[OSM-dev] TIGER import

[James Marca]

Hi, sorry about the new thread but I just joined the list.

I too am interested in importing TIGER/Line files into OSM.  

Our interest is to generate a proper, navigable network that can be
used for routing, etc.  Consequently we want to get all the
connections between links and nodes correct.

I will focus initially on Orange County, California.

Not to disparage the Ruby-based efforts, but I have zero experience
with Ruby.  I am probably going to tackle the problem orthogonally by
starting with the PostgreSQL/PostGIS database generated by ogr2ogr.  I
set up a small perl script to do that for all California counties,
based on the one used by Geo-Coder-US-1.00/eg/import_tiger_zip.pl, but
using ogr2ogr to do the parsing.  Starting from there, we will work
locally (not yet sure how to do that) to try to get a reasonable
product, and then seek approval for carpet bombing the main OSM
database.

I understand from reading the mailing list archives (March, 2007, I
think) that one problem is that roads that should be connected are not
due to different coordinates of the end points (small errors).  We've
noticed that as well, and have also found a more common case where
road sections connect at nodes, but those nodes shouldn't be mistaken
for intersections (for example, a freeway in cut crossed by a street
at grade).  I am going to experiment with correcting the first problem
using PostGIS functions, and correct the second by heuristics (roads
don't intersect with freeways without intervening ramps, etc).

One final point, my colleague has developed an A-Star-based map
matching algorithm that does a reasonably good job at matching GPS
traces with the correct TIGER/Line segments.  Since those segments
can be pretty coarse, I think that might offer one way to improve the
alignment of the road centerlines.

I don't want to spam this list, so I may just create another page on
the Wiki linked to the main TIGER page for our effort, and use it as a
place to document our progress, process, and tricks.

Cheers, and thanks to all for this tool so far.  I hope we can
contribute in kind.

James