RunningAHEAD - Topic: 305 Distance v Map distance

The Plodder

posted: 10/4/2009 at 4:51 PM
modified: 10/4/2009 at 4:52 PM

As the proud owner of a new 305, i went for my first run tonight.

As I am on call tonight I just went running around the streets local to me. I have previously measured this route out at 3 miles, using the route mapper on RA.

Tonight using the Garmin the same run came out at a little over 2.7 miles.

i have read reports on here regarding races measuring long when using personal GPRS, but on such a small run, this is quite a margin of 'error'.

Haven't been back running that long, so now calling into question the length of the other routes i have run so far, will hopefully give them a try over the next week or so.

RunnerKSA

posted: 10/4/2009 at 5:47 PM

Were you in the city with tall buildings? That's the only thing that really throws my Garmin off. Otherwise, you can pretty much believe it!

Out there running since dinosaurs roamed the earth

iansyd

posted: 10/4/2009 at 5:50 PM

There are quite a few things that cause a difference in distance measurements GPS vs RA map. Have a look at the map trace generated by your GPS (by uploading to RA, Garmin training centre, or some other alternative) and compare it to your RA map. There will be something different.

My guess (and that's all it is) is one of the following:

You started running a little too soon after turning on your watch it had not "locked in" accurately
The route included some legs with poor visibility of the sky (eg tall buildings, underpasses, or tunnels)
you ran so fast that the sattelite's couldn't keep up

Well that last one is BS, but the other two can cause the watch to cut a few corners and give you a shorter route.

Running - cheaper than therapy

zoom-zoom

rectumdamnnearkilledem

posted: 10/4/2009 at 6:03 PM

I have also found that heavy tree cover and/or deep valleys can mess with it, too. During my last HM race there was at least one spot where my Garmin appears to have lost signal for a short stretch. I found that to happen during a trail relay in June, too. One area was on a steep hill with dense trees and tight switchbacks up the slope.

Getting the wind knocked out of you is the only way to

remind your lungs how much they like the taste of air.

~ Sarah Kay

nzrun

Loves the outdoors

posted: 10/4/2009 at 6:42 PM

I don't have a Garmin, but I have compared the RA maps with an accurately plotted course on Google Earth and found significant differences in some cases. On a particularly meandering route, RA maps measured much too long simply because it heads down the centre of each road. So because I was doing lots of right angle turns, it was adding 10m per turn simply because of the way the map plotted my course following the road. By the end of my run there was a 200m discrepancy. So check out Google Earth and see how that compares Smile

One day I decided I wanted to become a runner, so I did.

iansyd

posted: 10/4/2009 at 7:42 PM
modified: 10/5/2009 at 1:49 AM

Quote from nzrun on 10/4/2009 at 6:42 PM:

... RA maps measured much too long simply because it heads down the centre of each road.
....So check out Google Earth and see how that compares

RA maps track the centre of the road only if you want (because its easier than clicking every turn). Just unclick the "follow road" box when creating the course to allow you full control.

Running - cheaper than therapy

Teresadfp

One day at a time

posted: 10/4/2009 at 11:06 PM

I've checked my Garmin's reading at the end of races from 5K to HM, and found it to be within 2% every time.

bpurcell

posted: 10/5/2009 at 1:37 AM

Quote from iansyd on 10/4/2009 at 7:42 PM:

RA maps track the centre of the road only if you want (because its easier than clicking every turn). Just unclick the "follow road" box when creating the course to allow you full control.

I personally wish that was unchecked by default. I run a lot of non road paths, and it bugs me that I have to uncheck it every time.

http://briandpurcell.blogspot.com/

The Plodder

posted: 10/5/2009 at 5:05 AM

Thanks for responses

The route i took last night involved running up and down narrow streets that are close together and only a couple of hundred yards, so if the RA mapp adds 10m per turn that would explain the difference.

Will definteliy try the map upload in the future.

Will do a more circular route next time!!

BTW I did keep on for the extra 0.3 miles to make the 3 - that's commitment? LOL

Burnt Toast

posted: 10/5/2009 at 9:38 AM

You also need to look at the route as its plotted out by your Garmin. If you make alot of 90 degree turns (which it sounds like you did), you may not have had a data point taken right where you turned. That means that the Garmin route could take a 90 degree turn and chamber it by drawing a straight line across the corner. That could easily account for a shorter recorded route distance then you actually ran.

I /

____I ___/

I use the SportTracks software to look at and edit the route overlayed on satellite imagery to straighten out the plotted route. I find that the Garmin route is normally longer then the actual distance, but it can be shorter.

The pain that hurts the worse is the imagined pain. One of the most difficult arts of racing is learning to ignore the imagined pain and just live with the present pain (which is always bearable.) - Jeff

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305 Distance v Map distance - Confused (Read 637 times)