[OSM-talk] TIGER 101

[Ben Gimpert]

Hi Andy,

Yeah, that could work.  Just by my own rule of thumb, 0.0000005 of a
degree worked pretty well for (tiny!) Manhattan.  Though you might have
to incorporate the *cos(lat) term for bigger rural counties.

		Ben


On Thu, 30 Nov 06 @05:33pm, Andy Robinson wrote:
> ok, understood. But can one rough rule be used for urban and another for
> back country? A small import for a few random counties would give an idea of
> the range required.
> 
> Cheers
> 
> Andy
> 
> Andy Robinson
> Andy_J_Robinson at blueyonder.co.uk 
> 
> >-----Original Message-----
> >From: talk-bounces at openstreetmap.org [mailto:talk-
> >bounces at openstreetmap.org] On Behalf Of Ben Gimpert
> >Sent: 30 November 2006 5:26 PM
> >To: talk at openstreetmap.org
> >Subject: Re: [OSM-talk] TIGER 101
> >
> >Hi Andy,
> >
> >As I explained in my previous email, the displacement technique does not
> >scale.  Yes, "one meter" might work for San Francisco but it doesn't for
> >rural Montana.  (This is not conjecture.  I've already written this
> >code, and it doesn't work.)
> >
> >		Ben
> >
> >
> >On Thu, 30 Nov 06 @04:55pm, Andy Robinson wrote:
> >> Ben,
> >>
> >> Thanks for the update. I think the key one to get right is the node
> >reuse.
> >> Grouping individual street ways parts into a single street is less
> >critical
> >> because it's a fairly easy task to do by hand if you need it. It's not
> >> feasible to merge nodes by hand though.
> >>
> >> As you say the data is coarse and therefore its not really a problem to
> >> consider node combination similarly. However if I look at the San
> >Francisco
> >> data I don't see node displacement at junctions exceeding 1 metre (in
> >fact
> >> significantly smaller if not the same lat and lon) so I'm guessing that
> >many
> >> of the street junctions do have the same lat/lon or at least very close
> >to
> >> it. Its very unlikely that there is a problem combining points that are
> >> within that sort of radius anyway.
> >>
> >> Cheers
> >>
> >> Andy
> >>
> >> Andy Robinson
> >> Andy_J_Robinson at blueyonder.co.uk
> >>
> >> >-----Original Message-----
> >> >From: talk-bounces at openstreetmap.org [mailto:talk-
> >> >bounces at openstreetmap.org] On Behalf Of Ben Gimpert
> >> >Sent: 30 November 2006 4:36 PM
> >> >To: talk at openstreetmap.org
> >> >Subject: Re: [OSM-talk] TIGER 101
> >> >
> >> >Hi Andy & Steve,
> >> >
> >> >Right, nodes are not being reused.  This is just because of how they are
> >> >represrented they are represented in the TIGER data itself.  I've posted
> >> >about this before -- how "5th Avenue" in Manhattan is actually N
> >> >separate record chains in TIGER, though obviously it's a
> >> >physically-contiguously street.  And that this occurs also at the node
> >> >level, where there is no level of abstraction in the TIGER dataset for
> >> >shared nodes.
> >> >
> >> >Take a look at:
> >> >
> >> >	http://svn.openstreetmap.org/utils/tiger_import/tiger/tiger.rb
> >> >
> >> >...and note how the TIGER files present (only) raw lat/long, at every
> >> >scale (node, street, point-of-interest).
> >> >
> >> >We have to remember that the TIGER data is just a *very* rough first
> >> >step to a usable streetmap of America.  I'm sure companies like MapQuest
> >> >have had to spend enormous money and/or effort to clean things up for
> >> >their driving directions.
> >> >
> >> >I wrote some code to intelligently try to merge roads with the same
> >> >names that share (roughly) an end node-or-two.  This code didn't scale
> >> >well outside of Manhattan, since FIPS counties can be very strangely
> >> >shaped and sized.  (See Steve's 'blog post on Gerrymandering for a
> >> >similar topic...  Heh.)
> >> >
> >> >As for re-using nodes, we face a similar problem of scaling:  At what
> >> >lat/long precision do we consider two points the "same"?  (Say 0.00005
> >> >of a degree, or what?)  Again, answering this question is hard across
> >> >the entire (HUGE) country.
> >> >
> >> >We might define a formula based upon the smallest rectangle that can
> >> >cover a county.  Say, (maxCountyLongitude - minCountyLongitude) / 10^5,
> >> >but this, umm, doesn't work.  (I tried already.)
> >> >
> >> >Let me know via email if someone else wants to take a crack at writing
> >> >code to "merge nodes" (and streets) in the TIGER data.  I myself won't
> >> >be able to write any more code for OSM since I'm bogged down in other
> >> >responsibilities.  Especially given OSM's wiki nature, I feel like a
> >> >routing system will have to have some intelligence about assuming two
> >> >"nearby" nodes are really the same intersection / bend / whatever.
> >> >
> >> >Hope this make sense!
> >> >
> >> >		Cheers,
> >> >		Ben
> >> >
> >> >
> >> >On Thu, 30 Nov 06 @03:20pm, Andy Robinson wrote:
> >> >> Ben,
> >> >>
> >> >> Looking at the San Francisco data newly imported it still appears that
> >> >ways
> >> >> are being added without connection to adjacent ways, ie there is no
> >> >sharing
> >> >> of common nodes. See JOSM screen dump where I have selected and
> >dragged a
> >> >> way. It should have tugged the adjacent ways too.
> >> >>
> >> >> http://ajr.hopto.org/osm/tiger-nodes.png
> >> >>
> >> >> Cheers
> >> >>
> >> >> Andy
> >> >>
> >> >> Andy Robinson
> >> >> Andy_J_Robinson at blueyonder.co.uk
> >> >>
> >> >> >-----Original Message-----
> >> >> >From: talk-bounces at openstreetmap.org [mailto:talk-
> >> >> >bounces at openstreetmap.org] On Behalf Of Ben Gimpert
> >> >> >Sent: 30 November 2006 2:53 PM
> >> >> >To: talk at openstreetmap.org
> >> >> >Subject: [OSM-talk] TIGER 101
> >> >> >
> >> >> >Hi OSM,
> >> >> >
> >> >> >The TIGER -> OSM import is (again) kicked off and going.
> >> >> >
> >> >> >Since there is now disaster recovery logic atop a MySQL tracking
> >> >> >database, a proper status report is possible.  Unless there are any
> >> >> >objections, I intend to commit the status report to the OSM SVN
> >> >> >repository every night at 3am:
> >> >> >
> >> >> >		http://svn.openstreetmap.org/utils/tiger_import/status
> >> >> >
> >> >> >Dig the tiny-but-increasing numbers for CAlifornia, around our first
> >> >> >prioritized counties (for Mikel).
> >> >> >
> >> >> >		Cheers,
> >> >> >		Ben
> >> >> >
> >> >> >
> >> >> >_______________________________________________
> >> >> >talk mailing list
> >> >> >talk at openstreetmap.org
> >> >> >http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
> >> >>
> >> >
> >> >_______________________________________________
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> >>
> >
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