[mkgmap-dev] Ferry line routing issue

Wed May 31 16:59:59 BST 2023

Hi.
I can experience the same type of issues (or at least very similar) on my 
GPSMAP 66st (handheld outdoor unit) when trying to take a ferry from the 
Scandinavian peninsula to Europe.
I have seen some of the jumps (straight lines occasionally).

Here is some theory on the issue.

Examples for such issues are Karlskrona (south of sweden) to Gdynia (north of 
Poland), or Stockholm to Helsinki. In those cases two the following can 
happen.

When calculating for time, the unit may consider to drive around instead of 
taking the ferry, the ferry entrance would just be a stop along the route but 
the device would not consider taking the ferry, because it is presumed slower 
than driving many 100 kilometers extra or it simply times out saying there is 
no route possible to calculate.

If i instead select calculating for shorter distance, the ferry is often 
considered and used by the route.

Anyhow, in the style file for lines, there are two entries for ferry lines:
route=ferry & (motorcar=no | motor_vehicle=no) [0x1b road_class=0 road_speed=0 
resolution 23]
route=ferry [0x1a road_class=3 road_speed=0 resolution 19]

If the ferry routes are expected to take cars the road_class will be 3 and and 
the road_speed 0, this road speed is so slow that the device will consider to 
use a faster way instead of taking the ferry.

So, what i do to make it a greater chance that a ferry will be used when 
routing for time, is that i have raised the road_speed to 1 for those two 
lines, since it would also help for passenger ferries. I was tempted to raise 
it to 2 but many ferries are too slow for road_speed 2.
This has somewhat improved routing scenarios in my case. It's not 100 % 
perfect but much better than before.

I cant say it is exactly the problem that you see, but some idea.

Regards
Karl

On onsdag 31 maj 2023 15:58:00 CEST Vukovics Mihály wrote:
> Hello Community,
> 
> I am struggling with an issue. I am generating Garmin map from OSM o5m
> sources(geofabrik) using the built-in style.
> Nor the BaseCamp or my Zümo 396LM is unable to calculate route via ferry
> lines. The behaviour is very strange, here is an example:
> 
> Route from Lille to Dover, all avoidances are disabled: unable to
> calculate route, just a straigth line between the citie.
> If I am forcing the route inside the service road area of Calais ferry
> terminal, the route is calculated correctly.
> Even funnier, that when I shape the route directly to the ferry line,
> Basecamp swims me on the ferry instead of routing through the port.
> 
> This behaviour is occuring with other ferry lines (for example Aberdeen
> - Lerwick).
> 
> I have checked on openstreetmap and the roads are connected and routable
> in the style file.
> 
> Here are the example screenshots about the issue.
> 
> https://picallow.com/mkgmap-ferry-routing/?usp_success=2&post_id=116783&form
> _id=27
> 
> Any ideas or fix?
> 
> Br,
> Mihaly
> 
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