Re: Postgres native geometry types

On 4 March 2011 22:58, Kasia Tuszynska <ktuszynska(at)esri(dot)com> wrote:

> Hi Everybody,
>
>
>
> I am doing some testing on the postgres native geometry types, namely:
> point, line, lseg, box, path (closed), path [open], polygon and circle.
>
>
>
> Does anyone know what are they being used for? PostGIS is usually
> designated as the gis “module” to postgres and there are other spatial types
> that work on postgres.
>
> So, what are the native geometry types on postgres used for?
> http://www.postgresql.org/docs/9.0/static/datatype-geometric.html#AEN6332
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>
>

Hi,
I think this part of PostGIS documentation describes the difference well
http://postgis.refractions.net/documentation/manual-1.5/ch04.html#PostGIS_GeographyVSGeometry
.

The main idea is that normal geometry types are using standard flat surface
and normal (Euclidean) 3d space.
The postgis types are using some spheroid defined in an appripriate WGS,
this spheroid is similar to Earth shape and has its size in meters, not just
virtual mathematical coordinates.

If you use the normal geometry types, you do it like you'd perform
calculations in math, using some virtual points and distance calculated
using the Pythagorean theorem.
Using postgis, you use points that are defined on some spheroid (depending
on the WGS) and you provide longitude and latitude. The distance between two
geographical points can be calculated in meters and is defined on surface of
the spheroid, not in straight line like in math.

I hope that helps a little.

regards
Szymon