Translating OSM 'osmc:symbol' into symbol geometry with QGIS

Question

OpenStreetMap uses specific tags to describe route symbols that are used as waymarker (https://wiki.openstreetmap.org/wiki/Key:osmc:symbol).

For example: "osmc:symbol"=>"red:white:red_dot"

I would like to translate that key syntax into a symbol geometry with QGIS similar to the OSM composer does (https://wiki.openstreetmap.org/wiki/OSM_Composer). But the only idea I get into my mind is:

1. build SVG-symbols for every possible combination (with Inkscape)
2. Name every symbol with the relating key (like 'red_white_red_dot.svg')
3. Use data defined override at an SVG marker line, where the SVG markers path is set up with the osmc:symbol field from the attribute table

That seems to be a not very elegant solution: Too static, too much work and too inflexible.

I'm looking for a better solution. Any ideas?

Answer 1

The logic in the tagging (osmc:symbol=waycolor:background[:foreground][[:foreground2]:text:textcolor]) can be translated into symbology using the rule-based styling.

Make a layered style and define a rule for every part of the osmc-tag using regex or QGIS-build-in string-expressions.

Or you can 'explode' the tag into different attributes, based on the delimitter ':' (by using eg. virtual fields). An example of splitting based on a ',': Splitting field with comma as separator into two fields in QGIS. Then you can assign a symbol based on the values you extracted.

--- EDIT ---

In QGIS 3 this is less complicated with the array-expressions that are provided since.

array_get(string_to_array('red:white:red_dot',':'),0) returns 'red' array_get(string_to_array('red:white:red_dot',':'),1) returns 'white' array_get(string_to_array('red:white:red_dot',':'),2) returns 'red_dot'

Use string_to_array() splitting on : to make an array ['red', 'white', 'red_dot']

Use array_get() combined with 0 to get te first part, 1 to get the second part, etc.