help in finding pixel coords of polygon vertices

Hi.

I have an image(1K x 1K, fits format), whose outer boundary is built-up of many hexagons. It has 30 vertices. I would like a way to find the pixel coords of each vertix, non-interactively, since eventually there will be many of these sort of images. All the info I have been able to find about polygons assume one knows these coord already.
Does anyone here know of a way to find the vertices? I have access to IDL, as well as C, under Linux.

Thanks,

Jim

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