[GRASS5] reorder points so that little one are in front of big ones in d.vect.chart

[Moritz Lennert]

On Fri, December 17, 2004 0:03, Hamish said:
>> Trying to finish the map on survey responses per country, I have the
>> following problem:
>>
>> I use a vector point file with the centroids of the countries. I have
>> a columns "respondents" in the accompanying dbf file. I display them
>> as proportionate circles using d.vect.chart's 'sizecol' option.
>>
>> However, some of the smaller circles are covered by some of the larger
>> ones. Sorting the dbf file won't make a difference since it is the
>> order of the points in the vector file which is important. So, how can
>> I sort the vector file (or create a new one) in order to have them in
>> the order of size of one attribute column ?
>
>
> possible crappy workaround:
>
> open DBF in OpenOffice, sort, resave.

Just sorting the dbf file does not work, as this does not change the topology
file, and it is the latter that determines order of display. So, for the
records, this is what I did:

- create x and y column in dbf file:

echo "alter table countrypoints add column x double" | db.execute
echo "alter table countrypoints add column y double" | db.execute

- use v.to.db to add the point coordinates to the dbf table:
v.to.db map=countrypoints option=coor col=x,y

- cp this dbf table to the current directory

cp $GISDBASE/$LOCATION_NAME/$MAPSET/dbf/countrypoints.dbf countrypoints2.dbf

- use oocalc on the copy to reorder (in descending order !) according to the
values of the column that determines piechartsize

- use v.in.db to create a new vector point file in GRASS

v.in.db database=./ table=countrypoints2 x="x" y="y" cat="cat" out=countrypoints2

There you go !

>
> better idea: someone fixes d.vect.chart
>

I've had a look at d.vect.chart. If I understand correctly, the pies plotting
is done via the pie() function defined in pie.c. And if I further understand
correctly, it should be enough to sort the Points structure, once all points
have been appended, i.e. after line 50. Points is defined in line 43 by

Points = Vect_new_line_struct ();

So we would need to sort this structure. Before I delve into the source code
and doxygen manual, could someone tell me if sorting functions for qsort
alreay exist for such structures ? And, whether I am on the right path ? ;-)

Moritz