d.vect

[Darrell McCauley]

Srin (srin at brcsun0.tamu.edu) writes on 19 Jul 93:

>I am wondering will there be enough interest to make the v.digit
>program to display in different colors for each category, either line or
>polygon.

YES YES YES.

not only v.digit, but a standalone program as well. In fact, 
I would recommend something standalone first, then, if it's
a hit, modify v.digit.

don't forget other types (e.g., point).

I'm not sure if this exists, but how about a masking program too:
 (extract all area-edges with category 3 in the file "big")
 v.extract cat=3 type=a input=big output=small
  
 type=[a|l|p|whatever other types are defined]
 cat=n (option parameter restricting to a certain category)

or maybe you want relations other than "equal to"
(e.g., "greater than")

Even if this capability does exist, a display program should
have options like this:

 d.vect.srini cat=3 color=red [[cat=4 color=blue] [cat=5 color=green]
 d.vect.srini type=area

(a separate file should not have to be created just to show
types that are a certain category).

Suppose that you have a vector file of Texas rivers. In it, you have 
labeled lines with chemical concentration. Then,

 d.vect.srini color=red relation=greater cat=70 vect=rivers
 d.vect.srini color=blue relation=less cat=50 vect=rivers

would show all segments with X > 70 ppm in red 
       and all segments with X < 50 ppm in blue.

I, for one, would like to see more vector support, and excellent
programmers like yourself could probably do this easily with the
proper motivation/encouragement - GO FOR IT! ;-)

(Send your cards/cookies to Srini!)

>What are the problems if one uses $LOCATION/colr to store the color
>information for a vector map cateogories.

I don't see any offhand, but you may want to have the option
of overriding this (as shown above) without mucking around with
a colortable.

Also, there should a way for programs that specify color
to use something other than the 8 or so "standard" colors.
E.g., specify an RGB triple or perhaps incorporate a 
standard colorname lookup like X11 (rgb.txt). That way,
programs like d.erase, d.graph, etc could use more colors.
But I digress...

>Is it possible to do the above with the present data structures, if no,
>what are likely problems to be encounted?

I believe so (in my limited vector programming experience). If
we want to talk code, let's move this to grassp.

>Srinivasan

--Darrell