Artur, The meaning is the same in both versions, "gps_precision" and "radiuses" are "the size of 1 standard deviation of accuracy".
However, between 4.x and 5.x, the range that we check is a lot narrower. It turns out that in 4.x, the default was about 10x too large, which makes map-matching very slow because of the increased number of candidates that it needed to check. The smaller the radius you can use, the faster map-matching will be. There's no way to change the setting globally on the URL. You can change the code and re-compile OSRM if you want to modify the default. Not the best way to do it, but all we've got at the moment. daniel > On Jun 20, 2016, at 11:24 AM, Artur Bialecki <[email protected]> wrote: > > Hello, > > Thank you for the answer. > > Did the match algorithm change between V4.8.1 and V5.2.2? Given the default > settings for GPS accuracy (5), V4 seems to match roads in larger radius then > version V5. > > Also, is there a way to globally change the default GPS accuracy instead of > having to specify it for every point? > > Thanks you, > > Artur… > > > From: Daniel Patterson [mailto:[email protected]] > Sent: Friday, June 17, 2016 12:13 PM > To: Mailing list to discuss Project OSRM <[email protected]> > Subject: Re: [OSRM-talk] GPS Accuracy for match service > > Hi Artur, > > TL;DR - there's no direct conversion from HDOP to radius, that's not what > HDOP is. > > Just knowing HDOP isn't enough. HDOP is based on satellite position and > basically tells you "if you had perfect reception right now, the best > accuracy you could achieve would be X". Less-than-perfect reception will > also affect accuracy, and isn't part of the HDOP calculation. Number of > satellites in view, multi-path-error, etc, all contribute to inaccuracy and > aren't part of HDOP. > > Things like iPhones can give a reasonable estimate because they have a > known GPS device with known characteristics, and they're possibly monitoring > satellite count, signal-to-noise ratio, etc and doing a fancier calculation > than you get from simple NMEA sentences. > > Cheap GPS devices sometimes do something naive like 3-5m * HDOP ~= 95% > radius (2 standard deviations). It's not really correct, but if that's all > you've got, run with it. > > daniel > > On Jun 17, 2016, at 8:36 AM, Artur Bialecki <[email protected] > <mailto:[email protected]>> wrote: > > > Hello, > > In the documentation of the V5 match service it states that radiuses are > “Standard deviation of GPS precision used for map matching. If applicable use > GPS accuracy”. If I have HDOP, how would I convert it to the radius value. > > Thank you. > > Artur… > This e-mail message is confidential, may be privileged and is intended for > the exclusive use of the addressee. Any other person is strictly prohibited > from disclosing, distributing or reproducing it. If the addressee cannot be > reached or is unknown to you, please inform us immediately and delete this > e-mail message and destroy all copies. Thank you. > _______________________________________________ > OSRM-talk mailing list > [email protected] <mailto:[email protected]> > https://lists.openstreetmap.org/listinfo/osrm-talk > <https://lists.openstreetmap.org/listinfo/osrm-talk> > > This e-mail message is confidential, may be privileged and is intended for > the exclusive use of the addressee. Any other person is strictly prohibited > from disclosing, distributing or reproducing it. If the addressee cannot be > reached or is unknown to you, please inform us immediately and delete this > e-mail message and destroy all copies. Thank you. > _______________________________________________ > OSRM-talk mailing list > [email protected] <mailto:[email protected]> > https://lists.openstreetmap.org/listinfo/osrm-talk > <https://lists.openstreetmap.org/listinfo/osrm-talk>
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