On 25/03/09 11:05, Craig Leat wrote:
Hello
I have a vector map with points representing latrines and each point
has an attribute describing the place name. I ran v.edit to snap
points with a threshold of 5m
Because you think that these points are actually duplicates, or because
you want the information about all latrines within a certain radius to
be regrouped ?
and v.info reports 7296 features for the
cleaned map. I now wish to count the number of latrines in each place,
so I ran:
echo "SELECT *,count(Area) FROM MT_San_clean GROUP BY Area" | db.select
and get a total of 10537, so the results are bogus.
Running the following command I can see the reason for the bogus results:
v.category in=MT_San_clean opt=print
1331/566/571/691/1332/456/416/410/405/561/390
1294/1249/1265/1229/1225/1273/1233
v.edit has assigned multiple categories to points when they were snapped.
To get a meaningful count of points by Area I can think of two solutions:
1) Use awk to filter out the first category for each feature from the
output of v.category opt=print and feed this list of cats into
db.select,
however I'm not sure of the sql syntax for WHERE "cat=MyListOfCats".
Create a table MyCats containing your cats and the use WHERE "cat in
(select * from MyCats)"
2) Use awk to filter out all, but the first category for each feature
from the output of v.category opt=print and feed this list of cats
into v.category opt=del,
however I'm not sure of the relationship between feature ids and cats,
and v.category wants a list of ids.
use v.edit select= cats= to find out ids.
Can someone please suggest an easier way or give me a pointer to
implement either of my ideas?
How about v.edit catdel= cats= ?
Or v.clean tool=rmdupl (although the man page says "pay attention to
categories!" - don't know what that means).
Moritz
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