Pedro Roma wrote:
I'm reading r.colors manual webpage (
http://grass.itc.it/grass64/manuals/html64_user/r.colors.html) and I have a
few questions related with defining new color tables.
1- At color (in Parameters) one of the options is rules. But if i select
rules and insert a path to a rules file I get this error:
*ERROR: "color", "rules", and "raster" options are mutually exclusive*
*
*
Was this suppose to happen?
Yes. If you specify a file for "rules", the "color" option should be
blank.
[color=rules exists for compatibility with previous versions, and only
works from the command-line, not the GUI.]
2- About color tables with absolute values (e.g. NDVI) if a NDVI pixel has
value between 2 defined values, which color does it get?
It's interpolated. This is true whether the rules uses absolute values
or percentages (or a mix of both).
3- About aspectcolr*.* To each category a color is assigned (e.g. white,
yellow bla bla bla). Is there a list of possible colors to assign?
The list of named colours is:
white black red green blue yellow magenta cyan aqua grey gray
orange brown purple violet indigo
You can mix named colours and r:g:b notation freely.
4- Regarding assigning a rules.info to a map (as it's demonstrated in the
same manual page). There are two ways. How come r.colors can use, as an
input, rules.info if it's stated before the r.colors statement.
cat rules.file | r.colors map=threecats color=rules
color=rules reads rules from stdin, which in the above example is the
contents of the rules.file via "cat". The following commands will
all achieve the same result:
cat rules.file | r.colors map=threecats rules=-
r.colors map=threecats color=rules < rules.file
r.colors map=threecats rules=- < rules.file
r.colors map=threecats rules=rules.file
For reading from a file, the last one is preferable (and is the only
one which will work from the GUI). Beyond that, using rules=- is
preferred to color=rules (apart from anything else, rules=- works in
7.0 while color=rules doesn't; color=rules is only kept in 6.4 for
backwards compatibility).
The use of "cat file | ..." rather than "... < file" can be easier to
read if you're creating a long pipeline in a script, as it places the
source file at the far left of the command. The following both have
the same effect:
cat infile | cmd1 | cmd2 | ... | cmdN > outfile
cmd1 < infile | cmd2 | ... | cmdN > outfile
but the former is probbably clearer.
5- One last question 
I tried to display the color table associated with a
raster map layer (d.colortable) but I get the following message:
Command 'd.colortable' not yet implemented
Odd; you can try d.legend instead, or use r.mapcalc to create a test
map to which you can assign the colour table.
--
Glynn Clements <glynn@gclements.plus.com>