Question

I’m writing a WPF application that displays terrain in 3D.

When I perform hit testing, the wrong 3D point is returned (not the point I clicked on).

I tried highlighting the triangle that was hit (by creating a new mesh, taking the coordinates from the RayMeshGeometry3DHitTestResult object). I see that the wrong triangle gets hit (a triangle is highlighted, but it is not under the cursor).

I’m using a perspective camera with field of view of 60, and the near and far planes are of 3 and 35000 respectively.

Any idea why it might happen and what I can do to solve it?

Let me know if you need any more data.

Edit: This is the code I use to perform the hit testing:

private void m_viewport3d_MouseDown(object sender, MouseButtonEventArgs e)
{
    Point mousePos = e.GetPosition(m_viewport3d);
    PointHitTestParameters hitParams = new PointHitTestParameters(mousePos);
    HitTestResult result = VisualTreeHelper.HitTest(m_viewport3d, mousePos);
    RayMeshGeometry3DHitTestResult rayMeshResult = result as RayMeshGeometry3DHitTestResult;
    if (rayMeshResult != null)
    {
        MeshGeometry3D mesh = new MeshGeometry3D();
        mesh.Positions.Add(rayMeshResult.MeshHit.Positions[rayMeshResult.VertexIndex1]);
        mesh.Positions.Add(rayMeshResult.MeshHit.Positions[rayMeshResult.VertexIndex2]);
        mesh.Positions.Add(rayMeshResult.MeshHit.Positions[rayMeshResult.VertexIndex3]);
        mesh.TriangleIndices.Add(0);
        mesh.TriangleIndices.Add(1);
        mesh.TriangleIndices.Add(2);
        GeometryModel3D marker = new GeometryModel3D(mesh, new DiffuseMaterial(Brushes.Blue));
        //...add marker to the scene...
    }
}

Answer 1

Figures out it was a Normalize issue. I shouldn’t have normalized the camera’s look and up vectors. In the scales I’m using, the distortion is too big for the hit test to work correctly.