I do have another novice question, if I may.
I have a non-geographical object whose shape is defined by
coordinates. These coordinates not ony establishe the shape of the
object but also the objects relative size and its position on the canvas.
Is there a method of using just the shape of the object dynamically
resizing it and choosing its placement on the canvas?
Bob Pawley
www.automatingdesign.com <http://www.automatingdesign.com>
----- Original Message -----
*From:* Obe, Regina <mailto:[EMAIL PROTECTED]>
*To:* PostGIS Users Discussion
<mailto:[email protected]>
*Sent:* Thursday, May 01, 2008 5:19 AM
*Subject:* RE: [postgis-users] Line To Path
I wouldn't quite call it runnning the function in that table.
Basically the SQL statement will create a temporary or in memory
table so to speak. So short answer - yes it is correct - no need
to create a new table or geometry column. Sometimes you may want
to if you use it often or you are grouping many geometries since
the planner has to recalculate each time if it is a dynamic query
as below or view (a saved dynamic query as Kevin pointed out in
last post) .
Well there should be an alias there otherwise it usually will just
alias it as something dumb like ST_Union - so let me correct my
mistake.
SELECT somefield, ST_Union(the_geom) as newgeom
FROM sometable
GROUP BY somefield;
If you wanted to materialize it, I tend to do something like
SELECT somefield, ST_Union(the_geom) as newgeom
INTO somenewtable
FROM sometable
GROUP BY somefield;
A lot of people do
CREATE TABLE somenewtable As
SELECT somefield, ST_Union(the_geom) as newgeom
FROM sometable
GROUP BY somefield;
But I tend to avoid that second syntax since its not as portable
as option 1 (from DBMS to DBMS at least the DBMS I tend to deal
with) and the speed is the same. Granted
I guess the second version is a bit clearer.
Hope that helps,
Regina
------------------------------------------------------------------------
*From:* [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] *On Behalf
Of *George Silva
*Sent:* Wednesday, April 30, 2008 10:47 PM
*To:* PostGIS Users Discussion
*Subject:* Re: [postgis-users] Line To Path
In the same trailing of that question and the answer, that select
statement would run the function st_union in that table, without
the need to create a new table or geometry column?
Sorry to use this post for this, just tought its a quite novice
question, so more people could use the answer.
Thx
Att.
George
On Wed, Apr 30, 2008 at 7:20 PM, Paragon Corporation <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
Bob,
If I understand you correctly, I think you want to use one of
the following
SELECT somefield, ST_Union(the_geom)
FROM sometable
GROUP BY somefield
So lets say you want to collapse 3 rows into 1 then you just
need to group
by some common field.
E.g. if somefield = 1 for your 3 records, then those would get
rolled into
the same record.
The above will give you a LINESTRING or MULTILINESTRING. If
you have all
LINESTRINGS, then may be more efficient to do this. The below
will first
collapse all with common somefield into a MULTILINESTRING and
then the
LineMerge will do the best it can to stitch back into a single
line string.
This is not possible with completely disjoint linestrings.
SELECT somefield, ST_LineMerge(ST_Collect(the_geom))
FROM sometable
GROUP BY somefield
If you are using the older version of Postgis, you can just
take out the ST_
in the examples I have above.
Hope that helps,
Regina
-----Original Message-----
From: [EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>
[mailto:[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>] On
Behalf Of Bob
Pawley
Sent: Wednesday, April 30, 2008 12:40 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Line To Path
Is there a method of converting three lines that require three
rows into a
path that occupies a single row??
Bob Pawley
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