Thanks AeroShark333, it works.

Let's say the model is rendered on a 1440*1440 screen, and I have a 2d point like (x, y), i want to place the model base on this point, so i try to translate this point to world space point and do translation with the following code,

`SimpleVector targetPosition = new SimpleVector();`

Interact2D.reproject2D3DWS(world.getCamera(), frameBuffer,

x, y, world.getCamera().getPosition().z, targetPosition);

model.getRoot().translate(

targetPosition.x -model.getRoot().getTransformedCenter().x,

targetPosition.y -model.getRoot().getTransformedCenter().y,

0);

but i found that the targetPosition.x will be decrease if x increase, I log the result as follow,

`2d: PointF(518.5, 746.5) => 3d:(14.027778,-1.8055556,-80.0)`

2d: PointF(677.16003, 587.04706) => 3d:(2.9861112,9.236111,-80.0)

So my model will be moved oppositely. Have any idea? Thanks!