Routing errors in London

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Re: Routing errors in London

Postby Twister-UK » Fri Jul 26, 2013 10:42 am

Twister_UK wrote:I left the script running this morning, so fingers crossed we should end up with a full 24-hour log of this route later tonight...


Sadly, script-o-matic Mk.1 was quickly hacked together in such a way that, if Livemap failed to return any routes, it'd require manual intervention to continue logging, and at just after 8am yesterday Livemap, not unexpectedly, failed to return any routes...

The all new and improved script-o-matic Mk.2 (cleans whiter than white, with 33% fewer calories, using the latest nanoparticle formulation) should now be able to resume logging automatically once valid routes are available again. It's been running on the same route since just before midnight yesterday, so at the very least I'll be able to compare the early morning results for two consecutive weekdays - be interesting to see if that 01:00-02:30 route shortening occurs again.
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Re: Routing errors in London

Postby seriousarsonist » Thu Jul 25, 2013 10:17 am

That's really very cool indeed!
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Re: Routing errors in London

Postby Twister-UK » Thu Jul 25, 2013 10:07 am

Bit of GIMPing (doesn't sound nearly as cool as Photoshopping...) gives us a mapped out view of all the endpoints for the above data

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The red dot shows the true endpoint (it appears I actually set it to a side road just off the B219, rather than the B219 itself...), and the blue dots show all of the incorrectly generated endpoints for the quickest routes within the yellow area of the earlier plot.
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Re: Routing errors in London

Postby dknight212 » Thu Jul 25, 2013 9:17 am

A-MAZ-ING
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Re: Routing errors in London

Postby Twister-UK » Thu Jul 25, 2013 9:09 am

Early results from the first bit of script-o-matic testing...

Routing from my old favourite, Games Lane in Cockfosters (51.65501626,-0.156668998) down to the B219 in Peckham Rye (51.45954977,-0.06766258), logging started at 23:00 yesterday, with the script requesting a recalculation of the route (approximately) every minute.

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This is a plot of the route distances (blue = quickest, red = shortest) against time. Where the plot background changes to yellow, this indicates results where the two routes differ in their endpoints. For each result, the shortest route always reached the requested endpoint, so differences in the endpoints are entirely due to the quickest route failing to reach that endpoint. Whilst checking the progress of the script this morning, I could see on the Livemap window that the quickest route was falling well short of the endpoint - there was clear space between the two endpoint marker flags. I could also see that, at one or more points along the route, Livemap was reporting heavy traffic, whereas when I kicked off the test last night the map was clear of traffic issues.

Interesting also to note that period between 01:00 and 02:30ish where the quickest route manages to shed around 10 miles yet still reach the destination correctly.

I left the script running this morning, so fingers crossed we should end up with a full 24-hour log of this route later tonight...
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Re: Routing errors in London

Postby dknight212 » Wed Jul 24, 2013 11:53 am

Twister_UK wrote:
Something else that crossed my mind regarding the interaction between the routing algorithm and the traffic data - since the traffic data changes quite frequently at certain times of the day, I wonder if the routing code takes a snapshot of the data before starting to generate each new route, or if it just assumes that the live data isn't going to change significantly during the calculation of the new route. If the latter, then there's always the chance that during the calculations the data has changed in such a way that the intended route breaks whatever internal thresholds/sanity checking are set for the routing code.

Given that it generally seems to be the quickest route option that starts to fall short of the intended destination before the routing code gives up completely, this would tie in with it being traffic data related - the shortest route would only be affected if the road closure data got updated during the routing calculation, whereas changes in traffic density shouldn't affect it at all (it doesn't care how long it takes to get from A to B...).


Good thinking, could test by rerunning the same route several times?
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Re: Routing errors in London

Postby Twister-UK » Wed Jul 24, 2013 11:51 am

dknight212 wrote:Chris - I think you have these tests scripted now, is that right? Is it very difficult to tabulate these results so Waze HQ have an easy reference for their checking? No worries if not.

Ideally something like: start lat/lon/street, finish lat/lon/street, time of day, success/fail, distance A, distance B


I haven't automated any of it yet, but it's something I was mulling over this morning...

Just shoot me if I'm asking too much!


Inbound, weapons hot :mrgreen:


Something else that crossed my mind regarding the interaction between the routing algorithm and the traffic data - since the traffic data changes quite frequently at certain times of the day, I wonder if the routing code takes a snapshot of the data before starting to generate each new route, or if it just assumes that the live data isn't going to change significantly during the calculation of the new route. If the latter, then there's always the chance that during the calculations the data has changed in such a way that the intended route breaks whatever internal thresholds/sanity checking are set for the routing code.

Given that it generally seems to be the quickest route option that starts to fall short of the intended destination before the routing code gives up completely, this would tie in with it being traffic data related - the shortest route would only be affected if the road closure data got updated during the routing calculation, whereas changes in traffic density shouldn't affect it at all (it doesn't care how long it takes to get from A to B...).
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Re: Routing errors in London

Postby dknight212 » Wed Jul 24, 2013 6:34 am

Chris - I think you have these tests scripted now, is that right? Is it very difficult to tabulate these results so Waze HQ have an easy reference for their checking? No worries if not.

Ideally something like: start lat/lon/street, finish lat/lon/street, time of day, success/fail, distance A, distance B

Just shoot me if I'm asking too much!
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Re: Routing errors in London

Postby faitaru » Wed Jul 24, 2013 4:30 am

I've always thought the errors occur when the recommended route is significantly longer than the crow flies (rather than an alternative route).

It's going to be related to the problems you get routing between peninsulars; for example Barrow to Morecambe, Shoebury to Whitstable, Ilfracombe to Swansea.

Only difference is the cross city London routes have a straight line alternative, but I'm sure the problems with the longer Circular routes is the same.
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Re: Routing errors in London

Postby Twister-UK » Tue Jul 23, 2013 10:18 pm

CTCNetwork wrote:Would this have anything to do with the time that the routing is done? Is it confined to a particular time/s of day?


Testing in the mornings (6-7am) and around lunchtime (12-2pm) is when I see routing errors occurring, whereas testing in the evening (9pm onwards) seems to be pretty solid.


I've been running another quick test, leaving the start and end points unchanged and just calling the navigate() function from the console. Although I haven't been getting any errors (as expected given the time of day), I have noticed the routes returned change slightly every now and again, and I'm guessing this is the routing engine adjusting to the live traffic conditions out there right now.

Presumably then, during those times of the day when traffic conditions are more changeable (i.e. the start of the morning rush hour and throughout the working day), the routing engine will have more live data to contend with whilst trying to calculate its routes, and so maybe this is where the problem lies?
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