[GRASS-dev] new version of d.vect.chart

Michael Barton michael.barton at asu.edu
Tue Oct 10 11:06:33 EDT 2006

This is very nice. Thanks for doing this.

Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

> From: Moritz Lennert <mlennert at club.worldonline.be>
> Date: Tue, 10 Oct 2006 14:27:42 +0200
> To: Grass Developers List <grass-dev at grass.itc.it>
> Subject: [GRASS-dev] new version of d.vect.chart
> Hello,
> Thanks to the help of Radim, Daniel, Glynn and Hamish I have finally
> finished a revised d.vect.chart which offers the following improvements
> over the original:
> - speed: using a map with over 20.000 charts, it takes only half the
> time with attributes in postgresql and only 10-15% of the time with data
> in dbf. With ~600 charts it takes about 60% of the time in both cases.
> This might be different if your map is linked to a table containing many
> more lines than there are objects in the map, since this version loops
> through the entries in the table, instead of looping through the vector
> objects. You can however use the where clause to limit the amount of
> lines retrieved.
> - ordering of charts: if sizecol is used, charts are now ordered so that
> largest are at the bottom
> - choice in proportionality: a new flag allows to make the chart's area
> proportional to sizecol and not the chart's diameter (by using the
> square root of sizecol)
> - where clause: you can limit the objects displayed through a where clause
> - multiple objects with same cat: the module now prints a warning if it
> finds multiple objects with the same cat. In most usages of charts I can
> think of, you don't want to display the same chart twice, only because
> your area of reference might be divided into several polygons (e.g.
> total population of Canada displayed for every single island of the
> country).
> The module uses the new (today) Vect_cidx_find_all() function, so it
> only compiles if you have the latest version of lib/vector/Vlib/cindex.c
> and include/Vect.h. Also, if you use the dbf data backend, you need the
> new support for ASC/DESC in ORDER BY clauses also committed today.
> At this stage, the module draws more than one chart at the same location
> if there is more than one line with identical cat, data columns and size
> column. I wanted to use a SELECT DISTINCT clause, but DISTINCT is not
> supported by the dbf backend, yet. It would be possible to solve this
> within the module, but it might be more interesting to implement a
> DISTINCT clause.
> My question now is: should this replace d.vect.chart in CVS head ? It is
> completely backwards compatible in terms of parameters, with only the -s
> (use square root) added. Or should this live as d.vect.chart2 for a
> while for testing (the attached directory compiles the modules as
> d.vect.chart2) ? Should I commit it to CVS ?
> Moritz

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