Strava reliability

No problem!
No problem!

MattT53 wrote:Strava always

MattT53 wrote:

Strava always gives a lower avg speed than the data directly from my garmin. I assumed this was due to what im going to call gps drift (i.e when stood still the garmin reads 0.5 mph or so)?
Also, does anyone know how do you go about defining a known elevation for an edge 800? (i’m a bit technolically challenged!)

Matt,

Goto this website and navigate to the location that you want to predefined the elevation for. It will tell you (using your choice of NASA or OS data) exactly how high above sea level a given location is. Best to use a proper computer, rather than a phone or tablet for this website! http://www.osola.org.uk/elevations/

Once you know the elevation of your given location:
1) Goto the map screen on your Garmin and press the icon with the four arrows, to enter full screen mode.
2) Pan around and zoom out / in to find your chosen location? Once you’ve found it, zoom in to make your saved location as accurate as possible.
2) Tap at the precise place you want to define the elevation and a pin will drop in place on the display. If you mess up, just tap again and it’ll move.
3) at the top of the display you’ll see a little information box with the coordinates and elevation displayed (carry on even if the elevation is correct as you want to override the barometric sensor on the Garmin and ensure it’s always correct at the start of a ride – this only happens when you predefine).
4) Tap on the information box and you’ll get a new screen with 3 buttons along the bottom. The middle one is a little flag on an “x” a as in “x marks the spot”. Press it!
5) your Garmin will say something like “location saved as 001” a click ok.
6) A new screen will appear like before except the middle button is now a pencil – press this to enter edit mode to edit the location.
7) now you can change the name, the symbol it is displayed as on the map (think office block for work or little house for home) and crucially the correct elevation.
8) Scroll down to “change elevation” and select it.
9) Use the delete key top right to get rid of all the zeros and type in the correct elevation. You must fill all 5 spaces, so if your location is 45 metres above sea level, you should out 00045. Then press the green tick.

That’s it! Now whenever you start the Edge’s timer within 50 metres of that location it will automatically set the elevation to whatever you put in and then give much more accurate readings based on the barometric pressure. It’s like automatically calibrating it every time you start a ride.

You’ll also find that you can navigate to your saved locations easily by going to the “where to” menu and selecting “locations”. Great if you’re half way round a route and decide for some reason that you just need the quickest route home possible etc and want to use your edge as a sat nav!

Garmin connect has a feature
Garmin connect has a feature to enable elevation corrections, which I think are taken from proper maps. The feature is on the bottom right of each individual ride. Not that you should obsess too much, it’s only a guide and your legs will certainly tell you when you’ve climbed enough!

Dave Atkinson wrote:the

Dave Atkinson wrote:

the iphone 4 uses a Broadcom BCM4750IUB8 single-chip GPS receiver. so yes, it does have proper GPS

not all chipsets (and not all chips of the same type) are equally capable. I’ve had two HTC One X handsets and the GPS tracking on the first was noticeably better than on the second

I checked – you’re quite correct, although it appears to be supplemented by cellphone signal triangulation and wi-fi networks. I assume the GPS chip alone isn’t as good as others, otherwise why bother with the other stuff etc.

If I remember correctly, the
If I remember correctly, the iphone doesn’t actually have GPS – it triangulates it’s position based on cellphone towers*, aided by the location of local wifi networks**. I’m not sure if altitude is calculated based on the same triangulation (that sounds flaky) or a co-ordinates lookup of your location against an OS map with altitude data derived from there.

Contrast all that with a Garmin, for example, which is a ‘true’ GPS device relying on satellite positioning.

Over a 100km ride, my phone and Garmin differ by maybe 1km distance, so not a big deal. I’m not sure about difference in ascent.

Overall, I think the phone app is definitely useful. If I have the battery life, I record on both, then if I’m in a rush later, upload from the phone (easier) rather than booting the laptop and hooking up the GPS, which is a bit of a faff.

* = If a phone has ‘proper’ GPS, then in theory you can still navigate when in aircraft mode (i.e. no phone or data signals), but the iphone 4 will do no such thing.
** = This may have changed for the iphone 5 when maps data switched from google to Apple.

I got this phone ages ago, so I may be talking bollocks, but hopefully not!

Like others have said, I
Like others have said, I wouldn’t trust GPS alone for accurate speed or distance data. If you want proper accuracy, combine a Garmin with a speed / cadence sensor that uses the size of your wheel to know EXACTLY how far and fast you have travelled.

As for elevation, that’s far more troublesome. Elevation calculated by GPS is very haphazard for a host of very complicated reasons. If you can afford a Garmin with a barometric pressure sensor, you can find out the correct height above sea level for places you start your rides from, such as home, office etc and pre-define them in your Garmin. The elevation readings it gives based on changes in atmospheric pressure as you climb or descend are then pretty accurate – certainly more accurate than GPS.

If you consult Strava’s help pages you’ll discover that they use data submitted from Edge 800 users over smartphones to correct their data as it is much more accurate.

To summarise, smartphone GPS not great, Garmin GPS better, Garmin GPS with speed / cadence as good as you can get, but none of this tech will be 100% accurate for elevation.

There’s a good blog from @StravaTips comparing smartphones to dedicated GPS linked below – I’ve never regretted investing in an Edge 800!

http://www.scarletfire.co.uk/2012/07/iphone-gps-fail/