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<p>On 2020-05-25 00:16, Florian Lohoff wrote:</p>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">On Sun, May 24, 2020 at 11:54:02PM +0200, Colin Smale wrote:
<blockquote type="cite" style="padding: 0 0.4em; border-left: #1010ff 2px solid; margin: 0">On 2020-05-24 23:16, Mateusz Konieczny via talk wrote:<br /><br />
<blockquote type="cite" style="padding: 0 0.4em; border-left: #1010ff 2px solid; margin: 0">Can you give an example of such untaggable restriction?</blockquote>
<br /> In the UK there are many small roads signed as "Unsuitable for HGVs."<br /> Legally you are allowed to drive your 44T truck down there, but you will<br /> almost certainly get stuck. How do we tell the router?</blockquote>
<br /> width? maxwidth?</div>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">It needs to be a physical attribute, not a purely legal one. It could be a combination of road width and bends, or undulations giving a risk of grounding. For the former, the router would need accurate geometry info (centre line and width) which is often not present or not reliable in OSM. For the latter, do we have anything for "risk of grounding due to dips and humps"?</div>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace"><br /> It a different attribute than legalese which makes it unsuitable - so<br /> tag it appropriate.<br /><br />There are also many roads signed as "No HGVs except for access." It is<br /> tempting to tag them as "hgv=destination" but that doesn't cover the<br /> case where you are allowed to follow that route for many miles and make<br /> several turnoffs IF you "need access". The current definition of<br /> "access=destination" doesn't allow routers to distinguish between truly<br /> "first/last segment only" and "its fine if you are going to/from this<br /> general area". <br /> Discussion here shows the <br /><a href="http://www.trucknetuk.com/phpBB/viewtopic.php?f=5&t=140446" target="_blank" rel="noopener noreferrer">http://www.trucknetuk.com/phpBB/viewtopic.php?f=5&t=140446</a><br /> Thats a technical difficulty in the OSM Data model which may fill pages.<br /><br /> At least in Germany a restriction sign is not a "linear restriction"<br /> e.g. is restricting the whole way. Instead you may not traverse the<br /> point of the sign. We are currently unable to put this into OSM.<br /><br /> A workaround is to put 2 short oneways on top of each other - one of<br /> them carrying the restriction - which is in itself a pretty ugly<br /> solution - and - this does not work for destination.<br /><br /> There are other problems. A destination technically is currently solved<br /> by increasing the "cost" in the routing graph. So for example for<br /> every meter on a destination road you may travel 20m on others. Which<br /> most of the time works pretty well in avoiding the destination roads.<br /> It has pretty bad side effects which causes the router to try to send<br /> you out of the destination area with the shortest way even producing<br /> very long diverts around.</div>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">You talk as if all routers are the same.... I accept that such heuristics are inevitable to choose between multiple possibilities, but proposing a route that would actually be considered illegal should not ever happen (subject to data currency considerations).</div>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">But still, access=destination does not permit the router to apply different penalties to the two cases I mentioned.</div>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">Legally this is broken. Legally you may not enter the zone when<br /> your destination is not within that zone and there nothing like a <br /> distance based penalty within that area.<br /><br /> So yes - there is a problem - But not within tagging. Its something<br /> routers need to solve.</div>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace">Routers cannot work alone, they have to work together with the tagging. It's not fair to claim it's all their problem. If the tagging does not represent the nuances required, the router should not be expected to just guess (at least where the difference is between legal and illegal).</div>
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