Everyone is Digital Doping

Questions about bike hire abroad and everything light bike related. No off-topic chat please

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HammerTime2
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Joined: Thu May 04, 2006 4:43 pm
Location: Wherever there's a mountain beckoning to be climbed

by HammerTime2

http://spectrum.ieee.org/tech-talk/at-work/test-and-measurement/why_every_gps_overestimates_distance_traveled
GPS is overestimating distance traveled, therefore overestimating average speed.

Sleepless
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Joined: Sun Feb 23, 2014 7:58 pm
Location: Istanbul, TR

by Sleepless

I think that's why we still have speed sensors, no?

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russianbear
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Joined: Wed Apr 11, 2012 3:40 am

by russianbear

2% error? I'm fine with that. While statistically significant, it's not real life significant for me.

Nefarious86
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by Nefarious86

Not an issue if you ride to Power and track TSS ;)
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ross
Posts: 393
Joined: Mon Mar 14, 2011 10:59 am
Location: Oxfordshire UK

by ross

Sleepless wrote:I think that's why we still have speed sensors, no?


GPS is good at measuring speed at a constant pace (eg when you are driving on the freeway at 70 mph for example. It's not great at detecting short sharp accelerations and decelerations, and also the GPS signal can be blocked and interfered by high rise buildings and trees. The speed sensor is designed to mitigate those circumstances

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Tomstr
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by Tomstr

ross wrote:GPS is good at measuring speed at a constant pace (eg when you are driving on the freeway at 70 mph for example. It's not great at detecting short sharp accelerations and decelerations, and also the GPS signal can be blocked and interfered by high rise buildings and trees. The speed sensor is designed to mitigate those circumstances


Yes and no, the frequency of the GPS device is important here. If a Garmin or Mio would ping at 5Hz or 10hz like you see in racing cars the data would be a lot better (and higher volume!). Things like Garmin's corner skipping with mountainbiking tight hairpins will also be happening less. The interference of buildings and trees is another thing. That has more to do with the antenna in the device.
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CPongpanich
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Joined: Wed Nov 11, 2015 9:36 am
Location: Yorkshire, UK / Bangkok, Thailand

by CPongpanich

This is interesting. I used to be using Strava on a less expensive smartphone which did not have a very good GPS receptor. On Strava, almost every of my rides got about 10% increase in average speed and distance which is crazy.

KeepinitRIL
Posts: 6
Joined: Sun Dec 06, 2015 5:09 am

by KeepinitRIL

I have done multiple rides where I would Strava with my phone and use the Garmin as well, it depends on where you are, I had a really long ride, where the Garmin added 4 miles.
Meanwhile, on my short local rides(30 miles) Garmin would but short by .3 or .4 miles. On the short ride, Garmin would report 1800 ft of climb, while Strava would tell my 8400 ft of climbing.

Im not gonna lie, to get the climbing challenge, I used Strava on my phone.

jimborello
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Joined: Sun May 31, 2009 5:07 am

by jimborello

Yes, it is not a problem if you are riding power. But from what Ive seen mobile phones tend to overcalculate distances when compaired to gps units so maybe the roblem is worse in mobiles

petepeterson
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Location: 604

by petepeterson

Who cares about average speed?

Effort x duration

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djconnel
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by djconnel

This is only true if you use the raw position points and interpolate trajectory. Strava is more sophisticated than this. You can try it yourself -- download a GPX file, write a script to mine the position points, calculate the sum of distances between the points, and the result will substantially exceed what Strava reports for the distance.

On Strava vs Garmin altitude -- the result depends on whether you used the Garmin altitude numbers, which can be corrupted by water clogging the barometer port, or applied altitude correction with Strava, which can be poor in regions of large transverse slope, or worse, when bridges cross substantial drops.

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tinozee
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Joined: Wed Jun 01, 2011 7:53 am

by tinozee

I have enjoyed using iphone strava app and Garmin to compare. It is especially different with segments. The ios app will use way fewer points and gets a faster time in many cases. For example when the end of seg is at a road crossing and the actual garmin end point is a bit further out than the one ios strava is using. The garmin user gets hose cuz he has to brake at that point. I think it is because the seg creation tool does not snap to points. My explanation is not great, sorry. Try and you will see what I men.

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