wendorff at uni-paderborn.de
Thu Aug 26 22:21:26 BST 2010
Thanks for your reply - I'll comment your (shortened) mail in between.
On 26.08.2010 22:47, David ``Smith'' wrote:
> On Thu, Aug 26, 2010 at 4:25 PM, Peter Wendorff
> <wendorff at uni-paderborn.de> wrote:
> Makes sense to me. You might consider one minor modification, though:
> maybe we could add a couple of disambiguation words to the name for
> sidewalks. For example, an east-west street called Drury Lane might
> have sidewalks called Drury Lane North Sidewalk and Drury Lane South
> Sidewalk. This disambiguates the sidewalks from the street and from
> each other.
Well... if a sidewalk has a dedicated name I would have mapped it as
separate way without tagging it as a sidewalk, as it's another way by name.
Adding "south" "north" etc. to sidewalks is not a good idea. If an
application needs this data, it has to get the geometric relation
between sidewalk and street to add north/south/west/east or - if
preferred left/right (depending on the walking direction).
> Some other points that may well have already crossed your mind:
> * If a street has its sidewalks mapped separately, the street itself
> should probably be tagged with foot=no.
That's possible and should be recommended, yes.
> * This provides an opportunity to characterize each sidewalk/street
> crossing (crosswalk). On the node where they intersect, tags could be
> used to indicate whether there is a dedicated crosswalk signal tied to
> the traffic signal, or if the traffic signal implicitly governs the
> crosswalk too, or if there is no such signal. There can be tagging
> for audible signals. Of course, if there simply is no crosswalk on
> that side of the intersection, then the sidewalk shouldn't be mapped
> between the two corners concerned. This information can be extremely
> useful to navigation for the blind.
;) I know.
I tag crossings as a line of 5(!) nodes - let's call them A,B,C,B,A.
C is the node shared between street and crossing footway. it's tagged as
crossing_ref=zebra|pelican... if one fits
if crossing=traffic_signals is applied, additional tags are:
The nodes B describe the border between sidewalk and street. Thus they
are tagged as
where * can be an arbitrary height in metric dimension. The numbering
scheme is proposed by the wheelchair-routing people, because wheelchair
users need to know the exact height of the curb to decide wether they
can drive up/down there. For blind people the reduced tagging scheme is
enough and that's easy for the mappers as it's possible to collect these
data without measuring (even from the bus).
primitive is applied where there is a tactile paving, but not made of
"THE" tactile paving stones. Often small cobblestones are used instead.
The A nodes are the connectors to the sidewalks on both sides of the
It's not correct to merge A and B node to one node, because that could
lead to a tactile paving not connected to the specific crossing.
I hope, I didn't forget parts of the crossing tagging I apply currently ;)
> * Instructions generated by a blind-navigation program, particularly
> when based on data with streets and sidewalks separated, should almost
> certainly include instructions like "Cross Drury Lane".
Yes, exactly - and therefore explicit tagged crossings are necessary.
Crossing a street is really dangerous in most cases for blind people.
Being able to get best crossing places at the street is the one and only
solution to get best possible security at that point.
If you want, look at the streets and crossings I mapped here. Most
footways should be tagged no (the sidewalk scheme is not applied yet,
sidewalks are unnamed there). Link:
Note: the footways often are not visible because they are hidden by the
streets. I tried to locate footways in a distance to the streets as they
are (street.width/2+sidewalk.width/2), but streets are rendered wider
than they are in most cases.
More information about the Tagging