[postgis-users] PostGIS wrapper for proximity queries

[Brent Wood]

--- Willy-Bas Loos <willybas at gmail.com> wrote:

> We are currently looking for a solution to store (and use, combine)
> information from different original coordinate systems in one table. It
> seems like the best solution to store the geoms in WGS84 and convert it to
> whatever srid the client needs.

Hi,

I use a variety of projections for my data, for several reasons, & have found
PostGIS eminently capable.

For optimum retrieval performance, I have physical tables with a separate
geometry column for each projection. One example is a table of some 1,000,000
polygons, natively in WGS84 lat/long, but also in a separate custom equal area
projection for areal analyses of the polygons. Each column with it's own
spatial index.

Generally, I use a view which generates the additional projected versions on
the fly from the base WGS84 polygons, so that queries on this table do not need
to include the transforms for output data. This approach may well suit your
use.

Occasionally I have used views with transforms from data stored natively in
different projections using union to concatenate the different tables/datasets
without physically merging them into a single table.

Multiple geometries for features is something I think PostGIS does well, much
better than most GIS packages. In addition to different projections for a
feature, I also store startpoints, endpoints, lines, buffered lines/polygons as
physical geometry columns in some tables, having 5 geometries in a table is not
that unusual. Data issues mean I don't always have tracklines, or both start &
finish positions, so need to handle a variety of incomplete spatial data values
pertaining to individual features/rows. 


HTH,

  Brent Wood