On Apr 15, 2009, at 4:29 PM, Moritz Lennert wrote:
On 16/04/09 01:00, Adam Dershowitz, Ph.D., P.E. wrote:
This is somewhat a followup to my prior post and somewhat a new,
but related problem.
I ended up doing what I had proposed, which is I have a table that
has each sample value and location:
Location Value cat
a 3.1 1
b 2.1 2
a 1.1 3
c 4.1 4
etc.
Then I have linked each vector point to multiple categories by using
v.edit map=foo layer=1 where="cat==1" type=point tool=catadd cat=3
(for example) So then I have an vector point that has a cat of
both 1 and 3. So far so good.
If I then try to display Label vectors using Value for the
attribute, it works fine. Each value is displayed separated by a
slash "/".
The problem is if I try to use a SQL query, it is not working as
expected. I think that what it is doing is just applying the test
to the first value, then showing or hiding the other values based
on that first test (although I am not 100% sure that is what it is
doing).
So, for example, if I were to do Use SQL query: Value > 2.0 it
would draw a label like this: 3.1/1.1 And if I were to use a
query of Value < 2.0 it would not display anything. What I want it
to do is to show all values that are actually greater than 2. and
not to display the others.
Any suggestions of what it is doing, or what I can do about it?
Create a view in your database containing the results of your query,
including cat values, and link your map to that view, instead of the
table. If you want to change the content, just drop the view and
recreate it with a different query. You can do all this either
directly in sqlite, or via the db.execute GRASS module.
Moritz
I really liked the suggestion, so I tried it....but it doesn't work.
To continue my simple example, I did create view less2 cat,Value from
data where Value < 2;
So I end up with a view, as expected.
The problem is that if I now link my map to that view, I get an
error: No attribute found for cat 1 (since the object still tries to
link to 1). And, the same for 2 and 4. And, I still see the points
and slashes (ie it still draws point a and puts a null value then a
slash then 1.1.
So is there a way to have it not draw a symbol and not draw "null
text" when it can't find an attribute? Since, the whole point of what
I am trying to do in this case is to eliminate certain data with a
query?
Thanks,
--Adam
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