[postgis-devel] Common Code

[Mark Cave-Ayland]

On 08/08/11 17:55, Paul Ramsey wrote:

> We actually need two pieces of common code now.
>
> - liblwgeom, which is already there, and Sandro is cleansing, is
> common to geometry, raster, loader dumper, even the documentation
> builder!
> - postgis, which is what we currently call geometry/geography should
> be an agnostic place were we have some utilities for caching call
> information between calls (used by projection, prepared geometries,
> etc) and other code that is common to all types, but has a dependency
> on pgsql. In an "ideal" world, we would have: ?
>
> ./liblwgeom
> ./postgis/common
> ./postgis/geometry
> ./postgis/geography
> ./postgis/raster
> ./postgis/topology
> ./postgis/geocoder
> ./docs
>
> Or something like that. In any event with raster in the pool the need
> for a separated out utility library of pgsql-dependent things goes up.
>
> P.

+0.5 which is nearly a +1 with some caveats ;)

I think the above directory structure is good, but there are a couple of 
extra things I'd like to push into liblwgeom: the projection cache and 
also the geometry 1D R-Tree code.

The reason for doing this is that it makes things much easier to test 
and benchmark outside of PostgreSQL and will also be a bit of value-add 
for people using liblwgeom outside of PostGIS.

Apologies that I haven't had much in the way of time to look at Bryce's 
patches, but I would envisage the liblwgeom projection API to look 
similar to this:

PROJ4Context = lwgeom_proj_context(char *fromproj4text, char *toproj4text);
lwgeom_project(PROJ4Context *ctx,  G_GEOMETRY g);
lwgeom_proj_context_destroy(PROJ4Context *ctx);

We can then handle the caching internally to liblwgeom and then simply 
store the context pointer within the fcinfo->flinfo->fn_extra to keep 
things really simple.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
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