[postgis-users] Newbie ST_World2RasterCoordX, ST_World2RasterCoordY Band Values nested loop to iterate over raster

[Chris English]

Some progress:
extract_as_text_5(rast raster)
--snip
v_param raster;

Begin
for i in 1..2048 loop
for j in 1..1536 loop
select ST_world2rastercoordx(v_param, i, j) as xcoord,
St_world2rastercoordy(v_param, i, j) as ycoord,
-snip
Select extract_as_text_5(rast)
from rbike_all;

ERROR:  query has no destination for result data
HINT:  If you want to discard the results of a SELECT, use PERFORM instead.
CONTEXT:  PL/pgSQL function "extract_as_text_5" line 9 at SQL statement

I thought the   ST_xxx( ) as name was providing destination(s).  And perhaps
you
did Not mean to replace rast with v_param inside the loops.

and hoped to get:
     xcoord        ycoord      R    B    G
 large #            large#       1   255  255
and etc.

I see its a name collision, but ...Results so far

On Sat, Jul 9, 2011 at 1:44 PM, Nicolas Ribot <nicolas.ribot at gmail.com>wrote:

> On 9 July 2011 19:00, Chris English <emailchrisenglish at gmail.com> wrote:
> > Hi,
> > I am trying to iterate over a raster, extract World2RasterCoordX/Y and
> Band
> > Values using the following function:
> > Create or replace function extract_as_text(rast raster) returns text as
> > $$
> > Declare
> >  i int;
> >  j int;
> > rast raster;
> > Begin
> > for i in 1..2048 loop  --dim x
> > for j in 1..1536 loop -- dim y
> > select ST_world2rastercoordx(rast, i, j) as xcoord,
> > St_world2rastercoordy(rast, i, j) as ycoord,
> > ST_value(rast,1, i, j) as R,
> > ST_value(rast, 2, i, j) as G,
> > ST_value(rast, 3, i, j) as B
> > from rbike_all;
> > End loop;
> > End loop;
> > return xcoord,ycoord,R,G,B; <- this part is probably not right either -
> > should perhaps just say text
> > end;
> > $$
> > Language 'plpgsql'
> > Query returned successfully with no result in 15 ms.
> > Select extract_as_text(rast)
> > from rbike_all;
> > ERROR:  column reference "rast" is ambiguous
> > LINE 1: select ST_world2rastercoordx(rast, i, j) as xcoord,
> >                                      ^
> > DETAIL:  It could refer to either a PL/pgSQL variable or a table column.
> > QUERY:  select ST_world2rastercoordx(rast, i, j) as xcoord,
> > St_world2rastercoordy(rast, i, j) as ycoord,
> > ST_value(rast,1, i, j) as R,
> > ST_value(rast, 2, i, j) as G,
> > ST_value(rast, 3, i, j) as B
> > from rbike_all
> > CONTEXT:  PL/pgSQL function "extract_as_text" line 9 at SQL statement
> >
> > ********** Error **********
> > ERROR: column reference "rast" is ambiguous
> > SQL state: 42702
> > Detail: It could refer to either a PL/pgSQL variable or a table column.
> > Context: PL/pgSQL function "extract_as_text" line 9 at SQL statement
> > Removing rast from Declare above  results in the same error.
> > Any pointers greatly appreciated.
> > Chris
> >
> Hi Chris:
>
> Both the input parameter and the declared parameter are called "rast".
> This causes the error I think.
> Rename the input parameter to something like p_rast and the declared
> parameter to v_param.
>
> That should fix the problem.
>
> Nicolas
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>



-- 
He doesn't fully understand what he thinks he knows about the problem.
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