[GRASS-user] rectifying digital images

[sebastian sauer]

Hi,

Sat 05 Jan 2008 16:45, Vincent BAIN wrote:
> If you follow Markus' how-to, you may be interested in technical info
> concerning your camera :
> 
> Kodak DCS Pro SLR/n/c
> imager size : 36.0mm x 24.0mm
> pixel size : 7.9µm x 7.9µm

exactly. even if you (for unknown reasons) do not follow Markus' how-to,
you will need this information. and it won't hurt double-checking the
correctness of this data against, the DPI in the EXIF data.

given that, it's pretty straight-forward to set-up precise fiducial
marks.

(cf. http://edclxs22.cr.usgs.gov/osl/figure2.gif && 
http://grass.itc.it/grass63/manuals/html63_user/photo.camera.html )

*but* what is tricky is getting the calibrated focal length right.
(and this of course (distortions!) is a quite important parameter)

> Le samedi 05 janvier 2008 à 23:25 +0800, Maning Sambale a écrit :
> > Camera:  Kodak Pro DCS 14N digital SLR camera 
> > using a 19-35mm Tamron zoom lens set at 19mm focal length
ok, his info is not so shabby, at least you know the "calibrated focal
length" should be ~19mm.

also the spec of the lens should include the focal length tolerance.
(aka by how many percent the calibrated focal length is off from the
value of 19mm.)

cf. http://grass.itc.it/grass63/manuals/html63_user/photo.camera.html &&
and thread "[CREATE] Lens correction database" @ 
http://lists.freedesktop.org/archives/create/2007-May/thread.html#743

> > SHUTTER	FOCAL LENGTH
?? not quite sure. are these actually to different paramenters, namely
the shutter speed && the focal lenght? or what is this??

cheers,
s.

ps: if anyone knows a good trick to do a precise focal length
calibration, plz don't keep it as your secret, but share it with us :))
SCNR.