The key:turn <http://wiki.openstreetmap.org/wiki/Key:turn> has values for slight_left/right and sharp left/right. There are no signs associated to these four values. I also couldn't find any corresponding signs on this page: http://en.wikipedia.org/wiki/Comparison_of_European_road_signs. The rationale of these values is missing on the key:turn page. What is the rationale?
One rationale could be to help the router in the following instructions: turn sharp right, turn right, bear right, take the exit right However, these values should then have to be applied on every turn. And routers do have a calculation for these: turn sharp right = turn angle < 90 degrees, turn right = about 90 degrees, bear right = > 90 degrees, take the exit = the _link on motorway/trunk exits. I suppose routers also use streetnames, to determine automatically if there's a turn onto a different street since nobody likes to hear 'straight on' too often when there's a slight angle in the road ahead. Since the routers can calculate these instructions based on a turning angle, it's somewhat strange to use values for it. A second rationale could be to help the router in displaying a lane assist. But, lane assist is correlated with traffic signs. So through, right and left are perfect values for a lane assistant. But slight_left/right and sharp left/right? So, I can't figure out a proper rationale for these four values. Is there a rationale for these four values?
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