[GRASS5] Re: GDAL, GRASS and AVHRR

[Helena Mitasova]

> > Ahh. We experienced this problem at PCI with some kinds of AVHRR data as
> > well.  I believe our solution there was to add a "thin plate splines"
> > transformation modelling in addition to the existing polynomial
> > transformations.  This is a transform with as many terms as there are
> > GCPs and gives increasing weight to gcps that are closer to the point
> > being warped.  Almost a piecewise warp.>
> > Implementing thin-plate splines, or some similar transformation
> > mechanism is not trivial.  It also doesn't specifically belong in
> > GDAL.>
> > I would suggest that this issue be brought back to the GRASS dev list,
> > and see if any of us can find a suitable source for a thin plate spline
> > algorithm (or another with similar properties).  This could then
> > be implemented in i.rectify or perhaps an i.rectify.tps.
>
> So: Is there anyone willing to help with extending i.rectify to
> support also splines based rectification? Could we probably use functions
> from src/libes/rst_gmsl/

I agree that it should be implemented in i.rectify.
You sure can take advantage of  rst_gmsl. There should be a paper by Fogl(?)
from
GISEM3 conference in Santa Fe 1996 where he presented the rectification with
a number of functions including RST (it was TPS then so many people
refer to it thin plate spline) and RST performed really well. I will be happy
to help,
but you need to tell me where that interpolation/approximation needs to be
applied as I am not familiar with i.rectify.

Helena.

P.S. Fogl then implemented RST for ERDAS - he did an incredibly thorough
testing and discovered
a bug where I typed in 5555... instead of 6666... in one of the constants - it
was there
for years and never caused visible problems, but neverthless it was a bug
.055555555555556e+00, -.010416666666667e+00, /*fixed bug 415.. repl. by 416..*/



>
> ?
>
> AVHRR is a pretty interesting and huge data base as this set of satellites
> was initially launched 1982. Data are available here (download):
> Satellite Active Archive (SAA)
> http://www.saa.noaa.gov/
>
> Thanks in advance,
>
>  Markus
>
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