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Hi Daniel,<br>
<br>
Your idea is pretty much what I used for my travel time map:
<a class="moz-txt-link-freetext" href="http://stvno.github.io/page/bartholomap/">http://stvno.github.io/page/bartholomap/</a> though N was easier to
determine: nearest non-stop airport, nearest one stop airport etc. <br>
For overland speed: I like the wiggle factor Bjorn was suggesting,
however it supposes we know the landuse, which as far as I know OSRM
doesn't take into account<br>
For N if we can have a default of 4 on separate roads that would
probably help a lot already without too high a cost. (separate roads
being at least one fork in the road away) Does that sound
reasonable?<br>
<br>
I guess the strategy to determine the N points could be made
configurable, different use cases require different strategies I'd
say.<br>
<br>
Steven<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 4/19/2016 4:44 PM, Daniel Patterson
wrote:<br>
</div>
<blockquote
cite="mid:CANvddSL8BeO-LHYnnoeWNYR7_27FNZfRQ6L6yn+fVhfzS7OULw@mail.gmail.com"
type="cite">
<div dir="ltr">Hi Steve,
<div><br>
</div>
<div> I was thinking about exactly this just the other day when
considering <a moz-do-not-send="true"
href="https://github.com/Project-OSRM/osrm-backend/issues/2277">https://github.com/Project-OSRM/osrm-backend/issues/2277</a></div>
<div><br>
</div>
<div> What I came up with was roughly:</div>
<div><br>
</div>
<div> Find N nearest neighbours, and calculate the walking
duration to each</div>
<div> Insert all neighbours into the search heap, and set the
initial cost to the walk duration</div>
<div> Route as normal, but include the walk duration in the
total time at the end</div>
<div><br>
</div>
<div> The question is, how big do we make N, and how do we
determine the overland speed? Overland speed I suppose could
be a profile parameter, and it feels like walking speed would
usually be the most appropriate thing. But I'm not sure how
many possible start points we should reasonably consider.
Everything within a radius? Closest N points?</div>
<div><br>
</div>
<div>daniel</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Apr 19, 2016 at 12:39 PM,
Steven M. Ottens <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:steven@minst.net"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:steven@minst.net">steven@minst.net</a></a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi all,<br>
<br>
I am working on a tool that will calculate the travel time
from villages to for instance the nearest hospital for rural
accessibility analysis. So far I have build a tool which
will calculate this for 215.000 villages in a few minutes,
thanks to the help of Daniel P. However I realized that not
all villages are on a road, actually quite a few are at
least an hour walk from the nearest drivable road see: <a
moz-do-not-send="true"
href="http://stvno.github.io/img/OSRM-snapping.png"
rel="noreferrer" target="_blank"><a class="moz-txt-link-freetext" href="http://stvno.github.io/img/OSRM-snapping.png">http://stvno.github.io/img/OSRM-snapping.png</a></a><br>
The villages are typically connected to the roads by
informal trails, which I do not have as a road network. So I
was wondering if it would be possible to add a basic penalty
to the distance of the point to the nearest road.<br>
I am aware that the nearest service will provide me with the
distance: <a moz-do-not-send="true"
href="https://github.com/Project-OSRM/osrm-backend/wiki/New-Server-api#service-nearest"
rel="noreferrer" target="_blank">https://github.com/Project-OSRM/osrm-backend/wiki/New-Server-api#service-nearest</a>
but before I am going to calculate the extra traveltime for
each village, I was wondering if it is possible to integrate
this with an osrm.table request. I am aware this opens quite
a can of worms: if there is a penalty to snapping, it might
be worth it to snap to a road which is further away, but in
the end quicker to get to the destination. But for the
moment I'm happy with just the added traveltime for nearest
road snapping.<br>
<br>
Any suggestions on how to handle this?<br>
<br>
Steven<br>
<br>
<br>
<br>
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</blockquote>
</div>
<br>
</div>
<br>
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