[OSM-dev] Creating 3-d connected network from ways + layer tag

[Ben Supnik]

Hi Y'all,

First: this discussion is a liiittle bit different from my original 
intention (not that that's a bad thing).

I am trying to use the existing data and come up with a "best 
interpretation".  Since I will use the entire planet file, manual 
correction of persistent problems is not a short-term viable option. :-(

In particular, I expect both under-noding and over-noding.

Over-noding: a node connects two ways that cross at different altitudes 
(as hinted by layer or bridge tags)...this happens in the TIGER imports 
(since TIGER is topologically integrated before export) so unless users 
have specifically fixed this, it'll be there...for every single overpass 
and bridge in the United states. :-)

(Since Tiger doesn't include layer information I don't see how anyone 
could have automatically fixed this...without layers you can't know 
which nodes are "false".)

Under-noding: I don't know how much existing software will fail to 
intersect two nodes...an artifact of my import is "fixing" all this 
(which gives me the over-noded case, although I could easily detect this 
by flagging nodes added by me at intersections).

Second: double-decker bridges I think open a bucket of worms:

- Do the two layers share the colocated nodes?  Is this even legal?
- How well do the editing programs let you manage such a beast?
- How well do the maps render it?

In Boston I see that the double-decker part of I-93 does not overlap 
itself...in practice such a map would be pretty unreadable so it doesn't 
surprise me that the data is how it is.

So far I think any candidate heuristic I have looked at for building a 
3-d network from the data would manage a double-decker road in a 
reasonably sane way.

cheers
Ben


Apollinaris Schoell wrote:
> On Jul 30, 2009, at 8:46 AM, Igor Brejc wrote:
> 
>> Apollinaris Schoell wrote:
>>> On 29 Jul 2009, at 22:05 , Igor Brejc wrote:
>>>
>>>> Karl Newman wrote:
>>>>> The topology rules are simple--if the ways share a node, then  
>>>>> they are
>>>>> connected and it is possible to navigate from any of the connected
>>>>> ways to another (subject to turn restrictions, etc.) The layer  
>>>>> tag is
>>>>> primarily a hint for renderers for proper display of vertically
>>>>> separated features. If the data is otherwise, then it is an error  
>>>>> and
>>>>> should be corrected.
>>>>>
>>>> Then how do you handle double-decker bridges?
>>>> (http://en.wikipedia.org/wiki/Bridge#Double-decker_bridge)
>>>>
>>> 2 ways with different layer number
>>>
>> I was asking more about the "sharing/not sharing nodes" stuff  
>> between those two ways
>>
> 
> can't think of a case where they could share a node. only if we start  
> to map an elevator between the 2 ways. but then osm needs to extend to  
> a 3d model. mapping 3d with elevation tag might be to simplistic....
> 
> at the end of the bridge when the 2 ways can merge into one again then  
> topology rule applies as outlined by Karl
> 
> 
>> Igor
>>
>>
>> -- 
>> http://igorbrejc.net
>>
> 
> 
> _______________________________________________
> dev mailing list
> dev at openstreetmap.org
> http://lists.openstreetmap.org/listinfo/dev
> 

-- 
Scenery Home Page: http://scenery.x-plane.com/
Scenery blog: http://xplanescenery.blogspot.com/
Plugin SDK: http://www.xsquawkbox.net/xpsdk/
X-Plane Wiki: http://wiki.x-plane.com/
Scenery mailing list: x-plane-scenery at yahoogroups.com
Developer mailing list: x-plane-dev at yahoogroups.com