[GRASSLIST:876] Re: GMT / GRASS use / shp2gmt

[Allan Hollander]

Trevor,

I'm a rank beginner at GMT but in my one exercise to date with it I
learned the following. Mark Fenbers has modified the shp2gmt.c file to
include the attribute info from the dbf file into the multi-segment
separator of the psxy input file. His code is given in his message here:  
http://www.mechanik.tu-darmstadt.de/GMT-Help/Archiv/11021.html.

The output from his shp2gmt version looks like this for a tiny extract 
from a state map of the US:

>       Polygon #0      nVertices=17    nParts=1        cat=2   AREA=0  PERIMETER=0.224 STATESP020=3    STATE="Alaska"  STATE_FIPS="02"  
-2.86129e+06    6.01613e+06
-2.86152e+06    6.01607e+06
-2.86163e+06    6.01615e+06
-2.86178e+06    6.01631e+06
-2.86248e+06    6.01724e+06
-2.86327e+06    6.01807e+06
etc.

What I can then do is write an awk script to substitute in the correct
-G and -W plotting parameters depending on the attributes. For instance
running this bit of awk over the above input file

{if ($0 ~ /Alaska/) printf "> -G175 -Wblack\n";
else print;}

should transform it into an input file where Alaska is plotted with a grey 
fill. With more complicated lookups in the awk script, one can do pretty 
sophisticated thematic mapping using this approach.

Best wishes,

Allan Hollander

---

On Tue, 25 Apr 2006, Trevor Wiens wrote:

> Grudgingly I'm using GMT after working through Dylan's example and am
> getting it to be somewhat functional.
> 
> I will be needing to script the building of a large number of maps
> which I may store either in PostGIS or GRASS. 
> 
> I've noticed in the use of shp2gmt that there is no way of adding in a
> z attribute for use with the thematic colour assignment feature in GMT.
> If necessary I can extract bits based on different attributes and add
> them in separately, but it would be nice to be able to simply define a
> colour them once and be done with it. Any suggestions on how I can turn
> an attribute column in GRASS into a z-element that will be converted
> with shp2gmt would be appreciated.
> 
> T
> 

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