[OSM-dev] OGC standards / Sql Server 2008 / OSM... help?

brendan barrett shogunz0r at gmail.com
Wed Feb 18 22:08:46 GMT 2009


Thanks Dermot

Is correcting it inside OSM the only way to deal with this kind of
data? If so, i'm thinking of compiling a list of all the ways that do
not comply, and then posting them somewhere so that we can all pick
them off one by one. There are a lot in Australia alone (using the
aussie export to get my testing done). I have a feeling that anyone
using Sql Server Spatial will have these issues.

Regards,
Brendan

On Thu, Feb 19, 2009 at 12:01 AM, Dermot McNally <dermotm at gmail.com> wrote:
> Hi Brendan,
>
> I've just looked at the piece of coastline in question and found two
> errors in it (both now fixed):
>
> * There was a duplicate node
>
> * At a different place, the coastline overlapped itself.
>
> I can see how these (particularly the overlap) could be confusing to
> the DB. It may be worth trying it again with the new data.
>
> Dermot
>
> 2009/2/18 brendan barrett <shogunz0r at gmail.com>:
>> Hi
>>
>> I've just signed up to the dev mailing list, and hopefully i'll catch
>> up by reading the archives. For now though I have a question and
>> please don't follow up with insults if you see the names Microsoft or
>> SQL Server :P
>>
>> I'm trying to render coastlines in an application that I am building.
>> The concept is simple: find the lines, and join them end on end until
>> you get an area. Now my problem is with OGC standards. I'm using Sql
>> Server 2008 *ducks for cover* and more specifically the new Sql Server
>> Spatial types (Geography and Geometry). Sql Server 2008 seems to be
>> pretty strict with OGC standards, and I am but a beginner when it
>> comes to OGC standards.
>>
>> The problem i'm having is with some coastlines in OSM that double back
>> on themselves. Like this one:
>>
>> This way http://www.openstreetmap.org/browse/way/13858554 doubles back
>> on itself with this node
>> http://www.openstreetmap.org/browse/node/130020792 having the same
>> latitude as this consecutive node
>> http://www.openstreetmap.org/browse/node/130020793.
>>
>> I think this is the reason for the way being invalid in Sql Server's
>> eyes. The MS folks have included the MakeValid() function which
>> "corrects" the way to comply with OGC standards, but this changes the
>> latitude and longitude of every point in the line ever so slightly,
>> and that's not desirable if you are matching ways end on end. I can
>> use the Node Ids to match them, but the bigger issue is that my data
>> is "invalid" and I can't use other spatial methods on it.
>>
>> I have 4 questions:
>> 1. Is this doubling back really an OGC restriction? It makes sense
>> that these ways don't double back because it doesn't serve any purpose
>> for a coastline (or for any line, you would expect even a path that
>> doubles back to be at least some distance apart, or simply labeled two
>> way).
>> 2. If this is a problem, is it something that will be fixed in the
>> editors / the API?
>> 3. Is there anyone else here with experience with SQL Server 2008
>> Spatial and OSM that might have some tips on dealing with all these
>> ways?
>> 4. Does PostGIS have these types of issues?
>>
>> I'm thinking that the only way for me to deal with this is to correct
>> the data in OSM (if it's clearly incorrect) or in my database once
>> imported (if there's no other solution).
>>
>> Thoughts?
>>
>> _______________________________________________
>> dev mailing list
>> dev at openstreetmap.org
>> http://lists.openstreetmap.org/listinfo/dev
>>
>
>
>
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