[GRASS-dev] [grass-code R][506] v.what.rast should be able to use other methods like bilinear

[William A. Perkins]

Maciej,


>>>>> "Maciej" == Maciej Sieczka <tutey at o2.pl> writes:

    Maciej> grass-dev at grass.itc.it wrote:
    >> v.what.rast does what I need, but only with nearest
    >> neighbor sampling.  I could use v.sample, but that
    >> creates a new map/table, and the only way to get the
    >> attribute back to the original map is to use an SQL join,

    Maciej> William,

    Maciej> For a workaround, you can also link the output vector's
    Maciej> datatable to another layer in the input vector; sth like:

    Maciej> $ v.sample -b input=pts_in col=value out=pts_out rast=xxx
    Maciej> $ v.db.connect map=pts_in driver=dbf table=pts_out layer=2

This is a very good idea.  I will start doing this.  

    Maciej> BTW - anybody knows how to just copy a column from table to
    Maciej> table? Or update an existing column in one column with the
    Maciej> content of a column in another table? That's be the easiest
    Maciej> workaround.

What I usually end up doing is temporarily connecting to a Postgres
database, for which this statement works (in your example):

  UPDATE pts_in SET value = pts_out.rast_val 
  FROM pts_out
  WHERE pts_in.cat = pts_out.cat;

However, I try to avoid keeping attributes in Postgres because I
access by GRASS databases from a variety of computers, some of which
do not have access to the Postgres server. 

    >> which is unsupported in dbf and sqlite databases.

    Maciej> SQLite supports JOIN AFAICT. Does it fail in GRASS? Can you
    Maciej> provide a test case?

The documentation says it's supported, and I have only been able to do
joins with SELECT, but not UPDATE.  The way I read the SQLite
documentation, I should be able to do this:

    UPDATE pts_in SET value = pts_out.rast_val WHERE pts_in.cat = pts_out.cat;

(sqlite does not allow a FROM clause in UPDATE).  But I've never
gotten that to work.  I worked up a little example for which I've
attached the output.  I was working with today's CVS and on Mac OS X.  

    >> Furthermore, IMHO, v.rast.what should,
    >> through options,  do whatever v.sample does and v.sample
    >> should be be eliminated.

    Maciej> I have added the suggestion to GRASS 7 ideas on WIKI.

Thanks.

    Maciej> Maciek

Bill

-- 
Bill Perkins
Pacific Northwest National Laboratory
Environmental Technologies Division, Hydrology Group
P.O. Box 999 MSIN K9-36
Richland, Washington, USA  99352
voice: (509) 372-6131 fax: (509) 372-6089 email: william.perkins at pnl.gov

-------------- next part --------------
GRASS 6.3.cvs > db.connect -p
driver:sqlite
database:$GISDBASE/$LOCATION_NAME/$MAPSET/sqlite.db
schema:
group:

GRASS 6.3.cvs > cat junk.sql
drop table tmp1;
drop table tmp2;
create table tmp1 ( cat integer, num integer );
insert into tmp1 ( cat, num) values (1,1);
insert into tmp1 ( cat, num) values (2,2);
insert into tmp1 ( cat, num) values (3,3);
insert into tmp1 ( cat, num) values (4,4);
create table tmp2 ( cat integer, num integer );
insert into tmp2 ( cat, num) values (1,5);
insert into tmp2 ( cat, num) values (2,6);
insert into tmp2 ( cat, num) values (3,7);
insert into tmp2 ( cat, num) values (4,8);

GRASS 6.3.cvs > db.execute -i --v < ~/tmp/junk.sql  

GRASS 6.3.cvs > echo 'select tmp1.cat, tmp1.num, tmp2.num from tmp1, tmp2 where tmp1.cat = tmp2.cat' | db.select output=',' vs=''
cat,num,num
1,1,5
2,2,6
3,3,7
4,4,8

GRASS 6.3.cvs > echo 'update tmp1 set num = tmp2.num where tmp1.cat = tmp2.cat' | db.execute
DBMI-SQLite driver error:
Error in sqlite3_prepare():
no such column: tmp2.num

ERROR: Error while executing: 'update tmp1 set num = tmp2.num where
       tmp1.cat = tmp2.cat
       '

GRASS 6.3.cvs > db.connect driver=pg database=template1

GRASS 6.3.cvs > db.connect -p
driver:pg
database:template1
schema:
group:

GRASS 6.3.cvs > db.execute -i --v < ~/tmp/junk.sql
DBMI-Postgres driver error:
Cannot execute:
drop table tmp1
ERROR:  table "tmp1" does not exist


WARNING: Error while executing: 'drop table tmp1'
DBMI-Postgres driver error:
Cannot execute:
drop table tmp2
ERROR:  table "tmp2" does not exist


WARNING: Error while executing: 'drop table tmp2'

GRASS 6.3.cvs > echo 'select tmp1.cat, tmp1.num, tmp2.num from tmp1, tmp2 where tmp1.cat = tmp2.cat' | db.select output=',' vs=''
cat,num,num
1,1,5
2,2,6
3,3,7
4,4,8

GRASS 6.3.cvs > echo 'update tmp1 set num = tmp2.num from tmp2 where tmp1.cat = tmp2.cat' | db.execute
 
GRASS 6.3.cvs > echo 'select tmp1.cat, tmp1.num, tmp2.num from tmp1, tmp2 where tmp1.cat = tmp2.cat' | db.select output=',' vs=''
cat,num,num
1,5,5
2,6,6
3,7,7
4,8,8