[Talk-ca] Fwd: Merging OSM + Geobase

[James Ewen]

Can we change the reply rules on this reflector so it can be used
easily for reflector discussions, instead of defaulting to
off-reflector replies?

On Fri, Mar 27, 2009 at 7:25 AM, William Lachance <wrlach at gmail.com> wrote:

> It probably depends on region. I find the geobase data around Halifax to
> be remarkably accurate. If that isn't the case for other parts of
> Canada, we could easily add a flag to a merging tool to favour the
> positioning/naming of the existing user-contributed OSM data if that
> were preferable.

We are already doing that... the scripts being used ignore GeoBase
data in favour of existing OSM data.


> Right, so what I'm proposing here is that we don't skip the existing
> roads, but merge them. In the case of the HRM, I'd propose simply
> replacing the existing positioning data with the geobase information,
> which should solve the issue of stitching roads together.

That was decided against before the import experiment began. How would
you propose merging the two ways? We went over this previously, and
the consensus was to leave OSM data in place, and only import the
GeoBase data where there was no existing data. The problem is that you
either use the OSM nodes and ways, the GeoBase nodes and ways, or some
hybrid of the two. If you are going to create a hybrid, then there's a
whole new set of decisions to be made.

> Maybe I'm not understanding something, but why couldn't you just add a
> new node to both ways at the point of intersection? I don't see why that
> would look like a mini off ramp -- on the contrary, it wouldn't change
> the actual geometry of either way at all!

Well, you wouldn't want or need to add two nodes at the exact same
spot. Just add a single node and connect the two ways to that node. As
to your second statement, have you actually looked at the same images
of Camrose yet? Some of the ways stop short of the OSM ways. It would
be simple to add a segment between the end of the Geobase way, and the
existing OSM way. However some of the GeoBase ways extend across the
OSM way. By connecting the end of the GeoBase way to the OSM way, you
will be backtracking on the GeoBase way. The map representation would
show that the GeoBase road crosses over the OSM road, and then doubles
back on itself before you get to the intersection.

Smarter stitching routines need to be created. There are also times
where the duplicate detection doesn't work perfectly. In Sherwood
Park, there are a number of cul-de-sacs where the OSM loop at the end
of the road has been duplicated by the GeoBase loop, simply because
the script rules don't match the ways properly. Writing rules that
approach the ability of the human mind to determine which ways match
in the two databases is a difficult proposition.

In areas of low OSM data density, we gain the most positive input, but
in areas of high OSM data density, we run the risk of creating more
issues than unique data imports.

James
VE6SRV