[Talk-ca] Editing intersections on dual carriage-ways

Marc Provencher marc at marcprovencher.com
Wed Apr 7 18:07:04 BST 2010


I searched, but could find no tutorial on an agreed way of properly mapping
an intersection of two dual-carriage ways, ie an intersection of two
residential roads where the ways are divided by a center boulevard, along
with mini right turn ramps on all four corners (see picture link below).

http://provencher.smugmug.com/Other/Misc/Intersection/830343527_po6Yx-X3.jpg

In this picture, I think junction nodes B and G are not needed. Technically,
if your vehicle is at B, you are not even legally allowed to turn right
anyways. Same for G.

Another question that arises, and for which I haven't seen a definite
answer, is what to do about the "middle" segments in the intersection. In
the picture above, if Road1 and Road2 have the same name, then they could be
drawn as a contiguous road segment, going through A-B-C-D.

But what if Road1 ends at this intersection, and Road2 begins there as
well?  Do you draw Road1 all the way thru junctions A-B-C, and then draw
Road2 thru junctions B-C-D? After all, if I'm heading southbound and want to
turn left onto Road2, I would want my routing directions to say "turn left
on Road2", not "turn left on Road1", which it might say if the segment
between B and C only belongs to Road1.

I have seem much more complex intersections as well, with separate left turn
lanes. I somewhat fail to see the point in modeling the intersections so
accurately, if it doesn't really add anything to a routing GPS?

Thanks for sharing your thoughts and guidance on this.

-- 
Marc Provencher
marc at marcprovencher.com
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