How to get a plan picture from ortho pictures?

[Morten Nielsen]

>If you are looking for airphoto orthorectification capabilities, then I
>think you will find it exists in GRASS though I have never tried to
>use this capability.

You still need inner and exterior orientation parameters of the images,
camera parameters and lens distortion measurements. Furthermore you need a
digital elevation model to do a proper orthorectification.

If the images have been used for photogrammetric mapping, the orientation
parameters probably exist already, but then you still need a DEM. Just be
aware that if the images have been oriented using single model setups
instead of using bundle adjustments / aerotriangulation, you will probably
get a poor result. Bottom line is that this is no easy task unless you
already have a full blown orthophoto production setup (which I assume you
don't have).

Best regards
Morten Nielsen