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[aprssig] Aerial or Satellite Photos/Map for APRS Use

Rich Garcia k4gpsc at gmail.com
Sun Dec 16 20:36:22 UTC 2007


Been down that road, Google Earth is about 1 year back, maybe a bit more.
Searched other's that "claim" to have the latest and greatest with no luck.
It's a good photo but a bit old, great to try to blow up and make into an
11x14 but I have not figured out exactly how to do that yet and keep a good
resolution, but not something I want for APRS.

In March we had a logging company come in and clear 4 acres plus thin out
40% of the rest of the land. A photo of that is my primary objective since I
want to see the trails and the impact from the logging. Finally the home was
finished up in October and that is the final photo I would like but also to
import it into some flavor of APRS for day to day use.

I guess eventually the images will show up in public domain but that may be
2-7 years down the road. I really should have hired that crop duster back in
March/May to take a few pictures, I may not ever get a pic of the land
cleared without the house but eventually I'll get one with the house on
Terra or such.
Rich

-----Original Message-----
From: Scott Miller [mailto:scott at n1vg.net]
Sent: Sunday, December 16, 2007 2:44 PM
To: k4gps at arrl.net; TAPR APRS Mailing List
Subject: Re: [aprssig] Aerial or Satellite Photos/Map for APRS Use


> 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.

Scott
N1VG





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