[GRASS5] [bug #4037] (grass) d.vect.thematic: fails to generate a legend for >20 custom_breaks

[Hamish]

> Thinking about this on the commute to work this morning, I came up
> with an idea for a longer-term way to deal with vector thematic
> mapping and legends. For vectors, I can't think of a situation where a
> legend is NOT used for some kind of thematic mapping, even if there is
> a legend item for each vector object. That is, it is somewhat
> different from raster legends for floating point maps. So here is my
> idea that builds on the unique multi-layer vector architecture for
> GRASS.

The data I work with is often a swarm of vector points. e.g. bathymetric
soundings or a trail of measurements (e.g. temperature) along a line of
gps track points. In these cases a pseudo-continuous legend (like
d.legend for floating point) is preferable. Currently I calculate RGB
values in Matlab during post-processing and place in a GRASSRGB column,
but this is unpractible for e.g. LIDAR data where there can be no table.
Automatic would be better.

d.vect.thematic doesn't have to support this, but a use case to
consider..

As was earlier suggested on the list, reusing the r.colors colr/ files
for vectors would be neat. Only thing to check is that the functions
that query the color don't need a raster to be open. i.e. the
vector/display libs can't depend on the raster lib.



Hamish