[mkgmap-dev] [PATCH] apply_once

Mon Jan 4 06:35:09 GMT 2010

On Sun, Jan 03, 2010 at 11:10:02PM +0200, Marko Mäkelä wrote:
> On Sun, Jan 03, 2010 at 11:33:36AM +0200, Marko Mäkelä wrote:
> > Steve, all,
> > 
> > Some relations legitimately contain elements in multiple roles.
> > An example is bus routes that partially coincide with oneway streets
> > or roundabouts.  These are best drawn as closed loops that do cover
> > the twoway streets twice (once in role=forward and once in role=backward).
> > 
> > The attached patch implements an apply_once keyword that will apply the
> > commands only once per matching relation member.  OK to commit?
> 
> If nobody complains, I will commit the apply_once tomorrow.

Actually, I think that we will need deep_apply and deep_apply_once as well.
These would recursively execute the set/add commands on member relations too.

This is necessitated by the fact that according to these wiki pages:
http://wiki.openstreetmap.org/wiki/Relation:route
http://wiki.openstreetmap.org/wiki/Buses

the role=stop members of a transit relation should be nodes on the ways
that constitute the route, not POIs defined for passenger waiting areas
(such as highway=bus_stop next to the way).

Because some applications are interested in the passenger waiting areas
and others are interested in the vehicle stop areas, a scheme has been
proposed where type=stop relations are defined for the stops, grouping
the vehicle stop node and the passenger wait area.

I implemented this for one ferry route so far:
http://www.openstreetmap.org/browse/relation/155054

Without deep_apply, I guess that the outcome would be nondeterministic.
Even if the style file defined separate commands for type=stop relations,
it would depend on the evaluation order whether the set/add commands
would be executed on the type=stop relations for a type=route relation
before the set/add of the type=stop relations would be executed on the
member nodes.

At http://wiki.openstreetmap.org/wiki/Relation:route I understood that
this could also be useful for route relations that consist of smaller
route relations.  The names of the super-relations could be added to
the members with a deep_apply_once statement.

If nobody complains, I will add apply_once, deep_apply and deep_apply_once
to the style language and add something like this to the default style:

relations:
+type=route
+& (route=bus|route=trolleybus|route=ferry|route=subway|route=train|route=tram)
+& (ref=* | name=*)
+{
+  add ref='${name}'; # if ref is missing, use name
+  apply_once { set route_ref='$(route_ref),${ref}' | '${ref}' }
+}

(the apply_once would be replaced with deep_apply_once)

Index: resources/styles/default/points
===================================================================

--- resources/styles/default/points	(revision 1457)
+++ resources/styles/default/points	(working copy)
@@ -97,6 +97,9 @@ amenity=townhall [0x3003 resolution 21]
 amenity=university [0x2c05 resolution 21]
 amenity=zoo [0x2c07 resolution 21]
 
+route_ref=* &
+(highway=bus_stop | railway=tram_stop | railway=halt | railway=station)
+{ set ref='${ref|def:}(${route_ref})' }
 (highway=bus_stop | railway=tram_stop | railway=halt | railway=station)
 & lit=yes & (shelter=yes | covered=yes)
 { name '${name|def:} ${ref|def:}*${operator|def:}'; }

Best regards,

	Marko

