[Tagging] Draft Proposed Relationship Area Steps

Martin Koppenhoefer dieterdreist at gmail.com
Thu Mar 5 10:57:48 UTC 2015

2015-03-05 10:20 GMT+01:00 Tobias Knerr <osm at tobias-knerr.de>:

> My impression from previous discussions of the topic was that the steps'
> shape within the area is hard to define.

usually you will be able to connect the first (and further any n-) node of
the upper and lower ways and divide them by (step_count-1) (if given).
These are the intermediate projections of the risers (i.e. what you
typically draw as lines in a technical drawing). Now for the scales we use
in OSM typically, this would very likely result in too narrow line
distances for common zoomlevels, so you'd probably omit half or two-thirds
(or even more) of the lines for rendering. This all depends of course how
big the single steps are. For reference, typical steps are 27-30 cm large,
outside 30 is quite normal, because they tend to be around 15-16 cm high
(and this determines the ideal largeness).

> You propose the restriction
> that the upper and lower boundary need to have the same number of nodes.

I had proposed this because it would make rendering easiest. It is not
strictly necessary though, you could also compute more complicated
algorithms that use e.g. intermediate nodes in the ways according to the
distance to the starting node. It doesn't matter for straight steps, but
will matter for curved ones or ones that have angles. If the amount of
nodes is equal it will be most probably the best idea to use these existing
nodes for the interpolation of the steps.
My proposal (this one here is basically an excerpt) didn't require equal
node amounts, it just encouraged the users to do it like this.

Regarding the steepness of the steps and how to map them, I'd not only
suggest to use "incline" with a percentage (like it is currently done in
the area steps proposal) but also permit to enter the height and largeness
(sorry for my English, this is intended as the projected distance of two
consecutive risers) of a single step (projection of riser) because these
tend to be the same along the whole steps (otherwise people risk falling),
and they are easier to survey (no need to calculate).
For who reads German, here is an interesting article in wikipedia about
this aspect of steps: http://de.wikipedia.org/wiki/Treppensteigung

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