Re: Which function transform x,y to latitude/longitude?

On Wed, Apr 25, 2007 at 05:02:02PM +0800, Nemo Terry wrote:
> For example x= 38356.62 y= 42365.19.how to transform it to latitude
> 1.399948, longitude 193.92644?

Do you mean longitude 103.92644? In what datum are the lat/lon
coordinates? Where did you get the transformation in your example?

> Which function I could use? I don’t know the algorithm.
>
> Initial data is: ("+proj=cass +a=6378137.0 +rf=298.257223563
> +lat_0=1.287639n +lon_0=103.8516e +x_0=30000 +y_0=30000").

What's the source of these parameters?

You can perform transformations outside the database with PROJ.4
or inside the database with the PostGIS transform() function (which
uses PROJ.4).

http://proj.maptools.org/
http://postgis.refractions.net/

I don't see any exact matches in the PostGIS spatial_ref_sys table
for the parameters you posted you so if you use PostGIS then you
might have to insert a row to create your own spatial reference
system. However, I did a few tests with your parameters and various
datums for the lat/lon and couldn't get the exact transformed values
in your example.

You might get more help on the PROJ.4 and PostGIS mailing lists.

--
Michael Fuhr