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Old 04-05-2013, 10:57 AM   #1 (permalink)
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Default Speed board/ski apps inaccurate? why?

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Originally Posted by poutanen View Post
How many times do I have to say it?!? THE SKI APPS ARE NOT ACCURATE! Comparing your top speeds is useless that way...
Was going to post this in original thread I found it, but I would've been risking a thread "hiJack accusation",

So I decided a new post!

I'm not interested so much in everyone telling me "Their App IS accurate!" Or their app is ALWAYS OFF etc.

I'm more interested to know why would that be so. Give some evidence or explanation for why that would be so!

I ask because although I don't expect them to be spot on, I usually rely on them being within 3-5 mph. give or take! The phone apps I use for MTB'ing seem to line up with about that degree of accuracy when compared to the wired speedo/odo on my bike!

They are the same class of application on the same general sorts of terrain, relatively remote locations, elevation, trees & tight turns, especially for you "Glades riders"? So why would the snow sports dedicated apps be inaccurate for boarding? Just curious, as I logged almost 50 mph this season. (...only reasonably sure it was at or just above 45 mph, but still, a personal best for me!!! I'd like to feel good about my "Bragging Rights!")
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Old 04-05-2013, 11:08 AM   #2 (permalink)
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Just finished reading the same thread on helmets and was gonna start this thread as well.
So why are ski tracking apps not accurate? (I haven't used one yet...)
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Old 04-05-2013, 11:45 AM   #3 (permalink)
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I am interested in this claim as well. After the first thred of "they dont work" i turned it on and drove back from Golden. Tracked my speed in my car almost spot on climbing hills, going down hills, correct elevation etc.
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Old 04-05-2013, 12:04 PM   #4 (permalink)
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Me too. I tested mine in a car also. Alpine Relay and DotFreeRide.
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Old 04-05-2013, 01:01 PM   #5 (permalink)
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It has to do with how they clock or log latitude and longitude coordinates. The more it logs GPS the more accurate the app. So, for an example, it pings every second it collects less data vs collecting every half a second. It tracks the GPS changes. So if I am in spot A and spot A has Long/Lat of this, when I am on B it has Long/Lat this. It tracks the time from A-B and it gives your speed. So when it pings the GPS this second on A and the next second it pings and you are B, it calculates it took 1 second to go from A-B so this is your speed. Now take the same example but use the half a second ping and it is way more accurate. So you ask why are the apps not all using the half second vs the 1 second? Battery. For a true accurate reading it would have to be a constant ping and that would kill your phone very quickly on battery.

Edit: I also forgot to add new or old phone or even what kind of phone. Older phones use older GPS chips. It boils down to how accurate (with-in feet) the GPS chip tracks. Older phones (or older chips) have less accurate tracking. You hear some GPS can find something within 10 feet. That would be less accurate of one that could track to 1 foot. Some are less some are more. The less distance of tracking the more accurate.

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Old 04-05-2013, 02:29 PM   #6 (permalink)
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Quote:
Originally Posted by kungfulu View Post
It has to do with how they clock or log latitude and longitude coordinates. ... an example, it pings every second it collects less data vs collecting every half a second.

... So you ask why are the apps not all using the half second vs the 1 second? Battery. For a true accurate reading it would have to be a constant ping and that would kill your phone very quickly on battery.
Ok, I get all that. As I mentioned in op, I never took any reading of my max. speed to b 100% spot on. I always assumed that any logged speed would likely b +\- a few mph. So I suppose the argument being made by detractors of these apps. Are the flat out claims of top speed without acknowledging THAT discrepancy?

Or are people claiming that these apps. are unreliable and inconsitantly inaccurate enough that ANY given speed is questionable?
Additionally, that still doesn't address my observation that similar apps used when I ride my MTB seem to B reasonably close to the milage & mph's logged with my bike mounted odometer! Again, usually anywhere within 3-5 mph. Any time I've encountered larger variences than that, they can usually b traced to signal loss or interference.

That level of accuracy is good enough for me to be reasonably confidant that I'm not making wildly inflated, bullshit claims for my snowboarding speeds. Are we arguing about split hairs here?
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Old 04-05-2013, 02:43 PM   #7 (permalink)
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Quote:
Originally Posted by chomps1211 View Post
Ok, I get all that. As I mentioned in op, I never took any reading of my max. speed to b 100% spot on. I always assumed that any logged speed would likely b +\- a few mph. So I suppose the argument being made by detractors of these apps. Are the flat out claims of top speed without acknowledging THAT discrepancy?

Or are people claiming that these apps. are unreliable and inconsitantly inaccurate enough that ANY given speed is questionable?
Additionally, that still doesn't address my observation that similar apps used when I ride my MTB seem to B reasonably close to the milage & mph's logged with my bike mounted odometer! Again, usually anywhere within 3-5 mph. Any time I've encountered larger variences than that, they can usually b traced to signal loss or interference.

That level of accuracy is good enough for me to be reasonably confidant that I'm not making wildly inflated, bullshit claims for my snowboarding speeds. Are we arguing about split hairs here?
I don't think they are inconsistently inaccurate. I think they are consistently accurate for how it is being logged. To your point of signal drop...that could be a huge factor in the results, solar flares can alter GPS readings…the list goes on. Even a half a second drop of not logging would throw the math off of how these track and would change the +/- big time. Each app creator uses a different algorithm based off of how they are tracking and how they built the app. You could take 3 different apps, load them on 3 iPhones and throw all three in a backpack, bomb down the mountain and when you pulled them out, they would probably all have a different number. The closest you could get to the real number is using the same app on the same phone over and over and that is because it would use the same way of collecting over and over.
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Old 04-05-2013, 02:57 PM   #8 (permalink)
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I tracked myself with apps for a couple years, various apps and various phones. My top speeds (after correction) were consistently anywhere from 100-130 kph each day.

I bought a Garmin GPS watch this year (after losing a phone on the hill) and was expecting similar results. My boarding hasn't changed, in fact I'm likely going FASTER as I'm used to the mountains more this year, but the top speeds have gone down to the 70 kph range at Fernie and Lake Louise (more off piste), and the mid-80 kph range at Nakiska (groomer bombing/hard carving).

The other thing is, my max speeds used to fluctuate by 20 kph a day at the same hills. Now it's very consistent. All my max speeds since changing to the watch (about 30 on hill days ago) have been within approx 15 kph over ALL the hills.

Next time I'm out, I'll take a smartphone with the app and run the GPS watch at the same time.

Overall distance will be reasonably close, although the apps don't pick up carving. Max speed for the day is just so random that looking at an app and saying things like "my max speed is higher than yours because _____" just doesn't make sense.

The apps are fun, it's a great way to push yourself for longer distance and vert each day, just ignore the max speed readout. It shouldn't even be there...
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Old 04-05-2013, 03:13 PM   #9 (permalink)
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Poutanen, just curious which GPS watch you are using and do you know how it is logging coordinates? 1 sec. or 1/2 sec. intervals. Or do dedicated GPS receivers handle things entirely different than phone app GPS does?

Looking to school my ignorance here,..
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Old 04-05-2013, 03:25 PM   #10 (permalink)
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Quote:
Originally Posted by chomps1211 View Post
Poutanen, just curious which GPS watch you are using and do you know how it is logging coordinates? 1 sec. or 1/2 sec. intervals. Or do dedicated GPS receivers handle things entirely different than phone app GPS does?

Looking to school my ignorance here,..
It's a Garmin Forerunner 410, and it doesn't have a set interval for logging. They claim it has a "smart interval" that decides when to log based on calculations.

From what I've read, the intervals can be anywhere from 1/2 a second to 5 seconds or so.

For what it's worth, the apps I used recorded raw GPS data from the phone at intervals that I told it to, and I uploaded that data to Garmins website, so I'm comparing apples to apples as far as how the data is interpreted after it's recorded.
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