Re: [osmosis-dev] postGIS: bbox columns?
David, David Carmean wrote: > Thanks for the clarification. Indeed the linestrings are the primary > desired feature in my use cases (as will be polygons constructed from > the closed ways). It is easy to make polygons from closed ways, but quite hard to make polygons from multipolygon relations (at least it's not something that you can do well with a simple st_buildarea). Depending on what exactly you want, you may want to look into the file we're offering (weekly update) at http://download.geofabrik.de/polygon/, it is a PostGIS dump with multipolygon geometries for every single closed way *and* multipolygon relation in OSM. Bye Frederik -- Frederik Ramm ## eMail frede...@remote.org ## N49°00'09" E008°23'33" ___ osmosis-dev mailing list osmosis-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/osmosis-dev
Re: [osmosis-dev] postGIS: bbox columns?
On Sun, May 23, 2010 at 02:31:13AM +0200, Frederik Ramm wrote: > David, [snip] > HOWEVER, it takes much longer to import the full linestrings than to > just import a bbox in the first place. > > So if your application, for whatever reason, does not need pre-built > geometries, but just an overall idea of where in the world a certain way > is, then the bbox builder mechanism in Osmosis allows you to skip > linestring generation altogether, saving time and storage space. [snip] Frederik, Thanks for the clarification. Indeed the linestrings are the primary desired feature in my use cases (as will be polygons constructed from the closed ways). Thanks. ___ osmosis-dev mailing list osmosis-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/osmosis-dev
Re: [osmosis-dev] postGIS: bbox columns?
David, David Carmean wrote: > As described above, this index can be used to perform a quick first-pass > query based on just the table indices (proxy bounding boxes) and present > the main query with a pre-filtered set of candidates. I probably have not made myself clear enough. It is obvious that having a proper linestring in your table, together with a GIST index, beats having just a bbox, and it is unlikely that any application will be unable to make use of the index. HOWEVER, it takes much longer to import the full linestrings than to just import a bbox in the first place. So if your application, for whatever reason, does not need pre-built geometries, but just an overall idea of where in the world a certain way is, then the bbox builder mechanism in Osmosis allows you to skip linestring generation altogether, saving time and storage space. The bbox column does not present added value if you intend to import the full linestrings. It is only useful if you want a lean database without full linestrings. Bye Frederik -- Frederik Ramm ## eMail frede...@remote.org ## N49°00'09" E008°23'33" ___ osmosis-dev mailing list osmosis-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/osmosis-dev
Re: [osmosis-dev] postGIS: bbox columns?
On Sun, May 23, 2010 at 12:23:27AM +0200, Frederik Ramm wrote: > Hi, > > David Carmean wrote: > > Who/what uses the ways.bbox column? Is there something/somebody > > that cannot use the linestring gist index, but instead requires > > an explicit bounding box geometry? > > Is the bbox column not meant to be a quicker alternative to a full > linestring (quicker in importing, not quicker in using)? I.e. you won't > have a linestring to base your GIST index on if you use that as intended. The presence of the gist index on the linestring geometry column is what allows the GIS client I use to link only a small portion of the dataset based on a bounding box I specify; without it, it links the entire table as a drawing layer. The gist index presents a "proxy" bounding box internally. http://postgis.refractions.net/documentation/manual-1.3/ch03.html#id2570609 As described above, this index can be used to perform a quick first-pass query based on just the table indices (proxy bounding boxes) and present the main query with a pre-filtered set of candidates. I'm just wondering if there's some other application that uses this explicitly-built bbox geometry column (and whether it could be improved by using the index instead). ___ osmosis-dev mailing list osmosis-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/osmosis-dev
Re: [osmosis-dev] postGIS: bbox columns?
Hi, David Carmean wrote: > Who/what uses the ways.bbox column? Is there something/somebody > that cannot use the linestring gist index, but instead requires > an explicit bounding box geometry? Is the bbox column not meant to be a quicker alternative to a full linestring (quicker in importing, not quicker in using)? I.e. you won't have a linestring to base your GIST index on if you use that as intended. Bye Frederik -- Frederik Ramm ## eMail frede...@remote.org ## N49°00'09" E008°23'33" ___ osmosis-dev mailing list osmosis-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/osmosis-dev
[osmosis-dev] postGIS: bbox columns?
Who is knowledgable about the osm/postGIS simple schema design and associated scripts? I have several questions, and keep coming up with others, as I experiment with using osm data as GIS base data, but today's question is: Who/what uses the ways.bbox column? Is there something/somebody that cannot use the linestring gist index, but instead requires an explicit bounding box geometry? For what it's worth, I reversed the order and created the linestring geometry column first, and found that creating the bbox column from the linestring instead was seemingly thousands of times faster than creating it (the bbox) from the nodes table. Once I fix a hardware problem I plan to get some hard numbers. Thanks. ___ osmosis-dev mailing list osmosis-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/osmosis-dev
