ARtoolkit and openGL


In artoolkit, i want to draw on some pixels which lies on the marker area.
and i can get its coordinates (x,y in screen coordinate) using marker_info2 and dataptr.

my problem is when i use GL_POINTS to draw on these pixels, it becomes fixed on its x,y position.
So, now I’m trying to use gluUnProject to get the relative position of these pixels to the marker
but it seems like separated dots, how can i fix it?any suggestions?