>From 3d space to screen coordinates you can use camera.screen(), which returns a screen vertex for the position of a 3d object.
>From screen to 3d space its a bit more complicated since you can have infinite solutions. Any ray that reaches the camera at your 2d coordinates is a candidate line for you to place the 3d projection, practically anywhere. However a good solution is to define a virtual (mathematical) plane in space, always looking at the camera, and cast a ray from the cameras perspective onto the plane and use this ray's intersection with the plane as your produced 3d point. You can see this implemented in Rob's Sierpisnki demo: http://www.infiniteturtles.co.uk/blog/away3d-merry-christmas-2008 Near the start of the onEnterframe() he uses: persp = camera.zoom/(1 + 1600/camera.focus); mouseVector.x = view.mouseX/persp; mouseVector.y = view.mouseY/persp; mouseVector.z = 1600; where 1600 is how far the virtual plane is positioned from the camera. Of course this latter topic is more subjective than the first, and you could device many other ways to obtain a 3d coord from a screen coord.
