[postgis-users] Converting UTM to lat/lon using Postgis

Mon May 3 00:50:27 PDT 2010

Thank you for the fast answer!

Hmm. It looks I don't have srid 3997 in the DB.

=# select srid, srtext, proj4text from spatial_ref_sys where srid=3997;

 srid | srtext | proj4text

------+--------+-----------

(0 rows)

select srid, srtext, proj4text from spatial_ref_sys where  srtext like
'%Dubai%';

 srid | srtext | proj4text

------+--------+-----------

(0 rows)

Could this be related to my postgis installation? 

I don't see this srid in spatial_ref_sys.sql which came with postgis
installation either. 

Any idea how I can fix this?

-------------------------------------------------------------------

Mehmet ERKEK

www.REIDIN.com <http://www.reidin.com/> 

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Francis Markham
Sent: Monday, May 03, 2010 11:09 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Converting UTM to lat/lon using Postgis

Hi Mehmet,

When you imported the shapefile, the SRID you are meant to specify is
the SRID of the data, not the SRID you want.  Since the data is in Dubai
Local TM, the SRID is 3997.  To get the transformation you want, try the
following:

select   ST_AsText( ST_Transform(centroid(ST_SetSRID(the_geom,
3997)),4326)) from ult.test2 limit 5;

Hope that helps,

-Francis

On 3 May 2010 17:03, Mehmet Erkek <merkek at reidin.com> wrote:

Hi All,

I havea a shape file which I imported it to a table called 'test2'
(using  SRID=4326).  I want to get centroids of geometries in lat/lon. 

Here is what I run:

select   ST_AsText( ST_Transform(centroid(the_geom),4326)) from
ult.test2 limit 5;

and what I get:

POINT(496597.996430787 2774798.21242881)

POINT(496332.629887436 2793339.61534586)

POINT(496302.627327975 2793317.82477318)

POINT(496305.255261594 2793353.29646291)

POINT(496241.538851096 2774826.65593589)

So far all is fine except coordinates which are not  latitude/longitude 

My question is : How can I convert/get these coordinates in lat/lon?

This what I have in my prj file: 

PROJCS["Dubai Local Transverse Mercator
(DLTM)",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",637
8137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.017453292
5199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",50
0000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",55.
33333333333334],PARAMETER["Scale_Factor",1.0],PARAMETER["Latitude_Of_Ori
gin",0.0],UNIT["Meter",1.0]]

And this is my postgis version: POSTGIS="1.3.6" GEOS="2.2.3-CAPI-1.1.1"
PROJ="Rel. 4.7.1, 23 September 2009" USE_STATS

I appreciate any help. Thank you.

-------------------------------------------------------------------

Mehmet ERKEK

www.REIDIN.com <http://www.reidin.com/> 

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