[postgis-users] Transforming Coordinates

[Alan Cunnane]

What I need to do is create a new column in the bus_stops1 table with x and x coordinates. If I use your suggestion below to transform the column east_north to x and y wont both the new X and Y columns be the same value as it is the same query?


----- Original Message ----
From: "Obe, Regina" <robe.dnd at cityofboston.gov>
To: PostGIS Users Discussion <postgis-users at postgis.refractions.net>
Sent: Wednesday, 18 July, 2007 9:38:29 PM
Subject: RE: [postgis-users] Transforming Coordinates





 

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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 

Cunnane
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 

commands:

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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