[OSM-dev] shp2osm.pl

Ian Dees ian.dees at gmail.com
Wed Sep 30 01:34:33 BST 2009


On Tue, Sep 29, 2009 at 6:58 PM, Anthony <osm at inbox.org> wrote:

> On Tue, Sep 29, 2009 at 7:35 PM, Ian Dees <ian.dees at gmail.com> wrote:
>
>> On Tue, Sep 29, 2009 at 6:09 PM, Peter Körner <osm-lists at mazdermind.de>wrote:
>>
>>>  > And I believe it has
>>> > been suggested to use boundary relations rather than polygons in cases
>>> > where there are a lot of overlapping boundaries.
>>>
>>> Yes, I'ts not good to have overlapping ways - they are a mess to edit
>>> and they can be constructed by relations, as well.
>>>
>>
>> I've been hoping someone would strike up a conversation with me on a good
>> algorithm to find and relation-ize overlapping boundary ways. I would love
>> to implement this...
>>
>
> Can we assume the shared ways use shared nodes?  I was planning on making
> that assumption, because I believe it's true for the particular data I'm
> trying to import.  Without that assumption, it's probably too much work for
> the time I have.
>

No. In most cases the ways do not share nodes. Almost all of the time, the
overlapping ways share node locations.

e.g.: Two neighboring square country borders: one with nodes a,b,c,d and one
with nodes w,x,y,z:

a--bw--x
|  |   |
c--dy--z

Nodes b and w are exactly overlapping, but are part of two different ways.


> In any case, I have to worry about converting the multipolygons from the
> shapefile I have first.  I'm pretty sure there are some, in the standard
> "holes go clockwise" format, and shp2osm doesn't handle that as far as I can
> tell.
>

My Java version of shp-to-osm handled this automatically. It appears to me
that the shapefile format follows the same model we do: clockwise for outer
rings and anti-clockwise for inner rings (e.g. "holes").
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