On 18/11/2012 21:59, Philip Barnes wrote:
On Sun, 2012-11-18 at 21:26 +0100, Colin Smale wrote:
Phil, there's a difference between routing calculation (which neither
knows nor cares about road names, numbers, signposts etc) and how the
result of the calculation is presented to the user. Then you need to
relate the nodes/edges in the routing graph back to the real world. The
value in this tag (as well as name, destination etc) is that the
navigation software can give instructions based on recognisable
landmarks instead of referring to way IDs. This distinguishes between
pure "routing" and "useful navigation".
Thats the point I am making, the most useful instruction a satnav can
give is "leave the motorway a junction 4", or words to that effect.
There is nothing more recognisable than the junction number.
Well, for a start junctions are only numbered on motorways and some
trunk roads. I think most people would consider "keep left on the A1001
towards Anytown" clear enough (assuming that's what's on the sign), with
or without a junction number. There has also been a discussion going on
(admittedly outside of the UK) about the use of destination:ref to store
the ref of the destination, so in this case we would have
destination=Anytown and destination:ref=A1001, plus junction:ref=5 or
whatever. By structuring the information in this way we give navigation
software the choice of how to present the data.
Colin
Phil
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