[Talk-ca] Merging OSM + Geobase

[James Ewen]

On Thu, Mar 26, 2009 at 1:00 PM, William Lachance <wrlach at gmail.com> wrote:

> I've been following the discussions about the geobase import with
> interest. There seems to be some concern about how to correlate the
> existing OSM data with the Geobase dataset. In particular, how do we get
> the superior positioning and connectivity of geobase without blowing
> away all the great work people have done tagging their manually inputted
> ways?

I keep seeing people talk about the superior positional accuracy of
the GeoBase data. From the sections that I have interacted with, I
would find it hard to support this statement. The position accuracy of
the GeoBase data that I have dealt with is very easily recognized as
much less than the OSM data.

However, the sheer volume of GeoBase data makes the database of
interest. I have higher accuracy, or at least better representational
data in the OSM database in areas where I have been working, but I am
still interested in blowing away all of the data that I have entered
in favour of importing the full GeoBase data set. From there I will
once again go over the GeoBase data, and fill in the extra data
required to bring the GeoBase data up to the OSM data representation
level.

This is worthwhile in my opinion due to the ability to have large
amounts of lesser quality data in areas where there is currently no
data at all.

> One alternative which I haven't heard mentioned is the possibility of
> _merging_ the two datasets.

That's what is happening now, using a script that watches for existing
roads, and skipping them. The issue is stitching the newly imported
roads to existing roads.

The problem appears to me to be the fact that the existing ways will
need to have nodes added to them for the imported ways to link to. The
software being used right now does not do that, but rather just stops
the import at the next closest node on the imported way. There will
need to be some type of decision making process happen in the import
scripts that either a) finds a node on the existing OSM way that is
within a specified distance from where the imported node should be, or
b) create a new node on the existing way, and connect the imported way
to the newly created node on the existing OSM way.

This would solve the issue of having the two road databases being
separate, but it would still require manual intervention to fix the
inevitable problems.  If you look at the example from Camrose, you
will see that some GeoBase roads stop short of the OSM way, while
others cross the OSM way. If a new node was added and connected to the
node that crosses the OSM, it will look like there's a mini off ramp
or something.

James
VE6SRV