[OSM-talk] Locks

[80n]

On 12/8/06, David Earl <david at frankieandshadow.com> wrote:
>
> I recently had occasion to add a couple of locks to the OSM.
>
> Currently the Map_features page says waterway=lock_gate is defined on
> nodes.
> That's fine for the creator (me), but it occurs to me that it will be hard
> to render when it comes to be done - assuming it would be represented as
> on
> a OS map for example...
>
> ----<-----<---
>
> - you'd have to determine which of the ways connected to the node are
> river
> or canal (very often footpaths go over lock gates, so there will be other
> things conected to the nodes; and what if there are more than two - if a
> weir section of the river goes off from that node too for example?)


A footpath shouldn't connect to the nodes that make up the canal.  That is,
unless, the footpath actually goes through the water ;)

If there is a branching channel then that could come from a very closely
adjacent node.

It should, imho, be a rendering error to try to draw a lock gate on a node
that has more than two segments connected to it.  There are other similar
cases, like gates, where the symbol should be marked by a node but drawn at
right angles to the path.

The direction the segments should determine the direction of flow of the
canal (as it does for rivers) and hence the direction in which to draw the
lock gates.



and then
> do something like compute the average angle between the two river/canal
> segements to decide at what angle to put the icon, and even then you don't
> know which is the higher side (which conventionally determines the
> direction
> of the symbol).
>
> Wouldn't it be better to define waterway=lock on a Way? Then rendering it
> becomes like a one way street - you just need to put the lock gate sybol
> at
> either end conventionally pointing in the directions of the end segments,
> the angle then depending on a segment, which is straightforward to
> compute.
> Usually this would be a single segment way of course (but in principle it
> could be more than one).
>
> David
>
>
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