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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | [gislist] ortho |
| Date: |
05/19/2004 09:35:01 AM |
| From: |
Chip Westbrook |
|
|
>
> There is something wrong with this picture you say your photography =
was
> flown at 1:400 if this is so your plane was only 400 feet off the =
ground.
> You cant have a orthophoto that is sharp on one side and out of focus =
on
the
> other unless you are photographing a wall. It sounds like your photoes
have
> been rubber sheeted to gather.
>
>
> chip
>
> > ---------- Forwarded Message -----------
> > From: Jayachandran Mani <jayachandran_m@yahoo.com>
> > To: rlake@galdosinc.com, Eric Sandoval <sandoval_ej@yahoo.com>
> > Sent: Mon, 10 May 2004 06:02:10 -0700 (PDT)
> > Subject: Re: [gislist] Orthoimagery
> >
> > hi
> > aerial photography @ 1 : 400 scale is quite a good
> > resolution. It is amazing to have the photography done
> > at this scale.
> > Colour balancing between two different flightlines is
> > a major task in photogrammetry.
> > The fuzzy appearance may be due to the dodging
> > parameters used during the mosaicing process or it may
> > be due to the improper positional accuracy of the
> > features between the orthos from different flightlines
> > / models in the same flight line.
> >
> > It is always suggested to have the ortho created for
> > the center of the photograph to avoid the relief
> > errors (as the scale of photography is large) and to
> > avoid the distortion errors at the peripherals. i.e
> > instead of creating ortho photos for one model
> > completely (with one/two underlying images of the
> > model), the ortho should be created for the central of
> > the photograph. For this DEM may have to merged for
> > the adjacent models. Initial planning of this may sort
> > this issue. This way may solve the positional
> > inaccuracies.
> >
> > For colour balancing, orthovista will be good.
> > Recently we had an experience of creating a seamless
> > ortho mosaic in LPS (leica photogrammetry suite),
> > which was excellent. but it was a b&W imagery. For
> > colour, atleast within the mosaic, we can be able to
> > get a seamless mosaic, with more extra care
> > (considerable time). Photoshop may also have to be
> > used extensively sometimes.
> >
> > regards
> > Jay
> >
> > --- Ron Lake <rlake@galdosinc.com> wrote:
> > > Eric Sandoval wrote:
> > >
> > > >Hello Listers:
> > > >
> > > >I have a question for the orthoimagery experts out
> > > there. We have imagery that exhibits substantial
> > > radiometric inconsistencies. Our imagery was flown
> > > at 1:400 scale or 6 inch resolution. The various
> > > flight lines were merged and then were processed to
> > > choose the best image based on sun angle,
> > > clarity,etc. The images were then color balanced.
> > > >
> > > >Our problem: Along the seems of our imagery a
> > > distinct difference can be seen. On one side of the
> > > seem the ground features will appear clear and on
> > > the other side they appear fuzzy. We were told by
> > > the survey company that these differences were the
> > > result of different flight lines. The difference in
> > > contrast, clarity and sharpness are a function of
> > > flight lines were taken at different times of the
> > > day and the position of the features. Some features
> > > are on the outer portion of the flight line and
> > > therefore exhibit lean due to camera angle. Flight
> > > lines were planned with a standard 60/30 overlap.
> > > >
> > > >My question: Can't these problems be resolved
> > > through processing or surveying additional flight
> > > lines? I understand it's unreasonable to acquire
> > > additional flight lines after the initial survey
> > > (cost prohibitive), but couldn't additional flight
> > > lines been planned if these problems were known in
> > > advance (which they were)? Does this type of
> > > problem occur in all orthoimagery?
> > > >
> > > >Any insight or comments that you can provide would
> > > be most appreciated.
> > > >
> > > >Thank you,
> > > >
> > > >-Eric Sandoval
> > > >
> > > >
> > > >
> > > >---------------------------------
> > > >Do you Yahoo!?
> > > >Win a $20,000 Career Makeover at Yahoo! HotJobs
> > > >_______________________________________________
> > > >gislist mailing
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