[OSM-dev] Topologicial correctness in OSM

Andy Robinson Andy_J_Robinson at blueyonder.co.uk
Wed Jan 17 19:59:02 GMT 2007


Nick Black [mailto:nickblack1 at gmail.com] wrote:
>Sent: 17 January 2007 7:33 PM
>To: Andy Robinson
>Cc: dev at openstreetmap.org
>Subject: Re: [OSM-dev] Topologicial correctness in OSM
>
>I know that shapefiles store topology, but I dont know much about the
>details of it.
>
>http://www.esri.com/news/arcuser/0401/topo.html
>
>The whole layers thing is a bit odd - working with OSM data, I think
>of layers as an abstraction.  When "mainstream GIS people" talk about
>data, its more lije the attributes are an abstraction of the layer.
>I'm loathed to start another format war, but OSM's model has a lot
>going for it - and has considerably more documentation than Mapinfo's
>format!

I like the OSM format too. My background has previously been CAD and
whenever I've tried to do something like a simple map I've generally been
frustrated. Clearly the GIS related extensions from the CAD developers move
way beyond the basics of CAD but as a simple model OSM seems to fit our
needs so much more simply... even I can understand it :-)

Cheers

Andy


>
>On 1/17/07, Andy Robinson <Andy_J_Robinson at blueyonder.co.uk> wrote:
>>
>> Nick Black wrote:
>> >Sent: 17 January 2007 6:59 PM
>> >To: Jon Burgess
>> >Cc: dev at openstreetmap.org
>> >Subject: Re: [OSM-dev] Topologicial correctness in OSM
>> >
>> >Hurray  I was just about to start writing a script to do it.  I've
>> >said it before, utils/ is a goldmine.  Can you believe that Mapnifo
>> >TABs do not support topology?  I had naively assumed they would. +1
>> >for OSM
>> >
>>
>> I'd be really interested to know (for my own education more than anything
>> else) how many generic systems and formats for geodata treat it like CAD
>(ie
>> layers of lines with no physical connection between the layers) and how
>many
>> are more like OSM where any concept of layers is applied as attributes to
>> the data itself.
>>
>> Answers direct to me if you prefer not to clog the list.
>>
>> Cheers
>>
>> Andy
>>
>> >
>> >On 1/17/07, Jon Burgess <jburgess777 at googlemail.com> wrote:
>> >> On Wed, 2007-01-17 at 17:19 +0000, Nick Black wrote:
>> >> > Hello,
>> >> >
>> >> > Whilst trying to produce .osm from the brazillian TABs, I've run
>into
>> >> > a problem, in that the output I can produce output in OSM XML, but
>it
>> >> > is topologically incorrect, as it duplicates nodes at intersections.
>> >> > My process is:
>> >> >
>> >> > TAB > Import to PostGIS usign ogr2ogr > Script to talk to PG, and
>> >> > input data to OSM MYSQL via dao.rb .
>> >> >
>> >> > One solution to the problem is to go through mysql and compare each
>> >> > lat and lon value to each other, identifying the duplicate nodes and
>> >> > then deleting one set and correcting their parent segment - this
>seems
>> >> > a rediculous way to do it though.
>> >>
>> >> > Does anyone have a better idea how to go about it?  I cant see how
>> >> > PostGIS maintains topology, but it obviously does somehow.
>> >> >
>> >>
>> >> It is fairly ridiculous but works. If you can get the data into an OSM
>> >> style XML file then the script in utils/simplify/simplify.pl will do
>> >> this for you. Specify a fairly small minimum feature size e.g.
>> >> --simplify=0.00001 which should get rid of any nodes within about 1m
>of
>> >> each other.
>> >>
>> >> The script is quite memory hungry on larger data sets. If this is an
>> >> issue then I may be able to provide a C implementation at some time in
>> >> the future.
>> >>
>> >>         Jon
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >
>> >
>> >--
>> >Nick Black
>> >--------------------------------
>> >http://www.blacksworld.net
>> >
>> >_______________________________________________
>> >dev mailing list
>> >dev at openstreetmap.org
>> >http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
>>
>>
>>
>
>
>--
>Nick Black
>--------------------------------
>http://www.blacksworld.net






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