   2.5d,2d map with 3d charactor
  I render the map in the ortho mode,and render charators in the perspective mode.nothing strange in ortho mode,but in perspective mode.I place camera at (0,32,32),and look at (0,0,0),viewport is (0,0,800,600),and 2D(400,300) is the 3D point(0,0,z) that project to.when I want to place a charactor at (100,100),I unproject the coordinate (100,100) to the 3d space,then render the charactor.question is how can I make the charactor same size at any coord?because of perspective projection,the charactor is not the same size when it was placed at diffirent screen coordinate.thanks.   
  Move the camera with the character, or don't use perspective. :/ You can, if you really have to, use a different camera (and viewport) for the map and the character, I guess. (The character's viewport is the size of one tile, and is updated to line up with the character's current tile.)   