[Geowanking] Interpreting dual carriageways

[Michal Migurski]

Hm, I hadn't considered the buffer idea - that may work pretty well  
actually. The trick is to detect the presence of two ways to begin  
with - I can see if there are multiple OSM IDs present, but they may  
represent two ways placed end-to-end rather than side-by-side. I'll  
see what can be done with a buffer, on an intersection or maybe even a  
whole line segment.

-mike.

On May 17, 2009, at 11:51 PM, Guillaume Sueur wrote:

> Hi,
>
> If I understand your problem correctly, you want to get an ordered  
> list
> of single intersections along a street. IMO you should first get the
> list of all intersections, with their order, x,y, to_street and
> from_street items. Then, apply a filter which could work either way :
> 	- delete consecutive intersections involving the same streets
> 	- delete identical intersections within a buffer
> or maybe even both ways together.
>
> Hope that helps
>
> Regards,
>
> Guillaume
>
> Michal Migurski a écrit :
>> Hi,
>>
>> This is a geometry question.
>>
>> I'm working on a personal project using OpenStreetMap data that  
>> requires
>> a cross street index, that is, an ordered list of every intersection
>> along a street. I have it working fairly well, but I'm running into a
>> wall with dual carriageways. Here's an example from Oakland:
>>
>>    http://www.openstreetmap.org/?lat=37.80892&lon=-122.28339&zoom=17&layers=B000FTF
>>
>>
>> 14th Street crosses Adeline, Chestnut, Linden, Filbert, Myrtle, and
>> Market, but it does so twice and in two different directions. I've
>> gotten to a point where I'm able to extract a bundle of linestrings  
>> that
>> represent a length of road between two major intersections, e.g. 14  
>> St
>> between Myrtle and Market, but I'm having difficulty detecting and
>> correcting the potential presence of two overlapping carriageways.  
>> I'm
>> hoping to have something that can deal with regular single- 
>> carriageway
>> streets, this example of 14th St. in Oakland, places where a single
>> carriageway splits into two (e.g. to the west, where 14th crosses
>> Kirkham), and so on.
>>
>> I'm working in Python, with PostGIS and Shapely.
>>
>> I *think* what I'm aiming for is a near-parallel line detector, so  
>> I'm
>> experimenting with normalizing road orientation to zero and  
>> projecting
>> onto a straight line. It's getting squirrelly and I'm hoping  
>> someone can
>> help point to an existing approach to this problem.
>>
>> I'm open to the idea that there may be some manual intervention  
>> needed.
>>
>> -mike.
>>
>> ----------------------------------------------------------------
>> michal migurski- mike at stamen.com
>>                 415.558.1610
>>
>>
>>
>>
>> _______________________________________________
>> Geowanking mailing list
>> Geowanking at geowanking.org
>> http://geowanking.org/mailman/listinfo/geowanking_geowanking.org
>>
>>
>

----------------------------------------------------------------
michal migurski- mike at stamen.com
                  415.558.1610