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Today's Topics:
1. Why Multiply? Why not? ( Mohamad Solikin (via Multiply) )
2. RE: Which postGIS functions to use? (Paragon Corporation)
3. Re: Which postGIS functions to use? (Stephen Woodbridge)
4. PostGIS functions inside triggers (Eduin Yezid Carrillo Vega)
----------------------------------------------------------------------
Message: 1
Date: Sun, 15 Feb 2009 1:43:34 -0500
From: " Mohamad Solikin (via Multiply) " <[email protected]>
Subject: [postgis-users] Why Multiply? Why not?
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Check out my Multiply site
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to add you as my friend so you can see it. First, you need to join
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Thanks,
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------------------------------
Message: 2
Date: Sun, 15 Feb 2009 05:39:28 -0500
From: "Paragon Corporation" <[email protected]>
Subject: RE: [postgis-users] Which postGIS functions to use?
To: "'PostGIS Users Discussion'"
<[email protected]>
Message-ID: <f96d34a9696b465f9fe7d73585115...@b>
Content-Type: text/plain; charset="us-ascii"
I don't quite understand your question.
Are you trying to get the length of the intersection of the 2? So that part
of the network component that falls within the quay?
In that case it would be something of the form
SELECT ST_Length(ST_Intersection(netcomponent.the_geom, quay.the_geom))
Which assumes your netcomponent is defined as a LINESTRING (you can use
ST_MakeLine
http://postgis.refractions.net/documentation/manual-svn/ST_MakeLine.html
if you have 2 points and no line)
And quay is some sort of polygon.
Hope that helps,
Regina
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Saturday, February 14, 2009 11:31 AM
To: [email protected]
Cc: [email protected]
Subject: [postgis-users] Which postGIS functions to use?
I have a "network component" (= part of a waterway) defined by 2
coordinates.
I know how to calculate the length of that component.
However, another component, let's say a quay, overlaps with the component. I
know how far it overlaps (in meters) with the component from the beginning
coordinate and I want to calculate the end coordinate of the quay (that
should be on the network component).
How do I do this?
Thank you
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postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
------------------------------
Message: 3
Date: Sun, 15 Feb 2009 11:15:40 -0500
From: Stephen Woodbridge <[email protected]>
Subject: Re: [postgis-users] Which postGIS functions to use?
To: PostGIS Users Discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I'm not sure if I understand you question correctly, but here is a
solution for my understanding.
So you have a network component that is partially overlapped by the quay
and you know the length along the network component where the overlap
starts or stops. You can extract the part of the network component that
overlap with ST_Intersection or ST_Difference as Regina suggests. You
can also do this using the linear referencing functions which might be
faster:
From start of netcomponent to your distance of intersection:
SELECT ST_line_substring(netcomponent.the_geom, 0.0,
dist_meters/ST_length_spheroid(netcomponent.the_geom,spheroid))
From your distance of intersection to the end of the netcomponent:
SELECT ST_line_substring(netcomponent.the_geom,
dist_meters/ST_length_spheroid(netcomponent.the_geom,spheroid), 1.0)
If you just want the point of intersection with the quay then this
should do it:
SELECT ST_locate_along_measure(netcomponent.the_geom,
dist_meters/ST_length_spheroid(netcomponent.the_geom,spheroid))
All these functions assume your geometry is in units degrees and you
will need to define an appropriate value for spheroid like:
SPHEROID[<NAME>,<SEMI-MAJOR AXIS>,<INVERSE FLATTENING>]
for example:
'SPHEROID["GRS_1980",6378137,298.257222101]'
-Steve
Paragon Corporation wrote:
I don't quite understand your question.
Are you trying to get the length of the intersection of the 2? So that part
of the network component that falls within the quay?
In that case it would be something of the form
SELECT ST_Length(ST_Intersection(netcomponent.the_geom, quay.the_geom))
Which assumes your netcomponent is defined as a LINESTRING (you can use
ST_MakeLine
http://postgis.refractions.net/documentation/manual-svn/ST_MakeLine.html
if you have 2 points and no line)
And quay is some sort of polygon.
Hope that helps,
Regina
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Saturday, February 14, 2009 11:31 AM
To: [email protected]
Cc: [email protected]
Subject: [postgis-users] Which postGIS functions to use?
I have a "network component" (= part of a waterway) defined by 2
coordinates.
I know how to calculate the length of that component.
However, another component, let's say a quay, overlaps with the component. I
know how far it overlaps (in meters) with the component from the beginning
coordinate and I want to calculate the end coordinate of the quay (that
should be on the network component).
How do I do this?
Thank you
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
------------------------------
Message: 4
Date: Sun, 15 Feb 2009 12:16:26 -0500
From: Eduin Yezid Carrillo Vega <[email protected]>
Subject: [postgis-users] PostGIS functions inside triggers
To: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
Maybe I miss something, but ST_Contains isn't available inside this
trigger. It returns empty values trying to get which polygon in table2
contains a recently inserted point on table1. table1.the_geom value is
filled correctly but table1.table2_id value is null. Tried ST_Within
and ST_Intersects also.
CREATE TABLE table1
(
table1_id serial NOT NULL,
lon character varying(30),
lat character varying(30),
table2_id character varying(200),
the_geom geometry,
CONSTRAINT table1_pkey PRIMARY KEY (table1_id),
CONSTRAINT enforce_dims_the_geom CHECK (ndims(the_geom) = 2),
CONSTRAINT enforce_geotype_the_geom CHECK (geometrytype(the_geom) =
'POINT'::text OR the_geom IS NULL),
CONSTRAINT enforce_srid_the_geom CHECK (srid(the_geom) = 4326)
)
WITH (OIDS=FALSE);
CREATE TRIGGER table1_change
AFTER INSERT OR UPDATE OR DELETE
ON table1
FOR EACH ROW
EXECUTE PROCEDURE table1_change();
CREATE TABLE table2
(
gid serial NOT NULL,
table2_id character varying,
the_geom geometry,
CONSTRAINT table1_pkey PRIMARY KEY (table2_id),
CONSTRAINT enforce_dims_the_geom CHECK (ndims(the_geom) = 2),
CONSTRAINT enforce_geotype_the_geom CHECK (geometrytype(the_geom) =
'MULTIPOLYGON'::text OR the_geom IS NULL),
CONSTRAINT enforce_srid_the_geom CHECK (srid(the_geom) = 4326)
)
WITH (OIDS=FALSE);
CREATE OR REPLACE FUNCTION table1_change()
RETURNS trigger AS
$BODY$
DECLARE
the_point geometry;
a_row table2%ROWTYPE;
BEGIN
IF tg_op = 'INSERT' THEN
SELECT ST_GeomFromText('POINT(' || new.lat || ' ' || new.lon ||
')',4326) INTO the_point;
SELECT * FROM table2 WHERE ST_Contains(table2.the_geom,
the_point) INTO a_row;
UPDATE table1 SET
table2_id = a_row.table2_id,
the_geom = the_point
WHERE table1_id=new.table1_id;
END IF;
RETURN new;
END
$BODY$
LANGUAGE 'plpgsql' VOLATILE
COST 100;
ALTER FUNCTION table1_change() OWNER TO postgres;
Triggered with:
INSERT INTO table1(table1_id, lon, lat) VALUES
(999,-73.138583333333,7.0854783333333);
Eduin Yesid Carrillo Vega
Ingeniero Civil, Esp. Sistemas de Información Geográfica
Bogotá D.C., Colombia
------------------------------
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