[mkgmap-dev] Unusual Routing Behaviour in BaseCamp

Sat Nov 14 13:53:12 GMT 2020

Hi Ticker,

This is in the centre of Zambia so should not be affected by drive on right countries. Where Zambia borders drive on right countries such as Angola and DRC there are not likely to be any link roads particularly Angola as it is pretty remote and not many roads here anyway.

I understand the idea of a time penalty for a right turn across traffic, it is something that is always considered when driving in Lusaka normally as it is very congested, making a journey with all left turns will nearly always be quicker than one with a right turn across the traffic, the new flyover is part of a program to ease this. My interest was in the fact that bounds plus link tagging caused the problem,  bounds without link no problem, bounds plus any other tagging no problem. So the routing algo is obviously affected by the link even if it is following a direction away from the intended destination and then making a very tight right turn, tighter than 45 degrees that I am sure is illegal although not tagged with a no right tun in OSM. Following traffic regulations in Zambia is moot though and could endanger your life. I can live with the oddity.

In connection with the default style, for appearance sake it may be worth using a narrower type with service way roundabouts as the current style shows them in a size out of proportion to the connecting service ways. As space is not at a premium in Zambia many of the mall parkings have roundabouts within them  that are bigger than a mini roundabout, probably as big as a small roundabout in the UK.

Regards,
Dave

	  Original Message  	

From: rwb-mkgmap at jagit.co.uk
Sent: 14 November 2020 13:03
To: mkgmap-dev at lists.mkgmap.org.uk
Reply to: mkgmap-dev at lists.mkgmap.org.uk
Subject: Re: [mkgmap-dev] Unusual Routing Behaviour in BaseCamp

Hi Dave

There are a few things going on here that might have effects on the
routing behaviours you are seeing.

Driving side - as Gerd has elaborated. I have an example where the
Garmin routing algorithm will do 2 left turns, a u-turn and then a
right turn anyway across the traffic to avoid the correct, single,
right turn!

I notice that Zambia has adjacent countries with drive-on-right, so you
need to beware of tiles around the edge of your map where the automatic
choice could be wrong for Zambia.

The default style uses type 0x08 and 0x09 for link roads and these are
thought to have special properties regarding pop-up hints, but not
known to effect routing decisions.

Link roads have the same road_class as their non-link equivalents so
this shouldn't have drastic effect on routing, but they do have a lower
speed, which should have favored the direct turn even more (being
shorter as well).

Changing between primary and secondary might have a small effect on
which roads get their angle into/out-of the junction adjusted where
they are at a tight angle (<= 45 degrees) from another road and the
turn appear permissible for navigation - tight angles impose a routing
penalty.

Ticker

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