[OSM-talk] Topology

Andy Robinson Andy_J_Robinson at blueyonder.co.uk
Thu Apr 26 19:32:43 BST 2007


Frederik Ramm [mailto:frederik at remote.org] wrote:
>Sent: 26 April 2007 6:40 PM
>To: Andy Robinson
>Cc: 'OSM'
>Subject: Re: [OSM-talk] Topology
>
>Hi,
>
>> Well, some nodes which might appear to be uninteresting (ie they simply
>> define the geometry of the way) actually carry interesting tags. However,
>> I've no idea whether the tag data on an object affects this discussion or
>> not :-)
>
>This is a problem we touched on in the paper as well.
>
>I agree with Artem that it would be desirable to make a distinction
>between points that are really needed "as objects" - because they denote
>an intersection, the beginning of a speed limit, or a phone booth - and
>points that are just there to define a shape.
>
>Points "as objects" can enter into relationships with other objects;
>"shape points" cannot.
>
>Since there is no distinction between the two at the moment (i.e. what
>you say, uninteresting-appearing points suddenly have meaning), it is
>easy to break things (e.g. I want to change the shape of a stretch of
>railway and accidentally move or delete a railway station). This could
>of course be fixed at editor level (simply give a different colour to
>nodes that have tags, assuming that having tags is what makes them
>"interesting").
>
>So, one could say that making the distinction in the database or data
>model is just a case of premature optimisation. I'm not sure, maybe it
>is, but currently I like the idea of explicitly defining: This is a
>point with a meaning (even if I don't give it meaning right now), and
>this is "just a point".
>

I can see your point, which raises two questions for me. 
Firstly, what benefit do we gain from the distinction between the two types
of point, especially if we can at a simple level warn editors that moving
nodes may impact the locative relevance of the information it holds (of
course there is always the option to store the original placement lat/lon as
tag values for the node as well, whether by history or physically).
Secondly, if I want to convert a point with no tags to one that has them can
the type jump ship to the other db form easy enough?

Cheers

Andy

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk

>Bye
>Frederik
>
>--
>Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'






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