[mkgmap-dev] Ranking of relations

Fri Jan 26 10:50:15 GMT 2024

Dear all,
I want to generate an overlay map to be used as additional layer on a
Garmin watch. This layer can be turned on/off on the watch and should
show only bicycle routes (route=bicycle and route=mtb).
As most routes in openstreetmap are defined as relations I am using the
following rules in my bike-routes style:

*relations (file)*
# Route relations as additional transparent layer for:
#   bicycle
#   mtb

# bicycle routes
type=route & route=bicycle
     {
         apply
             {set route='${route}';set
route_name='$(route_name),${name}'|'${name}';set
route_ref='$(route_ref),${ref}'|'${ref}';}
     }
type=route & route=bicycle & network=icn            {apply {set
route_icn=yes;}}
type=route & route=bicycle & network=ncn            {apply {set
route_ncn=yes;}}
type=route & route=bicycle & network=rcn            {apply {set
route_rcn=yes;}}
type=route & route=bicycle & network=lcn            {apply {set
route_lcn=yes;}}

# mountainbike routes
type=route & route=mtb
     {
         apply
             {set route='${route}'; set
route_mtb_name='$(route_mtb_name),${name}'|'${name}'; set
route_mtb_ref='$(route_mtb_ref),${ref}'|'${ref}';}
     }

*lines (file)*
# bicycle routes
route=bicycle & route_icn=yes    {name '${route_ref}'}                
                             [0x10f01 resolution 18-22 continue]
route=bicycle & route_icn=yes    {name '${route_name}
(${route_ref})'|'${route_name}'|'${route_ref}'}    [0x10f02 resolution
23-24]

route=bicycle & route_ncn=yes                                        
[0x10f01 resolution 20-22 continue]
route=bicycle & route_ncn=yes    {name '${route_ref}'}                
                             [0x10f02 resolution 23 continue]
route=bicycle & route_ncn=yes    {name '${route_name}
(${route_ref})'|'${route_name}'|'${route_ref}'}    [0x10f02 resolution 24]

route=bicycle & route_rcn=yes                                        
[0x10f03 resolution 20-22 continue]
route=bicycle & route_rcn=yes    {name '${route_ref}'}                
                             [0x10f04 resolution 23 continue]
route=bicycle & route_rcn=yes    {name '${route_name}
(${route_ref})'|'${route_name}'|'${route_ref}'}    [0x10f04 resolution 24]

route=bicycle & route_lcn=yes    {name '${route_name}
(${route_ref})'|'${route_name}'|'${route_ref}'}    [0x10f05 resolution 24]

# mtb routes
route=mtb     {name '${route_mtb_ref}'}                                
         [0x10f06 resolution 23 continue]
route=mtb     {name '${route_mtb_name}
(${route_mtb_ref})'|'${route_mtb_name}'|'${route_mtb_ref}'} [0x10f06
resolution 24]

In general, these routes are drawn by mkgmap and I am able to generate
an overlay map, but sometimes a route with "lower" priority (i. e. a
route=mtb) hides a route with "higher" priority. In other words, I would
like to show the routes in a ranking: The routes tagged with network=icn
should be on top, followed by network=ncn and so on. The route=mtb
should be only shown, if no other bicycle route is on the same way.
Is this possible to achieve with mkgmap alone? Or do I need some sort of
additional script to rank the relations before rendering them with mkgmap?
I have read something, that the draw order depends on the ID of the
relation and mkgmap renders the lower IDs first. But what about the
higher relation IDs? It looks like ways tagged from the relation only
get the tags from the relation with the lowest ID. Is this correct?
Does anybody have an idea, how this could be overcome?

Example:
Way ID has 3 bicycle relevant relations: relation IDs 2119154,
9623717,2956920. With the style from above only the last one (relation
ID 2956920, route=mtb) is shown although the second one (relation ID
9623717, network=icn) would be desired as it is an international bicycle
route.

Regards,
Bernard
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