[GRASS-user] Question about the use of d.vect.thematic

[Hamish]

Thomas wrote:
> I am trying to use d.vect.thematic to create a thematic map
> where the vector polygons are filled with a color dependent
> on an attribute value, swe, which is of type 'real'. I am
> using sqlite as the db driver. The swe attribute was added
> to my vector map using v.db.join, which worked fine. I can
> query the map and see that the swe values are correct.
> 
> However, when I use d.vect.thematic, I get the following
> error:
> 
> Column <swe> is of type <real> which is not numeric.

probable bug in d.vect.thematic which only know integer and
double precision.

> I don't understand; I guess there are subtle nuances with
> these data type considerations which I don't yet appreciate.
> When I created my sqlite db and table, should I have read-in
> the data as a different type? If so, what?


my advice if you have less than 30,000 area features is to use
the new v.colors scripts to add a new GRASSRGB column with
colors, then use 'd.vect -a'. Maybe it is possible to use
d.vect's new zcolor= option, but that is more for points data
than areas.

of course v.colors suffers from the same lack of imagination
and so will need an edit to work with "REAL" types.

look for a line like this:
(v.colors, but d.vect.thematic is similar)

elif [ "$NCOLUMN_TYPE" != "INTEGER" ] && [ "$NCOLUMN_TYPE" != "DOUBLE PRECISION" ] ; then
    g.message -e "Column <$GIS_OPT_COLUMN> is not numeric"
    exit 1
fi


and try adding 

  && [ "$NCOLUMN_TYPE" != "REAL" ]

to the test. (edit to match local conditions)


Hamish