[Talk-ca] OSM Geobase import: giving a try

Frank Steggink steggink at steggink.org
Sun Feb 15 23:05:48 GMT 2009


Hi Steve,

Thanks for your response.

> Yes the wiki needs a cleanup, I've been hoping someone else would do it 
> since that doesn't seem to be happening I will try to find sometime soon 
> to delete all obsolete information from the wiki pages.
I'll try to do some cleanup, once I have a better understanding of th eefforts 
of others.

> Yes please try to keep nids for data that actually comes from geobase.
> Not importing could limit us in the future.
In what way would it limit us? When we'll receive a new dataset from Geobase? Or 
do you hint towards other datasets which are linked to the NID? In that case 
that additional data can't be linked to existing database, because that doesn't 
contain the NID attributes.

>>     b. How can we guarantee that the final import will be consistent? 
>> (See also
>> my first question.)
> 
> Depends what you mean by consitent.
> 1. Using consistent tags for things, the best way to ensure this is to 
> look at what others are doing and share your scripts.
> 
> 2. data consistency, ie roads line up and are joined between different 
> imports or between the existing and geobase data.  Right now we have no 
> automated consistency tools, we are depending on people to manually line 
> up/connect ways post import.
Both meanings were intended. I wonder if automatic consistency will work. It 
seems to have a too high chance of failure.

> You are free to use your own processes and software.  I don't think any 
> two people are doing the exact same thing for importing.  This is the 
> process I follow
> 
> You don't need to use roadmatcher, you just need to have some method of 
> avoiding hundreds of duplicate roads.
I actually wanted to use PostgreSQL/PostGIS, but it seems that no OSM data can 
be exported from it. At least not when OSM data was previously imported through 
osm2pgsql. Maybe it will work to keep the Geobase data in Postgis, export as 
OSM, and then apply some postprocessing (fixing in JOSM).

> For comparision purposes what I've done with the larger areas in Alberta:
> 
> 1. Populate a postgis database with the NRN shapefile
> 2. Populate a postgis database with the OSM data using osm2pgsql
> 3. Generate a NRN and OSM shapefile for the area that I'm interested in
> using pgsql2shp and some SQL queries. I handle reprojection during this
> process as well (lately I've been reprojecting into meters)
> 4. Import both shapefiles into jump and automatch with roadmatcher
> 5. Export my results
> 6. Run geobase2osm on the NRN GML file(yes I had to download the NRN data
> twice) and produce a standalone file
> 7. Review the standalone file in JOSM
> 8. Upload the standalone file with bulk_upload.pl
> 9. Manual fixup in JOSM.
I'm going to try to generate buffers around the imported road data from OSM, and 
will use it to clip away any Geobase data (NRN) which is entirely within a 
certain distance from the OSM data. And then export it to OSM. I'll need to work 
it out further, using my test area. I think that a buffer of 10 or 20 meter is 
enough.

> Do not use any of the Ibycus stuff the import the licenses are not 
> compatible. Do not use ibycus in the geobase import.  Someone should 
> have removed these references from the wiki a long time ago.  I will try 
> to do it soon.
OK. Makes sense to me. It's already postprocessed to some degree, rendering it 
less suitable.

> I just viewed/posted my initial .osm files in JOSM and when people where 
> happy with them I did an import to a small isolated area.  Using a 
> seperate userid is a good idea.
> 
> You can get the latest version of geobase2osm.py here, a number of 
> people have used this as the basis for their custom procedures.
> 
> http://svn.openstreetmap.org/applications/utils/import/geobase2osm/geobase2osm.py 
OK, will give that a try :) But it might be necessary if I use PostGIS as the 
main repository for the Geobase data. I want to remove the number of steps as 
much as possible, to make it more automatable and user friendly.

One final question: what is the accuracy of the Geobase data? Is it worse, 
comparable, or better than typical GPS tracks? The roads I've drawn so far match 
the Yahoo imagery quite well, although usually there is a slight offset of a few 
meters.

Regards,

Frank




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