Resolving 3D Coordinates from 2D Visual Coordinates

Topics: User Forum
Apr 23, 2007 at 2:06 PM
I've created a 2D visual that fires events when child elements are clicked. I'd like to translate a 3D plane mesh onto the center of the control that is clicked, however I can't seem to figure out how to map the 2D point that I get from the event back to the 3D coordinate system.

Thanks in advance.
Oct 25, 2007 at 4:39 PM
Did you ever get this sorted?

Mar 5, 2008 at 12:37 PM
Edited Mar 5, 2008 at 12:38 PM
Hi, I expect this code helps you (and others)

Be aware, host window should be maximized, camera looking straight towards -Z direction, upVector = 0,1,0.

I use this code to convert from Mouse coordinates to 3d World coordinates for Drag&Drop objects in scene, I believe is buggy as is first implementation, so check it and feel free to fix it. :)

PositionX, PositionY, PositionZ represents object world coordinates, (not local coordinates, or offsets in local space)

// How this routine works
// At certain Z relative from Camera Position and certaing FoV (in radians)
// the plane where element lies has certain dimensions (width and height in 3d Space)
// so calculate this width and height in 3d and scale 2D mouse displacement on viewport to this relative coordinates

Point position = e.GetPosition(Scene.Viewport3D); // e is MouseEventArgs

double width = Scene.Viewport3D.ActualWidth;
double height = Scene.Viewport3D.ActualHeight;

double xx, yy;

xx = position.X - width / 2; // centered mouse X
yy = (position.Y - height / 2 ) * -1; // positive Y is up, invert centered mouse Y

double aspectRatio = width / height; // aspectRatio on Screen

double zPlane = this.PositionZ - Scene.ActiveCamera.Position.Z; // object position in 3D Space relative from camera, Z axis fixed.

zPlane = zPlane + zPlane * 0.155; // arbitrary adjustment, why? (I don't know) :) (seems calculations are buggy.

double fov = Math3D.Deg2Rad(Scene.ActiveCamera.FieldOfView); // convert to radians

double Height_3DAtZ = Math.Abs(System.Math.Tan(fov / 2) * zPlane); // Calculate height at z Position

double Width3DAtZ = Height3DAtZ * aspectRatio; // calculate width from height and aspect ratio

// calculate position

double x = xx / (width / 2);

x = (Width_3DAtZ / 2) * x;

//double y = yy / (Height_3DAtZ / 2);

double y = yy / (height / 2);

y = (Height_3DAtZ / 2) * y;

// Set current object current position
this.PositionX = x;
this.PositionY = y;


Mar 6, 2008 at 7:19 PM
Many thanks for this Jesus.

I actually abandoned that part of the project I was working on due to time.

I hope that this code serves as a handy guide to those who follow us here...