[postgis-users] Transforming Coordinates

Obe, Regina robe.dnd at cityofboston.gov
Wed Jul 18 13:38:29 PDT 2007

Not quite sure what you are asking.  For this kind of stuff, I usually
create a view and use that for google maps if I have a lot of apps that
need it or you could alternatively just write the sql of the view each
time you need it. 
Would be something like this
CREATE VIEW vwbusstopsgoogle As
    select x(transform(east_north, 4326)) As lon,
y(transform(east_north,4326)) As lat, [other fields you need go here]
        FROM bus_stops1
The to use
SELECT lon, lat from vwbusstopsgoogle
To transform back it would be
INSERT INTO bus_stops1(east_north)
    values(transform(setsrid(makepoint([lon],[lat]), 4326), 27700))
WHERE [lon], [lat] you replace with the x y you get from google.


From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Alan
Sent: Wednesday, July 18, 2007 4:28 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Transforming Coordinates

Hi guys

I have a table with easting northing coordinates and these points in a
geom column. I have 15,000 points with an easting and a northing
(brittish national grid) and created the geom column using these

SELECT AddGeometryColumn( 'bus_stops1', 'east_north', 27700, 'POINT', 2
UPDATE bus_stops1 SET east_north = PointFromText('POINT(' || easting ||
' ' || northing || ')',27700);

The table looks like this at the moment:

 easting | northing |                     east_north
  226965 |   676038 | 0101000020346C000000000000A8B40B41000000008CA12441
  226761 |   675945 | 0101000020346C00000000000048AE0B4100000000D2A02441
  226696 |   675893 | 0101000020346C00000000000040AC0B41000000006AA02441
  226473 |   675777 | 0101000020346C00000000000048A50B4100000000829F2441
  226465 |   675731 | 0101000020346C00000000000008A50B4100000000269F2441
  226614 |   675611 | 0101000020346C000000000000B0A90B4100000000369E2441
  226603 |   675605 | 0101000020346C00000000000058A90B41000000002A9E2441
  226869 |   675621 | 0101000020346C000000000000A8B10B41000000004A9E2441
  226883 |   675630 | 0101000020346C00000000000018B20B41000000005C9E2441
  226544 |   674911 | 0101000020346C00000000000080A70B4100000000BE982441
  226767 |   675293 | 0101000020346C00000000000078AE0B4100000000BA9B2441
  226767 |   675303 | 0101000020346C00000000000078AE0B4100000000CE9B2441

Now what I want to be able to do is to add another column or two columns
with X and Y values in WGS or the standard X and Y coordinates for entry
into google maps. I dont want to transform the east_north column so that
I get another long string as is shown above as I cannot then integrate
them into google maps. Can this be done using PostgreSQL?

Also I would like to do the opposite too. Take x and y coordinates from
google maps and transform them to easting northing as above. Thanks for
your help again


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