postgres and postgis

Hello,
I have georeferenced entries in a Postgres table, mostly with the
"point", "box" and "polygon" datatypes. I used then for queries from
self-written CGI scripts which works very well.

However, for extending geographical uses of my data, e.g. with
MapServer, I consider switching to PostGIS, which, on the other hand
supports similar datatypes (following OpenGIS Simple Feature
Specifications) , but not the same ones. The advantage of OpenGIS Simple
Features is that lots of popular GIS applications (such as UMN
MapServer) support them.

a) How arere the postgis geometries related with postgresql objects? Is
there a connection in the development?
b) Has anybody tested migrating data from postgres to PostGIS? Is this
step useful? What is the best practice? Or does somebody have an idea
how to provide the connection?

Thanks,

Regards, Hubert

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Dr.-Ing. Hubert Fröhlich
Bezirksfinanzdirektion München
Alexandrastr. 3, D-80538 München, GERMANY
Tel. :+49 (0)89 / 2190 - 2980
Fax :+49 (0)89 / 2190 - 2459
hubert(dot)froehlich(at)bvv(dot)bayern(dot)de