mapcss parent_tag(key_name) only selects value from 1 parent

[Polyglot]

On the wiki I find the following:

parent_tag(key_name)

get the value of the key key_name from the object's parent(s)

It suggests that more than 1 value can be shown. (The use case is a bus stop which is a member of several routes)

I think it's coded here:

​http://josm.openstreetmap.de/browser/josm/trunk/src/org/openstreetmap/josm/gui/mappaint/mapcss/Expression.java

182            public String parent_tag(String key) {
183	                if (env.parent == null) {
184	                    // we don't have a matched parent, so just search all referrers
185	                    for (OsmPrimitive parent : env.osm.getReferrers()) {
186	                        String value = parent.get(key);
187	                        if (value != null)
188	                            return value;
189	                    }
190	                    return null;
191	                }
192	                return env.parent.get(key);
193	            }

I'm not a java coder so I don't dare to touch it myself, but couldn't it work with a loop and return a list of values in a string separated by ";"? What is a matched parent? One defined by the selector expression?

[Polyglot]

What do you think about this? It's untested and probably contains syntax errors, but it should be 'almost there'.

            public String parent_tag(String key) {
	                if (env.parent == null) {
	                    // we don't have a matched parent, so just search all referrers
	                    String value = "";
	                    for (OsmPrimitive parent : env.osm.getReferrers()) {
	                        value += parent.get(key) + ";";
	                    }
                            if (value != null)
	                        return left(value,len(value)-1); # remove trailing ';'
                            else
	                        return null;
	                }
	                return env.parent.get(key);
	            }

[bastiK]

Semicolon as separator is a little arbitrary, other user probably want space or space,dash,space.

Maybe a second function "parent_tags(String key, String sep)"?

[Polyglot]

I proposed semicolon because that's what I put in route_ref of our bus stops.

I was also thinking that a separate function would be even better. Extra brownie points for a user defined separator.

I didn't propose to have a separate function, as I don't know how that would fit in the general mapcss standard.

Jo

[Polyglot]

I've been reading up a bit on how mapcss is being implemented in other products. Am I correct if I deduce JOSM has more eval expressions than the other implementations at the moment i.e. parent_tag isn't available (yet) in the other implementations? And thus it wouldn't be a problem to create a separate parent_tags function?

If parent_count() is ever implemented, it probably needs a selector as well. I would only be interested in other PT relations when working with a style sheet dedicated to PT. Will it ever be possible to 'loop' over them? That would be terrific for creating 'spider' diagrams of PT maps. 1 route relation in its assigned color on the road, itself. Another next/above it and another beneath it.

For the time being I would already be happy with a list of colors that can be used to 'hash' the line. If 4 relations pass over a road, I'd like to be able to colour it in small 'segments' of each of the assigned colours. Of course, this doesn't make sense any more when there are more than say 5 or 6 relevant routes passing there.

[Aun Johnsen <lists@…>]

parent_tags() should probably return a list, and than list functions can be used to alter the list in whatever way you like, i.e. join(parent_tags(ref), ";") would give a ; separated string of all refs, while maybe the same user would like to see join(parent_tags(name), " - "), having parent_tags() return a list gives you all the flexibility of list functions to work directly on it.

[simon04]

In 8775/josm:

fix #8170 - MapCSS: add functions parent_tags(key) and join_list(sep, list)

The method parent_tags(key) returns all parent's values for key as a list ordered by a natural ordering.
The method join_list(sep, list) joins the elements of list to one string separated by sep.

[Polyglot]

Hi Simon,

Thank you for implementing this. I see you have a test case for a node and tags from its parent ways. I'm trying to make it work for a node which is a child of a relation. Unfortunately I only get 1 result, instead of a longer list.

relation[route=bus] > node|z16-::parent_ref
 {text-color: pink;
  font-size: 19;
  text: join_list(";", parent_tags(ref));
  text-halo-radius: 2;
  text-offset-y: -40;
  z-index:5.0;}

I'm testing on this node: ​https://www.openstreetmap.org/node/2956645204

[simon04]

This relates to the general behavior that only one child/parent is matched by the child/parent selector. Then, env.parent != null and simply Collections.singletonList(env.parent.get(key)) is returned. I do not see a simple solution for that at the moment …

[Klumbumbus]

It is not the same what you would like to achieve, but this maybe helps you:

relation[route=bus] > node::parent_ref {
  set busroutenode;
}

node|z16-.busroutenode::parent_ref {
  text-color: pink;
  font-size: 19;
  text: join_list(";", parent_tags(ref));
  text-halo-radius: 2;
  text-offset-y: -40;
  z-index:5.0;
}

[Polyglot]

Wouldn't it be possible to simply drop

if (env.parent == null) {

as a condition? The whole point of trying to fetch a tag of all the parents is that the matched parent is irrelevant.

I see another problem appearing. What if the same ref is present in several parents, like on this node:

​https://www.openstreetmap.org/node/80724709

It's an extreme example... A very busy bus stop.

Jo

[simon04]

The problem with env.parent == null is that the role selectors (relation >[role=...] node[public_transport]) don't have any effect. Neither solution is satisfying, before having #7151 resolved.