Details Ticket 1470


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Serial Number 1470
Subject full floats support for r.colors, please
Area wish
Queue grass
Requestors peter.loewe@gmx.de
Owner mlanda
Status resolved
Last User Contact Tue Oct 9 18:48:02 2007 (1 yr ago)
Current Priority 30
Final Priority 70
Due No date assigned
Last Action Tue Oct 9 18:48:02 2007 (1 yr ago)
Created Thu Dec 5 12:34:54 2002 (6 yr ago)

Transaction History Ticket 1470


Thu, Dec 5 2002 12:34:54    Request created by guest  
Subject: full floats support for r.colors, please

Platform: GNU/Linux/i386
grass obtained from: Trento Italy site
grass binary for platform: Compiled from Sources
GRASS Version: 5.00

Wouldn't it be awfully nice to have r.colors color=grey.eq|grey.log|random etc
working for rasters of floats?

Peter
Thu, Dec 5 2002 15:18:25    Mail sent by neteler@itc.it  
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Date Thu, 5 Dec 2002 15:18:22 +0100
From Markus Neteler <neteler@itc.it>
To Request Tracker <grass-bugs@intevation.de>
Subject Re: [GRASS5] [bug #1470] (grass) full floats support for r.colors, please
Message-ID <20021205151822.O7895@itc.it>
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On Thu, Dec 05, 2002 at 12:34:54PM +0100, Request Tracker wrote:
> this bug's URL: http://intevation.de/rt/webrt?serial_num=1470
> -------------------------------------------------------------------------
> 
> Subject: full floats support for r.colors, please
> 
> Platform: GNU/Linux/i386
> grass obtained from: Trento Italy site
> grass binary for platform: Compiled from Sources
> GRASS Version: 5.00
> 
> Wouldn't it be awfully nice to have r.colors color=grey.eq|grey.log|random
etc working for rasters of floats?
> 
> Peter

Right. You are kindly invited to help with that :-)

Markus


Tue, Mar 11 2003 10:45:53    Mail sent by mneteler  
Could you try the 

1.  r.recolor - this new program allows to make color management for 
raster map using categories distribution in equal area mode  and 
generate desiring color levels using extended possibilities  for linear 
color interpolation or file color sets. The program works with FP maps  
and has description (file DESCRIPTION in folder with program). This 
program is very usefull to us because able to show maps with different 
kinds of histograms. We hope it will be usefull to others.


available in
http://grass.itc.it/outgoing/SJGeo.tar.gz  

and report to 'grass5'? 

Markus

Tue, Feb 27 2007 17:41:07    Taken by mlanda  
Thu, Oct 4 2007 17:19:27    Mail sent by msieczka  
guest wrote (Thu, Dec 5 2002 12:34:54):

> Wouldn't it be awfully nice to have r.colors color=grey.eq|grey.log|random
etc
> working for rasters of floats?

Glynn added flags -e and -g to to r.colors few weeks ago, which allow to
equalize any color table now, and floating point rasters are supported too.
An outstanding issue is 'random' colortable for floating point rasters. I
don't if this is possible. Still only integer rasters are supported.

Maciek
Sun, Oct 7 2007 05:07:19    Mail sent by hamish_nospam@yahoo.com  
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Date Sat, 6 Oct 2007 20:07:11 -0700 (PDT)
From Hamish <hamish_nospam@yahoo.com>
Subject Re: [GRASS-dev] [bug #1470] (grass) full floats support for r.colors, please
To Maciek Sieczka via RT <grass-bugs@intevation.de>, peter.loewe@gmx.de
Cc grass-dev@grass.itc.it
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Maciek Sieczka wrote:
> An outstanding issue is 'random' colortable for floating point rasters. I
> don't if this is possible. Still only integer rasters are supported.

you could do it by splitting into ranges first, e.g. like r.stats or
d.histogram's nsteps= option.


Hamish



       
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Sun, Oct 7 2007 16:43:41    Mail sent by glynn@gclements.plus.com  
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To Hamish <hamish_nospam@yahoo.com>
Cc Maciek Sieczka via RT <grass-bugs@intevation.de>, peter.loewe@gmx.de, grass-dev@grass.itc.it
Subject Re: [GRASS-dev] [bug #1470] (grass) full floats support for r.colors, please
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Hamish wrote:

> > An outstanding issue is 'random' colortable for floating point rasters. I
> > don't if this is possible. Still only integer rasters are supported.
> 
> you could do it by splitting into ranges first, e.g. like r.stats or
> d.histogram's nsteps= option.

You can even use the map's quantisation rules.

But the main issue is whether it's sensible to assign a random colour
table to an FP map. IMHO, a random colour table only makes sense if
the number of categories is small.

If there are many categories (e.g. an integer DEM), it's likely that
the "clusters" of adjacent, same-valued cells will actually be
individual cells. In that situation, a random colour table will just
give you "snow".

A secondary consideration is that a random colour table requires one
rule for each category, which can result in very large colour tables,
which can be slow to create (IIRC, the time taken to create a colour
table is proportional to the square of the number of entries).

IOW a random colour table only makes sense if the data consists of
discrete categories rather than a scalar value. Integer maps can be
either categories or scalars, but FP maps are always scalars.

-- 
Glynn Clements <glynn@gclements.plus.com>


Tue, Oct 9 2007 18:48:02    Status changed to resolved by msieczka  
Tue, Oct 9 2007 18:48:02    Mail sent by msieczka  
glynn@gclements.plus.com wrote (Sun, Oct 7 2007 16:43:41):

> IOW a random colour table only makes sense if the data consists of
> discrete categories rather than a scalar value. Integer maps can be
> either categories or scalars, but FP maps are always scalars.

In that case I'd call the case closed. If anybody minds please re-open the ticket.
Maciek
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