[postgis-users] Geography Data Type vs. Geometry Data Type w/ SRID of 4326?

[Richard Gomes]

I run into this difficulty too.. or kind of similar issue.

In a nutshell, I'm using EclipseLink and it does not recognized 
Geography data type because there's no Geography class in postgis-jdbc 
package.

Actually, in my specific situation, I realized that I don't need 
Geography data type and I don't need even Geometry data type at all on 
the client side. At the moment, I've created column names such as 
longitude, latitude, northing, easting, geography and geometry that 
allows me perform any query I need on the database side. I've also 
created indexes on geography and geometry columns at the moment.

If I need to do something like opening Google maps, for example, all I 
need to do is transfer longitude and latitude to the client side. So, 
again, this is highly unlikely that I need to transfer geography or even 
geometry fields to the client side.

Actually, at the moment, I'm only using Geometry data type (only Points) 
and a Box2D which is intended to limit the domain of Points which should 
be considered in a given query. See more on this: 
http://postgis.refractions.net/docs/ch04.html#id2638955

This is an example of a native query I perform on the database side:

select a.postcode from postcode a, location b
where
          b.fips = 'UK' and b.location like 'British Museum, %'
   and a.geometry && st_expand(b.geometry, 1000)
   and st_distance(a.geometry, b.geometry) <= 200;

There are ~1.7 million postcodes and ~250,000 locations in the database.
This query executes in about 40ms, which is pretty decent.

Regarding SRID, it depends on your application, accuracy you need, etc.
In my specific case, I only perform local queries, up to 50 miles. So, I 
decided by storing Points matching the official SRID for a given 
country. In the case of UK, I'm using this: 
http://spatialreference.org/ref/epsg/7405/
I had to first do this: http://spatialreference.org/ref/epsg/7405/postgis/

I hope it helps

Richard Gomes

On 05/04/11 15:42, maw269 wrote:
> I noticed that GeoServer 2.0.3 does not recognize (yet) Geography Data Types.
> What would happen if you stored a lat/lon pair in a Geometry Data Type and
> gave it an SRID of EPSG:4326? Is that even possible? Would that break the ST
> functions available for Geometries?
> Matt
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