[aprssig] Aerial or Satellite Photos/Map for APRS Use
scott at opentrac.org
Sun Dec 16 14:04:31 CST 2007
> Does anyone know of a source of RECENT Aerial/Satellite photos that could be
> used as a map ? I believe that Xastir has a way to convert photos to a map
> if you can calibrate the photo to known points.
Check what's available through Google Earth / Google Maps, Microsoft's
mapping system, and the USGS. In my experience, if you want imagery
from a particular point in time, unless you get really lucky you just
have to pay for it.
You could try geoeye.com (formerly Space Imaging, I think) - last time I
looked at IKONOS imagery, I think it was a few hundred bucks to get
something from their archives, and in the thousands to acquire new
images - or at least to get a few attempts to acquire images.
Hmm.. I just found one site that claims it's about $20 per square km at
1m resolution, color. I'm not sure if that's orthorectified or not, and
I don't know what the minimum purchase is.
> impact. If anyone has any leads I would appreicate it. My last choice is to
> set out markers on all four corners I guess then hire a local crop duster to
> take me up with a camera, I can then apply the lat/long to the 4 markers and
> hopefully import it into Xaster or UIView32.
I know little about aerial photography, but I think that for mapping
purposes, if you want it to be reasonably accurate you need to be able
to correct for the angle of the picture, effects of terrain, lens
geometry, and so forth. Maybe if you could get reasonably high,
directly over the property, and get a good picture with a long lens it
wouldn't be as distorted.
I got back about 500 downward-facing images from my balloon flight last
year and I worked on overlaying them on Google Earth. It worked well
enough to see where they were taken, but there was no way to make most
of them line up well - there was too much tilt and perspective
distortion, and no way to correct for it with the tools provided.
For some reading on the subject, look up 'photogrammetry' and
'orthorectification'. Wikipedia has articles on both.
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