[GRASSLIST:3669] Re: v.extract (5.7) doesn't work on extra fields?

[William K]

On Jun 15, 2004, at 9:48 AM, Radim Blazek wrote:

> 1) It is not guranteed that pairs cat-POLYID in tgr_2 and tgr_3 are
>    identical. It seems that in this case it is true but you should not
>    rely on that.
>
I guess this is a result of there being no guarantee that TIGER records 
are sorted by CENPOLYID.  There is a 1-1 relationship between fields 2 
& 3 by CENPOLYID.  Maybe this should be taken care of in the 
conversion? - sorting TIGER records by an appropriate unique ID (TLID 
or CENPOLYID).

Maybe I'll do a join by CENPOLYID after conversion, just to get the 
Polygon attribs into the centroid field.

> 2) There are no elements with category of field 4, if you link a table
>    to field 4, it has no effect, you could overwrite the link of
>    field 3, but that is not secure as I said above.
>
So there are specific associations of field numbers and GRASS geometry? 
  or something like that?  like 1=boundaries, 2=centroids/areas?  3 is 
extra? or what?

I had problems understanding the old vector cat/label thing, I guess 
I'm still not quite getting the new system.  Probably my ArcInfo 
background getting in the way.

> 3) > v.extract -d in=tgr out=tgrzip type=area,centroid field=4 
> list=1-99999
>    This is wrong as it groups areas by category, not by ZIP.
>
so v.extract -d works purely on categories?  I guess I was thinking 
that cats were like a table relate to the fields, and it would use the 
field columns (minus the cat).

> 4) There was a bug in v.extract -d, I fixed that in cvs.
>
I'm using CVS snapshots (2004-6-5 at that time).  I had heard about the 
bug fix and wanted to try it out.

> 5) ZCTA5 is varchar and v.reclass does not work with varchar column.
>
> Here is an example how to do that (Postgres, MySQL will be similar),
> I know that it is not simple solution for simple task,
> support for varchar columns and dissolve option in v.reclass
> should make it easier:
>
> v.in.ogr -o dsn=TGR37013/  layer=CompleteChain,PIP,Polygon output=tgr1 
> \
>             type=boundary,centroid snap=-1
>
> echo "create table tgr1_4 as select distinct ZCTA5 from tgr1_3" | 
> db.execute

so far, what I've done.  oh, wait, distinct.

> echo "create table tgr1_5 as select tgr1_2.cat, tgr1_3.ZCTA5, 
> tgr1_4.oid
>       as zcta5id  from tgr1_2, tgr1_3, tgr1_4 where tgr1_2.POLYID = 
> tgr1_3.POLYID
>       and tgr1_3.ZCTA5 = tgr1_4.ZCTA5" | db.execute
>
now I need to pause to wrap my head around this - kinda slow on SQL 
selects still....

....so: _2.cat -> (POLYID) -> _3.ZCTA5 -> (ZCTA5) -> _4.oid (giving 
each unique ZIP an integer)

> v.db.connect -o map=tgr1 table=tgr1_5 key=cat field=2
>
> v.reclass input=tgr1 output=tgr2 field=2 col=zcta5id type=area
>
> v.extract -d in=tgr2 out=tgr3 type=area list=0-10000000 new=-1
>
weeeeeeee!  at least I can script all this.  so, the cat of tgr3 
(dissolved) relates back to the record number of tgr1_5, right?  I 
guess I could rejoin the tables from there to create something 
exportable with ZCTA5 column...

Thanks, I'll give this a try sometime (kinda busy right now ^_^).

> Radim
>
>
>
> On Wednesday 09 June 2004 20:08, William K wrote:
>> Here's what I've done so far (ultimately I want to test dissolve TIGER
>> polygons by ZIP code):
>>
>> - use native GRASS 5.7 geometry, and store attribs in MySQL (so I can
>> do some table cleanup).
>> - import TIGER CompleteChain, PIP, Polygon layers, with type boundary
>> and centroid.
>> - now I have 3 fields - the 3rd is extra polygon attributes, where the
>> ZIP codes are
>> - use SQL copy to create a new table from field 3 with cat and ZCTA5
>> columns only
>> - register new table with GRASS vectors as field 4
>> - extract with dissolve:
>>
>>    v.extract -d in=tgr out=tgrzip type=area,centroid field=4 
>> list=1-99999
>>
>> and I get 0 everything output.
>>
>> I've tried type=boundary,centroid and boundary,area,centroid.
>> I've tried where="cat > 0" instead of a list.
>> I've tried without dissolving, just to see if I could get anything.
>>
>> If I leave out the field I get a copy of all areas/centroids and field
>> 1 (the boundary attribs), which is not quite as expected (for areas 
>> I'd
>> expect field 2, the area/centroid attribs), but it's something.  And
>> nothing is dissolved of course since all attribs are unique.
>>
>> So, ignoring the dissolve option for now (just testing), nothing is
>> getting selected when a field other than 1 is used.
>>
>> Bug?  Am I missing something?  The imported TIGER vector seem to be OK
>> - v.info reports boundaries, areas and centroids and vector level 2.
>>
>> -----
>> William Kyngesburye <kyngchaos at charter.net>
>> http://webpages.charter.net/kyngchaos/
>>
>> "Time is an illusion - lunchtime doubly so."
>>
>> - Ford Prefect
>
>
-----
William Kyngesburye <kyngchaos at charter.net>
http://webpages.charter.net/kyngchaos/

"Mon Dieu! but they are all alike.  Cheating, murdering, lying, 
fighting, and all for things that the beasts of the jungle would not 
deign to possess - money to purchase the effeminate pleasures of 
weaklings.  And yet withal bound down by silly customs that make them 
slaves to their unhappy lot while firm in the belief that they be the 
lords of creation enjoying the only real pleasures of existence....

- the wisdom of Tarzan