[GRASS-user] setting a color value to transparent

[Chris Bartolomei]

 Hi Vero - thanks for the idea. The quick and dirty fix was to just create a new map with just the features I want to show. I need to experiment a bitt o see what else can work but as usual with work - not enough free time to find the right solution. :(  We are stuck with the GRASS version for now ... it takes forever to get software updates approved! (clearly) ... but 7.8 is working it's way through the approval process.
:)Chris

    On Sunday, April 25, 2021, 10:56:13 AM EDT, Veronica Andreo <veroandreo at gmail.com> wrote:  
 
 Hi Chris, 

Would choosing the categories (cat values) of features you want displayed help? AFAIU from the ps.map manual, it is possible to select cats to be displayed. Also, there's the possibility to use a where clause.
Just out of curiosity: why are you still running GRASS 7.4? We are at 7.8.5 already with python 3 support and soon to release GRASS 8.0 ;)
Best, 
Vero

El vie, 23 abr 2021 a las 20:19, Chris Bartolomei via grass-user (<grass-user at lists.osgeo.org>) escribió:

Good afternoon all,
I have a polygon map with a handful of features, I've added a column I use for setting RGB values "RRR:GGG:BBB" to color them. I use three (3) colors - red, orange, and yellow - but I would like some of them to be transparent but I can't find anywhere in the manuals what the code would be for transparent. Searching Google-land I see there's an RGBa standard which can set tranparency but GRASS doesn't seem to support that. I've tried setting the value to NULL, to "", to "none", and tried "0:0:0:0" (RGBa) all to no avail ... 
I am using ps.map to create an image so the ps rules file tells GRASS to use the RGB column to define the colors ... I believe I'm stuck with this methodology for now.Am I going to have to select the features which I do want colored and make a new map with just those features? or do I have to remove the postscript command for the RGB column and create a color table then reset my category values to 1, 2, 3, or 4 using a color table something like:  nv white  1 red  2 orange  3 yellow  4 white
  end
I was hoping to avoid creating a color table and changing the category values as this map gets modified twice a day... It's running in GRASS 7.4 on Linux ... 
Thanks and happy weekend!:)
Chris
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