[GRASS5] Re: making a "true-color" landsat composite

Glad to hear that i.landsat.rgb works well.

I sort of hesitate to add it to CVS since it could be
"easily" added to r.colors.

I cc to grass-dev to seek for a solution. The only
real missing function in the C library is the possibility
to calculate percentiles from a channel histogram.

Wolf was working on that (percentiles in r.univar) but
apparently it's not complete. The approach could be:

- implement percentiles and related stats in C (gmath?)
- add percentiles to r.univar
- add percentiles to v.univar
- remove r.univar.sh as no longer needed
- remove v.univar.sh as no longer needed
- implement method in r.colors (the LANDSAT color trick is
  to take away 2% of the histogram area from top and bottom)

Having this long term wish "percentiles" implemented in C
would in fact solve a couple of problems (duplicated modules).

I really hope that we can find another capable to help Wolf
(if he's still available).

Markus

On Wed, Mar 15, 2006 at 12:12:23AM -0800, Dylan Beaudette wrote:

Thanks again Markus:

your new i.landsat.rgb script did wonders on these images!

examples:

original made with r.composite:
http://casoilresource.lawr.ucdavis.edu/drupal/node/217

new one made with i.landsat.rgb:
http://casoilresource.lawr.ucdavis.edu/drupal/node/216

Cheers!

Dylan

On 3/14/06, Dylan Beaudette <dylan.beaudette@gmail.com> wrote:
> Ian,
>
> Thanks for the pointers. In the past, I was not performing any
> "enhancements"
> to the landsat scenes as there were so many of them, and they looked good
> enough. However with Markus' latest script, I think that I will re-compile
> arizona! good thing that I hadn't started on Nevada yet!
>
> Cheers,
>
> Dylan
>
> On Tuesday 14 March 2006 12:44 pm, Ian MacMillan wrote:
> > Dylan, I am not sure if you have this problem, but you might want to
> > watch out with the colors when you patch landsat tiles together. The
> > colors tend to get screwy since the the shots were each taken at
> > different times of day, different days of the year, etc. I have found
> > that it is best to enhance each tile separately, then patch them
> > together at the end, rather than patching all band 1's, all band 2's
> > etc. You probably already knew this, but thought I would add my two
> > cents.
> >
> > -Ian
> >
> > On Mar 14, 2006, at 10:04 AM, Dylan Beaudette wrote:
> > > Markus,
> > >
> > > Nice images!
> > >
> > > a couple things:
> > >
> > > 1. the link at the top of the page had some interesting polar plots.
> > > For hard copy I found that ps.rose in the GMT suite produces excellent
> > > results as well:
> > > http://169.237.35.250/~dylan/NPS/day100.png
> > >
> > > 2. the color boost technique -- is your script available on the GRASS
> > > wiki somewhere, or in the grass scripts dir in a recent CVS branch?
> > >
> > > This looks like it will do the trick, now the only problem is that I
> > > have just put together the entire state of Arizona with the poor
> > > looking imagery!
> > >
> > > thanks for the tips,
> > >
> > > Dylan
> > >
> > > On 3/14/06, Markus Neteler <neteler@itc.it> wrote:
> > >> Dylan Beaudette wrote:
> > >>> Hi everyone,
> > >>>
> > >>> I was working on constructing some "true color" landsat composite
> > >>> images today
> > >>> from bands 3,2,1 -- and came across some strange inconsistencies.
> > >>> Data from
> > >>> one source produces "nice" true color images:
> > >>>
> > >>> http://casoilresource.lawr.ucdavis.edu/drupal/node/211
> > >>>
> > >>> whereas, another source produces somewhat muddy true color
> > >>> composites. I tried
> > >>> playing a bit with an equalized grey colormap for each band via
> > >>> r.colors
> > >>> color=grey.eq with the following results:
> > >>>
> > >>> http://casoilresource.lawr.ucdavis.edu/drupal/node/215
> > >>>
> > >>>
> > >>> Does anyone have any tips on how to tweak color ramps for the
> > >>> various bands so
> > >>> as to get a better looking "true color" composite?
> > >>
> > >> how do you like this LANDSAT:
> > >> http://mpa.itc.it/markus/grass61/demos/
> > >> -> LANDSAT 7 color boost
> > >> ?
> > >>
> > >> Markus
> >
> > -------------------------------------------------------------
> > This message has been scanned by Postini anti-virus software.
>
> --
> Dylan Beaudette
> Soils and Biogeochemistry Graduate Group
> University of California at Davis
> 530.754.7341
>
>

--
Markus Neteler <neteler itc it> http://mpa.itc.it
ITC-irst - Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18 - 38050 Povo (Trento), Italy