[talk-au] Mini Roundabouts.

David Murn davey at incanberra.com.au
Fri Apr 30 05:46:56 BST 2010


On Fri, 2010-04-30 at 10:47 +1000, Ross Scanlon wrote:
> > 1) They're clearly mini roundabouts. I go straight over them on my bike.
> 
> They are concrete circles from Nearmap as far as I can tell.
> 
> > 3) Why an octagon shape? Ugh. At least use the "tidy" function in JOSM
> > or Potlatch to make them circles.
> 
> An octagon is the smallest number of nodes to accurately describe a circle.  And they have been tidied using JOSM's circle function.

I just had a quick look and noticed that too.  In the small area linked,
I counted 9 roundabouts.  Turning them into a circle, has given them 18
nodes each.  Given that each round-about has 4 entry/exit points, this
means for a diamond shape, youre using no extra nodes, for an octagon
youre using 36 extra nodes and the current method (18 nodes) has created
126 extra nodes in this area.

While I agree that its useful to represent curves and bends properly in
the traffic flow, this seems a bit excessive.  Youre going from having 9
roundabouts with 36 nodes, to having 9 roundabouts using 162 nodes, for
no reason other than so it renders a little bit nicer?

One question I do have though, is why put the roundabouts in, and not
split up the entry/exit ways?  From looking at the nearmap imagery, the
entry/exit lanes are divided at each round-about.  There also appears to
be a lot of footpaths in the area if youve got plenty of time to kill :)

David





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