tag:blogger.com,1999:blog-1564958057737541664.post758206629198961609..comments2024-02-14T17:11:22.168-08:00Comments on On Bicycles, and.... what else is there?: GPS accuracy comparison using Portola Valley Low-Key Hillclimb datadjconnelhttp://www.blogger.com/profile/01484858820878605035noreply@blogger.comBlogger15125tag:blogger.com,1999:blog-1564958057737541664.post-72679121380867698342014-11-15T21:45:31.826-08:002014-11-15T21:45:31.826-08:00GPS accuracy comparison using Portola Valley Low-K...GPS accuracy comparison using Portola Valley Low-Key Hillclimb data ... <a href="http://gpsforerunner.blogspot.de" rel="nofollow">gpsforerunner.blogspot.de</a><br />Wihelmhttps://www.blogger.com/profile/15515262368136130057noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-72533682432221466882014-01-02T16:21:31.965-08:002014-01-02T16:21:31.965-08:00That's a really good idea. Unfortunately I di...That's a really good idea. Unfortunately I didn't set the upload script to transfer altitude on this one. But I later fixed that. I have altitude in the Montara Mountain dataset. I'd need to collect the computer types for those, however.djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-34260109278927888462014-01-02T16:12:09.434-08:002014-01-02T16:12:09.434-08:00I realize this post is a couple months old, but it...I realize this post is a couple months old, but it would be really interesting to do a similar comparison with the altitude numbers.<br /><br />Diablo Scotthttps://www.blogger.com/profile/17186138821702336405noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-57493417764366193402013-12-04T20:07:15.110-08:002013-12-04T20:07:15.110-08:00Based on a Google map, I defined "lines"...Based on a Google map, I defined "lines" riders needed to cross to complete the course. These lines had a center point, and a right-hand-edge point, and a left hand edge the same distance but opposite direction from the center as the right. So I expected the rider trajectories to intersect these lines somewhere across the road. The lines were much wider than the road, however, to accomodate GPS error.<br /><br />So after determining the intercept of the rider trajectories with these "lines", I determined how far from the center the rider crossed each line. Of course the "perfect" answer isn't zero. But it is some small number of meters.<br /><br />So I calculated the root-mean-square such distance over the multiple checkpoint lines for each rider, then compared results based on the GPS unit the rider was using. The Edge 500's tended to be the largest crossing distances from the line-centers.<br /><br />If there's an error along the direction of travel, I wouldn't detect it: just lateral, perpendicular to the road direction, since my lines crossed the roads, versus running along them.<br />djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-58808412220622502622013-12-04T17:47:32.689-08:002013-12-04T17:47:32.689-08:00Dan this is great stuff. I wanted to ask for more ...Dan this is great stuff. I wanted to ask for more detail on how you computed the error in each person's GPS data. In your post you said, "I then compared these using the root-mean-square average of the distance from the center of the lines the riders triggered the lines (units: meters)." <br /><br />I've read this a few times and it's not clear to me what exactly you did. I'm also interested because I'm going to have my hands on both an Edge 500 and 510 next week and I wanted to quantitatively compare their GPS accuracy.jonahhttps://www.blogger.com/profile/06827304038127566936noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-89282153553134013832013-11-11T05:10:40.687-08:002013-11-11T05:10:40.687-08:00Great stuff, Michael!
I agree with everything.
W...Great stuff, Michael!<br /><br />I agree with everything.<br /><br />When I use my Android-based Droid Incredible to run Strava for nontrivial rides, I always run in Airplane mode, because of why you cite, and my battery is fatigued. I'm surprised how well it does.<br /><br />On the Edge 500: I agree. I like to believe it was my suggestion of "Last lap power" that was responsible for getting even that into the unit. You used to have to go through history, which was really terrible. As it is you can see only last lap power: no scrolling through laps. But it's still very useful: when doing an interval I want to see distance, time, power, lap-average power, and last lap power. For last-lap time or distance I need to wait. I do, however, like the form factor: it's light and small, unlike the clunkier Edge 510. So "black box" is close to true.<br /><br />On black boxes: I wish cars all had them, not just me. <br /><br />djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-27731786935844540522013-11-10T19:22:27.267-08:002013-11-10T19:22:27.267-08:00Dan, Interesting, thanks. A few thoughts:
On 1-2 ...Dan, Interesting, thanks. A few thoughts:<br /><br />On 1-2 week Santa Rosa Cycling Club tours, I started bringing a deep-cycle 12 v. marine battery and an inverter so that people could recharge all their devices (phones, cameras, Garmins, etc.). <br /><br />I always encouraged people to leave their phones turned off, because in remote areas, the phone cranks up its power to attempt to ping non-existent towers. IPhones that were left on needed to be recharged daily, while my Garmin 500 would last almost a week of 70-mile daily rides.<br /><br />On the last tour, some people used their iPhones for GPS bike apps, and had to leave their phones on, leading to a huge crowd of people wanting to recharge every night.<br /><br />I suspect part of the relatively good quality of iPhone GPS is that it might have more battery power available, in addition to bigger antenna. I know GPS is a power hog, because when I use my Garmin 500 with my powertap wheel on a trainer, and turn off GPS function, the battery lasts forever.<br /><br />Personally, I think the Garmin 500 is terrible from a ergonomic standpoint. I'm not sure mine is a great GPS unit, either. For awhile I used it while I ran laps on the local HS track (a tough test of a GPS unit, I admit) and in the tree-lines streets of the Berkeley Hills. The Garmin was all over the place--literally.<br /><br />I always use an old-fashioned wired bike computer alongside the Garmin. Leonard Zinn says he just puts his Garmin in his jersey pocket. They are very useful as "black boxes" in case of an accident, which is a main reason I continue to use it.<br /><br />It also really annoys me at how bad the Garmin is at providing ride information,especially splits, on the road without having to close out the current ride file. I'll take my old Cateye ATC 3000s any day. I have three, two have been working for almost 20 years, the third one finally died.<br /><br />So maybe Garmins, like low-end digital cameras, will be replaced by smart phones and their apps. Smart phones are becoming the digital equivalent of the Swiss Army knife.<br /><br />Michael Barnes<br />former (yet still appreciative) LKHC'erMichael Barneshttps://www.blogger.com/profile/06466641993175128509noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-33191907656712130292013-11-03T17:44:45.292-08:002013-11-03T17:44:45.292-08:00Robert: both the 500 and 800 default to smart reco...Robert: both the 500 and 800 default to smart recording unless power is being recorded. Power analysis software which calculates normalized power can be confused if data are not provided every second. Same deal with maximal power curves. So Garmin decided that power analysis required uniform sampling. But they didn't anticipate Strava, where position detection would also benefit from high resolution. They figured position was just to draw maps of where you'd been.djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-39286817949154725722013-11-03T17:42:34.802-08:002013-11-03T17:42:34.802-08:00Great comment emailed to me from Patrick, who does...<em>Great comment emailed to me from Patrick, who doesn't have a Google account:</em><br /><br />Fascinating analysis, Dan (as always)! Thanks so much. I have owned two Garmin 500s. The first was absolutely horrendous, dropping segments constantly. I ended up exchanging it at REI eventually and the replacement is also poor ("poor" compared to the 500s of some frequent ride companions) but barely serviceable.<br /><br />It so happens that my regular ride partner tracks her rides with a Garmin Forerunner 310XT. And the GPS tracking is consistently better and more accurate than any Garmin 500 in the group. When I dealt with Garmin customer service a number of times, they tried to convince me that all of the dropped and lost segments must be a product of "trees and cloud cover" which might be plausible except that the rider next to me using a 310XT never had any such problems...<br /><br />Garmin then informed me that the Forerunner 310XT uses a "totally different technology" to lock into satellites. I gather this is the "HotFix technology" which Garmin integrates into many of their automotive products. Per DC Rainmaker, "Yes, the FR310XT has a newer chip than the FR305, including hotfix technology for quicker pickups."<br /><br />Why the Edge 500 does not incorporate this technology too, I could only speculate. But I am guessing that the Forerunner is primarily intended as a trail running and lake swimming watch and needed a higher grade of GPS signal detection than Garmin believed the Edge series needed for cycling applications. Of course, the wide range of 500 results shown in your test (from horrendous to good) probably points most directly to quality control problems in their production more than anything else.<br /><br />Discussing these issues a bit with Paul Mach who developed the SNAP tool and now works for Strava, I also noted that a huge underlying problem with Strava segments is that many segments are originally drawn or created with a lot of inherent GPS drift. <br /><br />On a segment I cover almost every week (~4 miles), we tested this hypothesis a bit by creating as exactly parallel a new segment as possible to an old segment using the Forerunner 310XT data. The new segment timing pretty much exactly corresponds to stop watch timing, whereas the original one consistently gives times about 10-12 seconds longer than the new Strava segment or the wrist watch. I assume this is a function of GPS drift. Even though the times are longer for the same segment, Strava calculates the avg. speeds significantly higher for the original segment, presumably because it believes that more distance was covered in the longer amount of time.djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-18950101275769497162013-11-03T09:44:01.525-08:002013-11-03T09:44:01.525-08:00Very nice.
Do the 800's have a different def...Very nice. <br /><br />Do the 800's have a different default setting for "smart recording" than the 500's? Roberthttps://www.blogger.com/profile/08336037087994407943noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-44933072891573928142013-11-03T07:19:40.368-08:002013-11-03T07:19:40.368-08:00Tom: good idea. DC Rainmaker suggested the same t...Tom: good idea. DC Rainmaker suggested the same thing. I of course could determine that fairly easily.djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-66533878790215103972013-11-03T07:12:30.943-08:002013-11-03T07:12:30.943-08:00Can you follow up to ask how many of those Edge un...Can you follow up to ask how many of those Edge units are set on (not so) "Smart Recording"? I'm thinking that might have an effect.Tom Anhalthttps://www.blogger.com/profile/08175472546482777614noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-41922912373800385232013-11-02T19:18:54.123-07:002013-11-02T19:18:54.123-07:00I wonder if the rate of sampling is relevant on th...I wonder if the rate of sampling is relevant on the Garmins (ie. every second vs "smart" sampling). I'm guessing this isn't exposed in the data from Strava as they've already processed it.<br /><br />Re. logging in to scrape pages, I've had luck with CasperJS. It's handy for most sites being webkit, although I don't think it copes with HTML5 stuff such as local storage.Anonymoushttps://www.blogger.com/profile/11312344589433769197noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-57371584148716938182013-11-02T19:18:08.963-07:002013-11-02T19:18:08.963-07:00Thanks for the correction! iPhones in common circ...Thanks for the correction! iPhones in common circulation circa 2010 seemed to produce poor results. These were perhaps the iPhone 3G or 3GS (<a href="http://en.wikipedia.org/wiki/IPhone" rel="nofollow">Wikipedia</a>).djconnelhttps://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-46142434595310913772013-11-02T19:08:04.737-07:002013-11-02T19:08:04.737-07:00Hmmmm... I had a 1st-generation iPhone. There was ...Hmmmm... I had a 1st-generation iPhone. There was no GPS. None. <br /><br />So yes... it probably was infamous for poor GPS reception. :)<br /><br />I also think it's possible the Edge 500 has MORE room inside of it for an antenna than a recent iPhone. Space is extremely limited in there.<br /><br />Thanks for the analysis.U. Blockhttps://www.blogger.com/profile/05290390503533371933noreply@blogger.com