59 replies to this topic

[TheNatural]

Hey guys,

I just wanted to check and see if anyone had the same observation as me. I run with a Garmin 405, and I started it as soon as I ran over the first timing pad and exactly when I ran over the last and things just don't add up.

The total distance calculated by my watch for the entire run was 21.76km's. Did anyone else get this?

I was aiming for a 90min race and my watch tells me that I ran 88.44 after 21km. But over the distance of the course I ended up with 92.01. Did anyone else get a different reading?

Also, this is my second half so I'm not sure of most of the races out there, but did any of you experienced runners find this course particularly tough, lots of hills, etc.. For me it was a lot harder than the Blackmores last year.

Hope to hear from you guys :-)

Thanks,
Russell.

[Vurt]

it is the GPS signal bouncing all over the place due to the tall buildings. Mine was about 1km out at the 2km marker.

[TheLogicDump]

Hi Russell,

You will find that your Garmin will not read accurately on any race like this through the city. The Garmin will loose the signal through tunnels and throw off the measurements. Depending on the situation the Garmin will either over measure or under measure the distance run.

Tim

[SMCRoadRaceSeries]

Here we go again.

How about we put a sticky post at top so people can read how courses are measured (not by GPS) or just add the latest "is the course short? my garmin read xx:xx"

[Johnso]

I have to say though that my Garmin did read way over what it normally does for a half at 21.62. I run through most if that area all the time and its not usually out by that much. I put it down to the lost signal in the tunnel twice and the excessive dodging and weaving I had to perform after losing my starting spot when I had to go to the toilet with 15 mins until the gun

Edited by Johnso, 15 May 2011 - 01:46 PM.

[Rainlover]

SMCRoadRaceSeries, on 15 May 2011 - 01:29 PM, said:

Here we go again.

How about we put a sticky post at top so people can read how courses are measured (not by GPS) or just add the latest "is the course short? my garmin read xx:xx"

Here we go again....cynicism not required !!!!

[Action]

Three things...

first, I know who measured it and how it was done - it is 21.1186 kms long - absolutely no doubt (21.097k *1.001 short course correction factor - who is going to admit to running on the odd footpath?).

second, download your garmin to google earth or sport tracks or your software of choice and zoom in, right in, and see where the garmin thought you  ran.  You will find it got confused in the corkscrew, under the various overpasses, alongside the tall buildings (even in Hickson Rd) but wherever it was relatively clear sky it was damn close!  

third, mine gave me 21.62.  About what I expected given the race's location.

lastly, (yesI know I said 3), I am still mightily impressed by GPS technology.  Amazing what is on your wrist now.  Just stunning.

cheers

[SMCRoadRaceSeries]

Rainlover, on 15 May 2011 - 02:24 PM, said:

Here we go again....cynicism not required !!!!

So I gave a solution...have a permanent sticky thread to answer the question, so that people know how it is done and why their GPS' are inaccurate.

What is yours? A separate thread after every race???

[aDrain]

I suspect that this talk of GPS signals getting confused by buildings and tunnels is actually a conspiracy by iPod and other MP3 player makers to disguise the interference they cause to the natural radio and magnetic state of things.

Obviously the more iPod wearers the greater the effect and larger the individual discrepancies will be. Also why an iPhone app is never 100% accurate.

Edited by aDrain, 15 May 2011 - 03:06 PM.

[oxnardmontalvo]

Mine was about 21.6, but I figure the extra is the running around people and back and forth across the roads etc, it adds up over two hours. I have no doubt the true distance was spot on, and actually my Garmin measureed closer to the 21.1km than when I ran my last half, in Newcastle, which measured like 21.8km or something.

[Action]

aDrain, on 15 May 2011 - 03:05 PM, said:

I suspect that this talk of GPS signals getting confused by buildings and tunnels is actually a conspiracy by iPod and other MP3 player makers to disguise the interference they cause to the natural radio and magnetic state of things.

Obviously the more iPod wearers the greater the effect and larger the individual discrepancies will be. Also why an iPhone app is never 100% accurate.

implicate the ipods - obvious!  Love it.  Must link over the ipod thread - that should stir things up.

[fatboyslim]

GPSs generally only work when you can see the sky where the satelites are. I dont know if I was the only one but I couldnt see it in the tunnel. I only use my garmin as a guide for pace and a rough distance and a couple of hundred metres over 21 kms is rough enough for me. Awesome technology though.

[russell2pi]

Just a comment on ducking and weaving as an explanation for measured excess distance. (Who remember's Pythagorus' Theorem?)

Let's say you cross the whole width a 15-m wide roadway at a 45 degree angle - you've just done 21 m instead of 15 m, so 6 m extra, not 15 m extra as you might be inclined to think. Do it at shallower angle in the space of 50 m forward distance and you only cover 2 m extra to cross a 15 m road. Move 2 m across in 10 m forward to go round someone and again you've only added 20 cm to your distance!

Unless you're ducking and weaving like Mike Tyson, it's not going to add a huge amount to your distance.

[aDrain]

russell2pi, on 15 May 2011 - 03:37 PM, said:

Just a comment on ducking and weaving as an explanation for measured excess distance. (Who remember's Pythagorus' Theorem?)

Let's say you cross the whole width a 15-m wide roadway at a 45 degree angle - you've just done 21 m instead of 15 m, so 6 m extra, not 15 m extra as you might be inclined to think. Do it at shallower angle in the space of 50 m forward distance and you only cover 2 m extra to cross a 15 m road. Move 2 m across in 10 m forward to go round someone and again you've only added 20 cm to your distance!

Unless you're ducking and weaving like Mike Tyson, it's not going to add a huge amount to your distance.

Nah - easier to blame iPods

[russell2pi]

aDrain, on 15 May 2011 - 03:51 PM, said:

Nah - easier to blame iPods

Yeah... those !@*(& things give me asthma too!

[Johnso]

Maybe more to the point, the ducking and weaving means you probably can't run the race line but I see your point. It was probably my ipod.

[Action]

russell2pi, on 15 May 2011 - 03:37 PM, said:

Just a comment on ducking and weaving as an explanation for measured excess distance. (Who remember's Pythagorus' Theorem?)

Let's say you cross the whole width a 15-m wide roadway at a 45 degree angle - you've just done 21 m instead of 15 m, so 6 m extra, not 15 m extra as you might be inclined to think. Do it at shallower angle in the space of 50 m forward distance and you only cover 2 m extra to cross a 15 m road. Move 2 m across in 10 m forward to go round someone and again you've only added 20 cm to your distance!

Unless you're ducking and weaving like Mike Tyson, it's not going to add a huge amount to your distance.

exactly the same argument for the not yet mentioned hilly course making it longer.  Bugger all difference.  Gotta be the ipods - they must have robbed me of my hill running strength out of Mrs Macs Chair...

[brewer]

How off can a Garmin get?

Have a look at My race this morning. Zoom in on Sussex and MacQuarie Streets where the signal got a bit mixed.

[mgi11a]

TheNatural, on 15 May 2011 - 01:08 PM, said:

Hey guys,

I just wanted to check and see if anyone had the same observation as me. I run with a Garmin 405, and I started it as soon as I ran over the first timing pad and exactly when I ran over the last and things just don't add up.

The total distance calculated by my watch for the entire run was 21.76km's. Did anyone else get this?

I was aiming for a 90min race and my watch tells me that I ran 88.44 after 21km. But over the distance of the course I ended up with 92.01. Did anyone else get a different reading?

Also, this is my second half so I'm not sure of most of the races out there, but did any of you experienced runners find this course particularly tough, lots of hills, etc.. For me it was a lot harder than the Blackmores last year.

Hope to hear from you guys :-)

Thanks,
Russell.

Hey Russell don't worry too much about it, your not the first and you certainly won't be the last to ask this question of a race.
As explained it's more then likely an inaccuracy in the gps then in the course measurement.
Thats why it's a good thing to run your race on the course measure, turn auto lap off and take your splits at the km marks. At the end of the day the finish line will be where the course measurer puts it, not where your gps thinks it should be.
All that aside well done on a great time for just your 2nd 1/2.

Cheers

mgilla

[JBee]

I got 21.38km at the Canberra Half last month, and 21.30km today, both with my 410. Was aware of trying to stick to the racing line but pretty impossible on that course with those numbers... Still a great pacing & training tool though, as long as you know it's going to give you a slightly slower time / longer distance than you might think.

[vat]

At least you got a plot - I remember doing the event with the old Forerunner 201 back around '04 which completely lost signal once we got on to Pitt Street and pretty much gave up.  They've come a long way since then.

[WetWeek]

brewer, on 15 May 2011 - 04:39 PM, said:

How off can a Garmin get?

Have a look at My race this morning. Zoom in on Sussex and MacQuarie Streets where the signal got a bit mixed.

  That'hopeless!  You'd be way more accurate measuring your run with a piece of string and a Melways!

[Notamidlifecrisis]

I also felt there was something funny going on.  My 405 registered 21.2km, and it usually read a touch short.   To further complicate things, you lose satellite connection going through the Cahill tunnel.   I was 3sec ahead of my target pace going into the tunnel, and 1:15 ahead shortly after leaving the tunnel.   Both tend to indicate the course might have been a bit longer than the official 21.1.

[Action]

WetWeek, on 15 May 2011 - 06:18 PM, said:

  That'hopeless!  You'd be way more accurate measuring your run with a piece of string and a Melways!

can't help myself.... you would need a Sydways....

[WetWeek]

Action, on 15 May 2011 - 06:38 PM, said:

can't help myself.... you would need a Sydways....

LOL!  That would certainly help.

[Gento]

Off topic, but Regarding GPS - I had a friend's gps in the car (Garmin) tell us we were driving through Narabeen lake. They are great, but not 100% reliable.

As for blaming ipods, don't forget the aura of the elite runners - surely they give off some emp?

[Easy Tiger]

A cheat jumped in at the 17km mark, pretty sure his Garmin will come up short of 21.0975km's. He entered the race amongst the battle for top ten, on a positive for the ipod fans, he was considerate enough to have his volume turned down low enough so he could hear the protests from his 'rivals' and the abuse from the crowd.

[ChookLegsMonkeyBoy]

Gento, on 15 May 2011 - 06:52 PM, said:

Off topic, but Regarding GPS - I had a friend's gps in the car (Garmin) tell us we were driving through Narabeen lake. They are great, but not 100% reliable.

On the way home, whilst driving over the Harbour Bridge, my car's GPS had me heading through Sydney Harbour near Balmain towards Cockatoo Island.
It finally locked on to sufficient satellites to correctly place my position once I got to North Sydney. Makes the 500m error of my Garmin seem quite trivial!

[Jimmy4990]

At one point during km16, my 305 clocked me at 591km/ph or 00.06 m/p/km for those into pace. I also climbed over 400m & ran an extra kilometre. I will be using minutes & seconds next time as I thought my goal was achieved untill I looked at the clock 80.09. Happy with the run & new PB but I do feel let down by my Technology   as it is normally +/- less than 20 metres

[mgi11a]

brewer, on 15 May 2011 - 04:39 PM, said:

How off can a Garmin get?

Have a look at My race this morning. Zoom in on Sussex and MacQuarie Streets where the signal got a bit mixed.

Sure there's not a back room wine bar there that you may have accidently found your way into?

[AaronR]

No No, GPS's are dead accurate.
Today running through the tunnel I ran a 1'32" km! Yes I am awesome! You may all bow down to me

[fatboyslim]

AaronR, on 15 May 2011 - 07:50 PM, said:

No No, GPS's are dead accurate.
Today running through the tunnel I ran a 1'32" km! Yes I am awesome! You may all bow down to me

Can you train me please. Mr and Mrs Runhard are fast but you are way faster.

[Quinkin]

My Garmin returned 21.5. Not a bad margin for Garmin error over a half. Other certified HM courses giver varying Garmin results. The Hidden Half recorded 20.8. The Twlight Half is about 21.4.

[craigus]

AaronR, on 15 May 2011 - 07:50 PM, said:

No No, GPS's are dead accurate.
Today running through the tunnel I ran a 1'32" km! Yes I am awesome! You may all bow down to me

So that's why I couldn't keep up with you.  I must buy one of those fancy things.....

[GCRunner]

My 405 gave 21.56km. Interestingly, it was spot on at the 2km after the first corkscrew but over-estimated lap on lap after that. My maximum speeds are also all over the place (up to 60km/hr). As noted by other posters - it must be the buildings. It's spot on with plenty of open space and clear sky.

[Rainlover]

SMCRoadRaceSeries, on 15 May 2011 - 03:05 PM, said:

So I gave a solution...have a permanent sticky thread to answer the question, so that people know how it is done and why their GPS' are inaccurate.

What is yours? A separate thread after every race???

SMC - you offer no solutions. Not such a good idea nor fair to do this under the banner of the SMC. There is never any comment made by runners on this site that is not met without some sort of arrogance or sarcasm. With this, I have no further comment or interest in any response you may make. Comments from others have been constructive and helpful.

[PeterPlodder]

My Garmin Forerunner 310XT measured it as 21.90, but it always has a problem with tunnels so I wasn't surprised.

Next time, I might take up the suggestion above, of turning off the autolap and recording laps at the distance markers.

[superflake]

AaronR, on 15 May 2011 - 07:50 PM, said:

No No, GPS's are dead accurate.
Today running through the tunnel I ran a 1'32" km! Yes I am awesome! You may all bow down to me

Mine got stuck on 2:28 per k for about half a k. Thought I was david rudisha for a while. The buildings muck up the measurement. Mine read 21.81ks at the end. No wonder I was 1:30 slower than last year.

[JBee]

Rainlover, on 15 May 2011 - 10:01 PM, said:

SMC - you offer no solutions. Not such a good idea nor fair to do this under the banner of the SMC. There is never any comment made by runners on this site that is not met without some sort of arrogance or sarcasm. With this, I have no further comment or interest in any response you may make. Comments from others have been constructive and helpful.

totally agree. I've considered joining some of the SMC events but after seeing the sarcastic attitude shown in this thread there's no way I'd want to have anything to do with them. Surely this website is about help, support and advice - none of which is offered here. Gives SMC a very bad name - I suggest you get a seperate username if this is how you're going to carry on (or better still, keep your comments to yourself)

[Johnso]

jayrbee70, on 16 May 2011 - 07:18 AM, said:

totally agree. I've considered joining some of the SMC events but after seeing the sarcastic attitude shown in this thread there's no way I'd want to have anything to do with them. Surely this website is about help, support and advice - none of which is offered here. Gives SMC a very bad name - I suggest you get a seperate username if this is how you're going to carry on (or better still, keep your comments to yourself)

I agree too. I have exactly the same thoughts about SMC.

[Bellthorpe]

Rainlover, on 15 May 2011 - 10:01 PM, said:

SMCRoadRaceSeries said:

So I gave a solution...have a permanent sticky thread to answer the question, so that people know how it is done and why their GPS' are inaccurate.

What is yours? A separate thread after every race???
SMC - you offer no solutions. Not such a good idea nor fair to do this under the banner of the SMC. There is never any comment made by runners on this site that is not met without some sort of arrogance or sarcasm. With this, I have no further comment or interest in any response you may make. Comments from others have been constructive and helpful.

Are we reading the same post from SMC? If "have a permanent sticky thread to answer the question, so that people know how it is done and why their GPS' are inaccurate" is not an offer of a solution, what is it?


It sounds quite sensible to me.

[twosheds]

I dont understand why people get so upset about the same questions get asked over and over. You don't have to participate. People like the current dialogue as well as the answers they seek. If they just wanted answers to certain things they could just google and CR need no longer exist- Newer runners  want to interact with more experienced ones - not just read their old posts. So if it upsets you- dont  open the thread- easy.
For my 2 c on the current thread- even if your GPS was 100% accurate it should end up measuring the course long as the course measurement must be done on the shortest possible route- virtually impossible for anyone as part of the main "pack" to run.
twosheds

[HillsAths1]

When using my Garmin, I am always so happy with my times when they show me as running extra and getting a good time, I get really upset (well really only a little peeved) when the course is shown as short and a poor time. I think this is more of a reflection on how I am running rather than the accuracy of my watch.
Yes the GPS is sometimes inaccurate(for many reasons) however it is a great tool if used with thought and not just acceptance that it is always going to be 100% right.
If it shows you as running 3min km going uphill and you are generally a 4min runner, then is it really a stretch to think that perhaps something is a little out?

[Johnso]

SMCRoadRaceSeries, on 15 May 2011 - 01:29 PM, said:

Here we go again.

I guess not Bellthorpe

[TFive]

My 405 was 21.57 I figure with all the ducking and diving it's probably accurate. Not as bad as Tokyo Marathon when my Garmin gave a me a reading 45.87

[SMCRoadRaceSeries]

Bellthorpe, on 16 May 2011 - 07:48 AM, said:

Are we reading the same post from SMC? If "have a permanent sticky thread to answer the question, so that people know how it is done and why their GPS' are inaccurate" is not an offer of a solution, what is it?


It sounds quite sensible to me.

Thanks.  It's amazing how some people take things personally.

This is one of many recurring themes on CR where it would be very useful to have permanent 'stickies' or 'technical notes'. I would have thought that would be beneficial to newbies to click on it and say "ahh so that's why my GPS read xx:xx

As for SMC. Most of my SMC posts are made foir SMC related posts -as my sixfoot name is for 6ft topics- perhaps people will be boycotting that too?? Some of my posts relate to RD experience at SMC eg waterbags, IPOD usage and even course measurement, so the 'solution' comes from experience in that.
If what I said will result in SMC not having the eminent presence of rainlover and jayrbee, I will gladly step down from my roles there and look forward to these guys stepping in.

cheers

[JemWhyte]

I used a 405 for the first time on Sunday - the 2 times in the tunnel on cahill exp. accounted for my difference in actual time and moving time (bummer coz moving time gave me sub 90   .

Overall my garmin and the km markers 'flirted' with each other all race, sometimes under, sometimes over, sometimes perfectly in tune. At the finish line however, i stopped my watch and it read 21.124kms. I couldn't be more impressed.

Also - i found it funny when i loaded the data up to garmin connect and the map had me running over buildings, cutting across the grass and through the fountain in Hyde park etc.
view here http://connect.garmi...tivity/85684321

I think garmin and google might need to chat more...or perhaps they keep it as an inside source of humour.  

great day out

jemwhyte

[Waverider12]

SMCRoadRaceSeries, on 16 May 2011 - 10:05 AM, said:

Thanks.  It's amazing how some people take things personally.

This is one of many recurring themes on CR where it would be very useful to have permanent 'stickies' or 'technical notes'. I would have thought that would be beneficial to newbies to click on it and say "ahh so that's why my GPS read xx:xx

As for SMC. Most of my SMC posts are made foir SMC related posts -as my sixfoot name is for 6ft topics- perhaps people will be boycotting that too?? Some of my posts relate to RD experience at SMC eg waterbags, IPOD usage and even course measurement, so the 'solution' comes from experience in that.
If what I said will result in SMC not having the eminent presence of rainlover and jayrbee, I will gladly step down from my roles there and look forward to these guys stepping in.

cheers

Hi SMC, just a suggestion to avoid any future confusion about how the course is measured - why not add a brief description in all of the online and offline communications leading up to the race?

[Johnso]

SMCRoadRaceSeries, on 16 May 2011 - 10:05 AM, said:

As for SMC. Most of my SMC posts are made foir SMC related posts -as my sixfoot name is for 6ft topics- perhaps people will be boycotting that too??

Why is it that I could never imagine Wayne from the Blackmore's events talking like this?

[HillsAths1]

Johnso, on 16 May 2011 - 10:48 AM, said:

Why is it that I could never imagine Wayne from the Blackmore's events talking like this?

Perhaps because he does not organise SMC or 6ft?