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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | RE: GISList: orthorectify |
| Date: |
08/28/2002 08:14:32 PM |
| From: |
Dimitri Rotow |
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> Can Manifold currently orthorectify imagery or is that something under
> development?
>
> In the Manifold help it states: "This process is often called
> orthorectification or (in some contexts) georegistration" but I think that
> over simplifies the meaning or orthorectification.
> Orthorectification tends
> to refer to (or even focus on) the removal of terrain effects during the
> georegistration process. Correct me if I'm wrong but my understanding is
> that the image transformation tools in Manifold are not well suited to
> removing terrain distortions. Using traditional rubber sheeting methods to
> correct aerial photos would be a very difficult task/impossible
> in hilly or
> mountainous terrain.
>
Absolutely correct. To do true orthorectification you must not only deal
with terrain distortions but also optical distortions induced by the camera
system. Manifold won't do that, nor is it under development. However,
some people wrongly use the phrase "orthorectify" as a synonym for
garden-variety, rubber sheeting georegistration. I think the phrase in the
Help file was intended to guide those people to the right topic and nothing
more.
By the way, as a poor man's "orthorectification" the georegistration tools
work surprisingly well in reasonably flat terrain (as is the terrain in many
cases where cities, developments, etc, are located). I've heard of cases
where people went up for a $100 flight in a small Cessna from the local
airport and shot off a roll of film in an ordinary camera, scanned in the
pictures, georegistered them and were able to use the resultant images for
all sorts of things: vectorization for AM/FM, planning, making presentations
of proposed developments, etc.
Cheers,
Dimitri
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