - distanceNF;
                        selectedPoint = i;
                    }
                }
 
                //Just select/unselect points if the "click" was really close to a point. Not just by clicking anywhere in the screen
                if (minDist < 0.000065)
                {
                    if (selectedPoints.Contains(selectedPoint))
                        selectedPoints.Remove(selectedPoint);
                    else
                        selectedPoints.Add(selectedPoint);
 
                    glControl1.Invalidate();  //paint again 
                }
            }

  if(selected==true)
		 {
 
 
 
		 gl.glGetIntegerv(GL.GL_VIEWPORT, viewport, 0);
               gl.glGetDoublev(GL.GL_MODELVIEW_MATRIX, mvmatrix, 0);
             gl.glGetDoublev(GL.GL_PROJECTION_MATRIX, projmatrix, 0);
             /* note viewport[3] is height of window in pixels */
             realy = viewport[3] - (int) y ;
         System.out.println("Coordinates at cursor are (" + x + ", " + realy);
 
 
         FloatBuffer fb=ByteBuffer.allocateDirect(4).order(ByteOrder.nativeOrder()).asFloatBuffer();
 
         gl.glReadPixels(y, realy, 1, 1, GL.GL_DEPTH_COMPONENT, GL.GL_FLOAT, fb);
         fb.rewind();
 
 
 
 
         glu.gluUnProject((double)x,(double)realy,0,mvmatrix,0,projmatrix,0,viewport,0,wcoordnear,0);
         System.out.println("World coords at z=0.0 are ( " //
                 + wcoordnear[0] + ", " + wcoordnear[1] + ", " + wcoordnear[2]
                 + ")");
 
         glu.gluUnProject((double) x, (double) realy, 1.0, //
                 mvmatrix, 0,
                 projmatrix, 0,
                 viewport, 0, 
                 wcoordFar, 0);
             System.out.println("World coords at z=1.0 are (" //
                                + wcoordFar[0] + ", " + wcoordFar[1] + ", " + wcoordFar[2]
                                + ")");
 
             double distance=Math.sqrt( kare(wcoordnear[0]-wcoordFar[0])+kare(wcoordnear[1]-wcoordFar[1])+kare(wcoordnear[2]-wcoordFar[2]) );
 
             System.out.println("ilk distance "+distance);
             double mindist=distance;
             int selctedi=9999,selected=9999; // I use a grid to hold points 
             for (int i = 0; i < 9; i++)
             {
 
            	  for (int j = 0; j < 9; j++)
                  {
 
            		double d1=  Math.sqrt( kare(wcoordnear[0]-t[i][j][0])+kare(wcoordnear[1]-t[i][j][1])+kare(wcoordnear[2]-t[i][j][2]) );
 
            		double d2=  Math.sqrt( kare(wcoordFar[0]-t[i][j][0])+kare(wcoordFar[1]-t[i][j][1])+kare(wcoordFar[2]-t[i][j][2]) );
 
            		if (((d1 + d2) - distance) <= mindist)
                    {
            			mindist = (d1 + d2) - distance;
 
                       selectedi=i;
                     selectedj=j;
                    }
 
 
                  }
             }
 
             System.out.println(selectedi+" "+selectedj+" the point you select ");
 
 
 
 
      selected=false;
		 }
 
 
 
//like your codes pow(number,2)
public double kare(double a)
	{
		return a*a;
	}

float scale;
Vector3 rotation;
Vector3 depthTestPoint;
private void glCtrlMain_MouseMove(object sender, MouseEventArgs e)
{
    if (mouseDrag)
    {
        switch (e.Button)
        {
            case MouseButtons.Left:
                // get point on mesh
                glCtrlMain.MakeCurrent();
                depthTestPoint = get2Dto3D(e.X, e.Y);
                depthTestPoint /= scale;
                depthTestPoint = Vector3.TransformVector(depthTestPoint,
                    Matrix4.CreateRotationX(MathHelper.DegreesToRadians(-rotation.X)) *
                    Matrix4.CreateRotationY(MathHelper.DegreesToRadians(-rotation.Y)) *
                    Matrix4.CreateRotationZ(MathHelper.DegreesToRadians(-rotation.Z))
                    );
        }
    }
}

GL.Rotate(rotation.X, Vector3.UnitX);
GL.Rotate(rotation.Y, Vector3.UnitY);
GL.Rotate(rotation.Z, Vector3.UnitZ);
GL.Scale(scale, scale, scale);

private Vector3 get2Dto3D(int x, int y)
{
    int[] viewport = new int[4];
    Matrix4 modelviewMatrix, projectionMatrix;
    GL.GetFloat(GetPName.ModelviewMatrix, out modelviewMatrix);
    GL.GetFloat(GetPName.ProjectionMatrix, out projectionMatrix);
    GL.GetInteger(GetPName.Viewport, viewport);
 
    // get depth of clicked pixel
    float[] t = new float[1];
    GL.ReadPixels(x, camera.viewport.height - y, 1, 1, OpenTK.Graphics.OpenGL.PixelFormat.DepthComponent, PixelType.Float, t);
 
    return UnProject(new Vector3(x, viewport[3] - y, t[0]), modelviewMatrix, projectionMatrix, viewport);
}
 
private Vector3 UnProject(Vector3 screen, Matrix4 view, Matrix4 projection, int[] view_port)
{
    Vector4 pos = new Vector4();
 
    // Map x and y from window coordinates, map to range -1 to 1 
    pos.X = (screen.X - (float)view_port[0]) / (float)view_port[2] * 2.0f - 1.0f;
    pos.Y = (screen.Y - (float)view_port[1]) / (float)view_port[3] * 2.0f - 1.0f;
    pos.Z = screen.Z * 2.0f - 1.0f;
    pos.W = 1.0f;
 
    Vector4 pos2 = Vector4.Transform(pos, Matrix4.Invert(Matrix4.Mult(view, projection)));
    Vector3 pos_out = new Vector3(pos2.X, pos2.Y, pos2.Z);
 
    return pos_out / pos2.W;
}