[Freegis-list] Maps and barcharts

[Brent Wood]

--- Jose Gomez-Dans <jgomezdans at gmail.com> wrote:

> Hi!
> We have a lot of data in different formats (shapefiles, tables...). We want
> to move all this data to a database (read: PostGIS) in order to produce the 
> sort of studies we have been producing so far with very labour intensive 
> methods :)

Way to go, that's exactly what I'm trying to do, with reasonable success, here
in New Zealand.

> So far, so good. PostGIS spatial queries are awesome, and coupled with
> Python, 
> Matplotlib and LaTeX, I am producing very good looking reports. However, it 
> is producing adding cartography to this mix. I have in the past used GMT for 
> raster data, and I guess I could convert WellKnownText into something that 
> GMT understands. However, there is a need to produce cartography with pie 
> charts, bar charts and other stuff on them, something like what this image 
> shows: <http://www.redcar-cleveland.gov.uk/YrCounc1.nsf/map-piecharts.gif> 
> (this is just a random example found googling around). Even automatically 
> producing simple maps of vector data coloured by attribute (with a nice 
> legend, scale bar et al.) would be very helpful. 
> 
> Is there some FOSS framework to accomplish this task?


Hi Jose,

This should be of interest....

I have been given access to some $$ to fund the development of an OGR GMT
driver, so PostGIS data can be directly written to GMT format (& vice versa),
using ogr2ogr (also shapefiles, etc). I think this will pretty much accomplish
much of what you are asking.

This project is very recent, and Paul Wessel (GMT developer) has suggested
addressing some of the limits in the way GMT handles vector data, which will
require modifications and header support in GMT vector data files.

I'm discussing this with Paul, after which I'll be posting the proposal to the
GMT mailing list for discussion & comment. 

We want to include basic topology (ie; polygons with holes) and attribute data
for the spatial features in a structure which is bacwards compatible with
existing GMT code. We're probably not that far away.

My funding is limited, so if anyone else is able to contribute in the case of
this revised capability exceeding the amount I have availble, it may be useful
(and give you some say in what we finish up with :-)

I have also used GMT to generate pie charts on maps, looking just a good as
other GMT output. My script iterated through the data fields for each point,
drawing the wedges for each field in separate passes.

If you define your map space by a cartesian space covering your data extent,
GMT can also draw very effectrive graphs & scatterplots. Slightly cumbersome,
but the results are fine.

You could also use the gd primitives to build up graphs, I know the graphs on
www.netcraft.com are done this way (as an example), and they cover a fair range
of outputs.  

You can use ImageMagick to convert these to sun rasters & put them on your GMT
map with GMT.


Cheers,

   Brent Wood



 
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