[OSM-dev] Using NULL values in mapnik / postgres DB

[Artem Pavlenko]

Thanks, I'll try new osm2pgsql/osm.xml tomorrow.
Artem
On Wednesday 21 February 2007 23:19, Jon Burgess wrote:
> See below...
>
> On Tue, 2007-02-20 at 22:12 +0000, Artem Pavlenko wrote:
> > Jon,
> >
> > Sounds good to me! Also, it might be a good idea to split osm data into
> > multiple tables in postgresql and only keep fields that are required :
> >
> > 1. roads (LINESTRING) :  osm_id,highway,level,name ...
> > 2. all points (POINT) : osm_id, amenity,...
> > 3. all polygons (POLYGONS): osm_id, natural, leisure etc.
> >
> > Thoughts?
> >
> > Also, I'm not entirely convinced that using TEXT is more efficient than
> > VARCHAR(<length>) ???  Was it mentioned somewhere in docs?
> >
> > And last one:) . How about correcting geometries at the translation
> > stage? I think we can use GEOS (c++ lib) to 'node' and 'linemerge' _bad_
> > ways into clean ones.
> >
> > Artem
> >
> > On Tuesday 20 February 2007 21:40, Jon Burgess wrote:
> > > I received an email from Martin Spott which suggested that we change
> > > the Postgres database fields used by osm2pgsql + mapnik to utilise NULL
> > > in place of empty text strings.
> > >
> > > Martin believes this will make the database lookups more efficient and
> > > i'm inclined to believe him.
> > >
> > > To make this change we need to change both osm2pgsql.c and the osm.xml
> > > mapnik rules to generate and parse the NULL SQL values.
> > >
> > > I've done a quick trial on my local machine and it is fairly trivial to
> > > implement this. For reference the osm.xml changes look like:
> > >
> > >   char_length(foo)=0   changes to   foo IS NULL
> > >   char_length(foo)>0   changes to   foo IS NOT NULL
> > >
> > > Any thoughts about whether I should go ahead and make this change?
> > >
> > > Jon
>
> I've just commited the relevant changes to use NULLs in place of empty
> strings into both mapnik/osm.xml and osm2pgsql/osm2pgsql.c
>
> The two new versions need to go together else you will get lots of
> unrendered stuff in your map.
>
> If you have a custom osm.xml file which you want to update to this new
> style then running your file through the attached script should convert
> the relevant pieces of SQL for you:
>
> ./nullify my-osm.xml > new-osm.xml
>
> 	Jon