[GRASS-user] Defining color table rules

[Pedro Roma]

Glynn, thanks for your answer. But, for instance in GUI if a select a type
of color table and then I decide to user a rule file, there is no blank
option in "Type of color table". And if I choose rule, it gets an error. So,
in this cases I just have to close r.colors window and open one again. This
may sound a bit unclear .

But thanks
Pedro


> > 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 at gclements.plus.com>
>
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