[OSM-talk] colour fills in osmarender

[Andy Robinson]

What all this points out is the difference between representing the physical
and modelling path patterns. At its heart, OSM is recording the physical
information. On top of this we layer additional data that provides
description and other information.

I would argue that the nodes and segments represent the physical, ideally we
would have curves as well but that is unlikely so we represent our physical
world in OSM using points and lines (or edges if you think GIS).

Probably 50% of the ways I have created in residential Sutton Coldfield have
been non-linear, in that they contain loops, multiple branches and the like.
This is because I define my way as one which represents the contiguous
physical street reference, normally its street name. If the named street
forks then so do my ways.

The result is, as Richard rightly pointed out, that what I have been mapping
for the physical world does not fit well with the algorithms required for
path modelling (ie navigation).

So, IMHO, OSM should record the physical and where this means that the
representation of the physical in OSM does not fit with the ideals of the
path models then something needs to be added to the nodes and segments that
permits the data to be used for path modelling. That could mean additional
ways used for this purpose or additional tagging to segments and nodes for
path analysis use.

Cheers,

Andy

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk 

>-----Original Message-----
>From: talk-bounces at openstreetmap.org [mailto:talk-
>bounces at openstreetmap.org] On Behalf Of Etienne
>Sent: 09 June 2006 11:46
>To: sxpert at esitcom.org; talk at openstreetmap.org
>Subject: Re: [OSM-talk] colour fills in osmarender
>
>On 6/9/06, Raphaël Jacquot <sxpert at esitcom.org> wrote:
>> Etienne wrote:
>>
>> > Are loops and branches in ways a good thing or a bad thing?   I can
>> > imagine that route planning applications might find them problematic,
>> >
>> > Etienne
>>
>> I believe we shouldn't have loops of any sort.
>> routing algorithms like to have straight simple topologies. loops add a
>> huge level of complexity that I don't think is necessary
>
>To do this, ways would need to be constrained so that segments can
>only be contiguous within a way
>(segment/@toNode=following-sibling::segment/@fromNode).  This would be
>a good thing IMHO.
>
>However, if you don't have ways with loops and branches then you don't
>really need segments at all.
>
>Some questions though:
>
>How would a roundabout be defined?  Is that a way or a point?
>
>Some roads, especially residential housing estates, can have roads
>that split and merge and branch, but only have one name.  How can that
>be achived economically?
>
>Etienne
>
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