[OSM-talk] non-linear ways

Andy Robinson Andy_J_Robinson at blueyonder.co.uk
Tue May 16 11:24:56 BST 2006


Just to add another complexity on this issue, for map rendering purposes I
will look to align the way or segments so that text placement via SVG
creation looks right. That will on many occasions conflict with what is
right for navigational use. Perhaps to be certain, we should generate the
navigational requirements on a separate set of keys. I.e. parse through the
data and add the direction to a new key and then edit those keys to be
correct for navigation.

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 Andrew Findlay
>Sent: 16 May 2006 10:22
>To: Simon Hewison
>Cc: talk at openstreetmap.org
>Subject: Re: [OSM-talk] non-linear ways
>
>On Mon, May 15, 2006 at 06:30:58PM +0100, Simon Hewison wrote:
>
>> It's non-linear because if you follow the direction of the segments as
>> they are laid down, some of them are facing 'backwards'.
>
>There are bound to be many places where this is unavoidable. As segments
>are allowed to be members of multiple ways, consider the case of a
>bridge that is shared by two footpaths which happen to be drawn in
>opposite directions:
>
>
>            Y
>            ^
>            |
>            |
>            |
>A---------->P=========>Q---------->B
>                       ^
>                       |
>                       |
>                       |
>                       X
>
>The way from A to B uses the P-Q segment 'correctly' but the X-Y way
>uses it 'backwards'. Creating two segments between P and Q seems
>silly when we are talking about a footpath bridge which may not be
>wide enough for two people to pass in the middle, so we are stuck
>with the 'backwards' segment.
>
>In some cases it may be possible to turn round all the segments on
>one way so that both use the shared segment in the same direction,
>but this will not always be possible.
>
>I think your algorithm will have to be more tolerant at nodes with
>more than two segments.
>
>Andrew
>--
>-----------------------------------------------------------------------
>|                 From Andrew Findlay, Skills 1st Ltd                 |
>| Consultant in large-scale systems, networks, and directory services |
>|     http://www.skills-1st.co.uk/                +44 1628 782565     |
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