[postgis-users] rookie question: how to extract latitude and longitude values from geography(POINT) column?

[David Fawcett]

Apologies for the bad direction.  I did find a list of functions that
apply to geography types:
http://postgis.refractions.net/documentation/manual-1.5SVN/ch08.html#PostGIS_GeographyFunctions

On Wed, Jan 5, 2011 at 10:30 AM, W. Matthew Wilson <matt at tplus1.com> wrote:
> On Wed, Jan 5, 2011 at 10:09 AM, David Fawcett <david.fawcett at gmail.com> wrote:
>> I haven't tried them specifically with the geography type, but I would
>> assume that ST_AsText(), ST_X(), and ST_Y() should work.
>>
>> Something like:
>>
>> SELECT ST_X(myGeogColName), ST_Y(myGeogColName)
>>   FROM myTable;
>
> Apparently ST_X wants a geometry point, not a geography point.  I
> tried this and it failed:
>
> dev=> select ST_X(ST_GeogFromText('POINT(11 12)'));
> ERROR:  function st_x(geography) does not exist
> LINE 1: select ST_X(ST_GeogFromText('POINT(11 12)'));
>               ^
> HINT:  No function matches the given name and argument types. You
> might need to add explicit type casts.
>
> So then I converted the geography point into a geometry point, and it works OK:
>
> dev=> select ST_X(ST_GeomFromText(ST_AsText(ST_GeogFromText('POINT(11 12)'))));
> +------+
> | st_x |
> +------+
> |   11 |
> +------+
> (1 row)
>
> What is the right way to convert a geography point to a geometry
> point?  Is there something better / faster / safer than dumping to
> text and then reloading?
>
> Thanks for the help.
>
> Matt
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