[GRASS-user] Multiple to one question

[Adam Dershowitz, Ph.D., P.E.]

--Adam



On Apr 15, 2009, at 9:29 PM, Adam Dershowitz, Ph.D., P.E. wrote:

>
> 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?
>
>

It seems like I should be able to edit the cats, and I tried a few  
different things with v.edit, but I have not had any luck.  I tried  
some things like this:
v.edit map=foo tool=catdel -r where="cat > 0"
but it gives me:
ERROR: Tool catdel requires option cats
Although the above seems to work with tool=select, which I was using  
to test things about before doing the delete.

I copied my original vectors, and created the view.  Now what I want  
to do is to delete all the categories in this vector that point to  
null.  Is there a way to do that?

Thanks,

--Adam