Mouse pan and camera move

I want to change mouse left drag event,by default,keep mouse left down and drag model,the model will rotate centered by earth, i want to drag model like camera move up or move left,such when i keep mouse left down and move up,the camera move up, i tried like this:


but it has a problem,when my camera is far away from the model,the camera moved too short.how to let model follow mouse move?