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GPS vs SDM Devices

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  • Jim Adams
    (ED NOTE: This is a digest version of a rather long thread from DRS regarding various speed/distance measuring devices. The discussion centers around GPS
    Message 1 of 1 , Jan 2, 2006
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      (ED NOTE: This is a digest version of a rather long thread from DRS regarding various speed/distance measuring devices. The discussion centers around GPS units (primarily Garmin and Timex) and SDM units from Nike and Polar. It is long, but worth reading if you are contemplating buying one of these devices.)

      From: Jim Adams <jim@...>
      Subject: GPS v. Speed/Distance Unit?

      EB inquires:

      > I am in the market for a "person-based" measuring device. I would like
      > some
      > help deciding between a Forerunner 201 and a speed/distance unit, but I
      > don't know what. Timex Body Link, maybe?
      >
      > Does anyone have experience with using both a GPS running device and a
      > speed/distance thingie? Outside of price, pros. cons?

      The Nike SDM systems use a technology that can best be described briefly as
      the same force measuring technology that activates air bag systems in
      automobiles upon impact. Roy Benson himself told me that most of them are
      97% accurate right out of the box, and can be calibrated to the individual
      runner on a track. The devices are sensitive enough to that someone wanting
      complete accuracy needs to log the settings on different types of shoes
      (trainers vs racing flats, etc). They range from $100 units that just fit
      on the shoe to $400 units that include heart rate monitors, computer
      download interfaces (Windows, not MAC) and so forth.

      The GPS systems depend on obtaining and maintaining satellite signals. This
      can be a problem in deep woods, mountainous areas (canyons and valleys) and
      city with large buildings. Also, sometimes around military bases for a
      different reason altogether. If you lose the signal, the devices may stop
      recording for that time, and may shut down altogether if the signal is gone
      long enough.

      The GPS works on all modes of transportation - bikes, boats, vehicles, etc.,
      as long as it has contact with the satellites. The SDM system isn't
      effective if it isn't measuring your footstrike.

      I prefer the GPS simply because I can get on a bike on go measure race
      courses with it, even if they aren't certified. One advantage of doing it
      that way is that all those runners wearing a GPS during the race don't
      criticize the course length afterwards!

      Regards from Baltimore,

      Jima
      ------------------------------
      Date: Wed, 28 Dec 2005 14:23:12 -0800
      From: Larry James <horizontal_velocity@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      Speaking of GPS devices...Over the weekend I used my recently purchased
      Forerunner 201 for the first time. I can't compare it to a
      speed/distance unit, however, I do wonder about the accuracy of the
      distance measured as compared to my car odometer and my bike computer.
      All 3 of these measuring devices gave slightly different numbers for
      the same route.

      Nonetheless on the accuracy of the distance measurement, I find the
      Forerunner easy to use and comfortable to wear while on the roads. In
      fact, on yesterday's walk/run I wore my regular watch, my HRM wrist
      receiver, and the Forerunner. :) A bit overkill I know but I just
      wanted to see how it all felt.

      I know you didn't ask for all the anecdotal info but I wanted share
      anyhow.

      larry in phoenix, az
      :-)
      ...orn: 5.01 miles in 81 minutes of mostly walking and some running
      yesterday morning.
      ------------------------------
      Date: Wed, 28 Dec 2005 17:17:26 -0700
      From: Benji Durden <benjid@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      > Speaking of GPS devices...Over the weekend I used my recently purchased
      > Forerunner 201 for the first time. I can't compare it to a
      > speed/distance unit, however, I do wonder about the accuracy of the
      > distance measured as compared to my car odometer and my bike computer.
      > All 3 of these measuring devices gave slightly different numbers for
      > the same route.

      All three approaches give readings that are gong to be different for
      different reasons on different courses.

      I certify courses and train with a professional surveyor who wears a
      Forerunner 201 on most of his runs and he and I have discussed this at
      length. The car odometer is usually the least accurate. You don't know how
      it was calibrated or which wheel is the measuring wheel wheel. If your
      course has any turns, you are going to be off if the outside tire is where
      the measuring down even if the odometer is really accurately calibrated
      (which is very seldom the case). The Forerunner has inherent error that
      involves things like loosing and regaining the GPS signal. It extrapolates
      when that happens and does a pretty good job, but we have seen 6 Forerunners
      on the same day, on the same 3 mile certified course vary from 2.9 to 3.1
      miles. Good for log books, but not acceptable for course measurement. The
      bike computer can be a very good way to measure a course if you want to
      spend some time calibrating it. You will need to get a steel tape and a
      friend and measure a very straight line at least 400 meters long (a friend
      with a surveying total station will work too). That dome, you ride the
      "check course" several times adjusting you bike computer till it agrees with
      the know distance. Air pressure, tire pressure and temperature will case
      errors in your result, but they are small enough for the most part. Course
      measure with this method aren't likely to be more than 50 meters off in a a
      5K if you are careful in riding the tangents. To get any better, you would
      need to by a "jones counter" and follow the course certification guidelines.


      From Jima:

      > I prefer the GPS simply because I can get on a bike on go measure race
      > courses with it, even if they aren't certified. One advantage of doing it
      > that way is that all those runners wearing a GPS during the race don't
      > criticize the course length afterwards!

      On the GPS versus certification; I measured the new Bolder Boulder course
      this year and between my 2 rides I was about 2 meters different over the
      10K. After the race 3-4 people called to complain that the new course was
      200 meters long because that is what their Forerunners or Timex units or
      whatever said. I noted that with all of the turns it was unlikely they ran
      the course as tightly as I road it. It would have been obvious to the front
      runners that their times were 35-40 seconds off as well. GPS units are nice
      if you need a tighter log book, but they don't measure perfectly.

      bd

      Benji Durden
      benjid@...
      ------------------------------
      Date: Wed, 28 Dec 2005 19:49:08 -0700
      From: Tyler Bronder <tbronder@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      I've been using the Forerunner 301 for almost a year now, and for the most
      part it's excellent. The HRM on it is barely functional, but I didn't
      intend to use it so that's not a negative in my book. I do pretty much all
      my running on roads and rail conversion trails, so losing GPS reception has
      never been an issue with me. It does tend to report a lot of strange jumps
      in elevation, though you can use the motionbased.com site to match your
      location with USGS elevation data to correct.

      The USB port on the device has been troublesome, however. It's on the back
      side of the unit, and it appears that sweat is getting through the rubber
      covering and make the connection flakey. An extra piece of electrical tape
      over the cover should do the trick, without any discomfort. You might want
      to also look into the quick-release wrist band they sell, which would move
      the unit away from direct contact from the wrist.

      Sadly, I don't know anybody with the Nike foot pods or a Timex bodylink, so
      I can't do any form of comparison. But the Forerunner gets my
      recommendation. I only wish Garmin would make a Forerunner with the
      SiRFStar chip, which promises much better reception (they have a bike unit
      with it, but I guess us runners just aren't cool enough for one).

      Tyler
      ------------------------------
      Date: Wed, 28 Dec 2005 19:12:24 -0800
      From: Karl Watanabe <karlw2000@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      A few years ago, I too was in the market for a 'speed/distance' device and was about to get a running GPS system when Kathy bought me a Nike watch with the speed pod. I couldn't believe something stuck to my shoe would be very accurate, but once calibrated on a track, it was incredibly accurate and I could run on any surface and through the hills with lots of trees without any problems of losing satellite contact. I think Steve Patt tried the Nike system and had a few good things to say as well.

      Anyway, after my years of little or no running, I hadn't used it at all lately, but then Kathy just bought me a new Nike model with the HRM and speed pod. This is one incredible system that uploads all workouts without wires to our computer and will graphs HR/distance or time or HRM + Pace/distance or time. In fact, there are 6 different graphs available.

      I went to a track yesterday to calibrate the system and it was within 0.01 mile as I jogged 2 miles after calibration. I'm not a big believer in HRM's, but it is still cool to see my HR/speed or distance even if I don't plan to train by HR. This morning, I rowed 4000meters in 19 minutes with an averge HR of 130bpm and then went out for 3 easy miles at near 150bpm. It goes to show my months or rowing was indeed considered my 'easy' recovery days based on HR because if I tried to run at 130bpm, it would feel like a fast walk.

      I haven't been too impressed with GPS units due to lost contact in trees, and I also believe they are inaccurate when doing lots of turns. George Parrott once ran on my Fremont 2 mile lake loop when I estimated to be 2.1 miles and was sorta confirmed using my Nike system, but his GPS said it was 1.9 miles which I'm sure was short...probably due to lots of turns which I understand can cause shorter distances by GPS since it doesn't have the distance resolution to catch the turns.

      ORN: As said, 4000m rowing, and 3 miles in my company park.

      regards,
      Karl Watanabe
      Santa Clara, CA. USA
      ------------------------------
      Date: Thu, 29 Dec 2005 08:44:07 -0500
      From: "Neil L. Cook (Personal)" <Neil.L.Cook@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      Benji,
      >
      > To get any better, you would need to by
      > a "jones counter" and follow the course certification guidelines.
      >
      Are they still available? I owned one, mounted on my old, old bike, that I
      purchased from Clain Jones himself. Bill Noel used it to measure and
      certify all the NYRRC courses back in the day. I still have Ted Corbett's
      original course certification standards.

      nlc
      This e-mail has been scanned by an old runner and is assumed to be free of
      junk miles.
      ------------------------------------------------------------------------
      Neil L. Cook
      SLB Coaching & Training Systems
      Asphalt Green Triathlon Training Institute
      http://www.slb-coaching.com
      http://www.agtri.com
      neil.l.cook@...
      coach@...
      ncook@...
      coach@...
      New York City

      212-472-9281 or 917-575-1901 or 212-369-8890 x268
      For me Frailty is a lot harder to bear than dying.
      A Sweet Lightning Bolt Production
      ------------------------------------------------------------------------
      Date: Thu, 29 Dec 2005 07:03:52 -0800
      From: Karl Watanabe <karlw2000@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      One more thing about the Nike SDM with the HRM and speed pod...

      I had been in backchannel contact with Dave Cooper who has the Timex HRM and he said the HRM isn't linked to the splits because the data unit is separate. I have always loved the splits feature of the Nike Triax watches as well as the ability to save different workouts.

      When you hit the lap button on the Nike, it stores distance and HR along with the time splits. Upon manual recall of the data, it will give average HR for each split. I was able to store 4 different workouts on my Tuesday track calibration day and I get graphs for each workout and sampled data (not instantaneous) of both HR and speed during the run with markers showing when I hit the lap button.

      Downloading the data is simple as can be so I just need to be close the wireless data pod when I turn on the application and click on a 'sync' button. So no USB port to worry about like my MP3 players that eventually go bad due to corrosion from sweat getting into the system.

      Also, all the batteries are easily replaced on the watch, HR strap, and speed pod so you don't have to send the units back to the factory. Even my old trusty NIke Triax watch had to be sent to a professional for battery replacement this month.

      I'm going to the track again today for a 'real' workout and will report back my results later. If anyone wants a GIF file of the graphs, let me know and I will upload them to my web site for easy downloading.

      regards,
      Karl Watanabe
      ------------------------------
      Date: Thu, 29 Dec 2005 11:15:09 -0500
      From: Paul Loucks <loucksap@...>
      Subject: Current limitations of US GPS units

      Good morning...

      There was an interesting article in my local paper this a.m., as
      syndicated from the Washington Post. It dealt with the European
      Union's newly launched Galileo global positioning system created at a
      cost of 4.5 billion dollars. It was launched yesterday, December 28,
      by a Russian Soyuz rocket. Galileo will be able to provide accuracy
      for Europeans down to a yard -- yes, that's 36 inches! Such accuracy
      is currently unavailable on the U.S. GPS satellite system -- the
      civilian version of which is good only down to 16 feet. That's the
      limit of what WE now have available for our use here.

      Galileo was produced after considerable political bickering with the
      US. End result? The Europeans wanted freedom from our existing,
      limited single system simply because the US has the capability of
      turning it off over Northern Europe. In other words, reception in
      Northern Europe generally sucks. Also, the Pentagon argued back that
      Galileo will interfere with its military tracking systems. Hopefully,
      the future will bring greater cooperation and link these two separate
      networks for everyone's gain.

      At any rate, what is currently available here in the US -- to us as
      civilians -- is now inferior to Galileo. The US GPS military version
      is reported to be nearly as accurate as Galileo but our government is
      not saying specifically. The US is, further, working on updating its
      systems, both the military and civilian modes.

      But that's enough about the newspaper report.

      From my own personal experience (I own a Garmin GPS V model), I
      experience difficulty in heavily forested areas and when blocked by
      mountains. This is due to the existing configuration of satellites
      over and around me. If my signal, i.e., one of the several satellites
      hovering about me happens to be low on the horizon at a given moment,
      I will lose accuracy or temporarily receive no signal whatsoever. It
      varies, of course, from hour to hour. I find that some days are
      better than others.

      My only other comment, given existing political tensions and
      technical progress here in the US, is to make sure that ANY GPS
      device you purchase is WAA-enabled. This will maximize your
      reception and bring you down to the requisite existing standard here
      of 16 feet. Otherwise you're looking at 35 feet or more. The WAA
      technology comes on better grade systems, BTW, don't know if it is
      prevalent on the devices that runners use. I purchased mine for
      kayaking in open water and mountain climbing. It's also great for
      getting me to where I'm going in my car. I love it.

      For those of you discussing the merits of GPS devices for use in
      measuring race distances, there are obvious limitations, especially
      if you don't own a WAA-enabled device. For everyday approximations,
      however, all GPS devices are fun and helpful.

      My two cents...

      Paul in Potsdam
      ------------------------------------------------------------------------
      Date: Thu, 29 Dec 2005 09:04:45 -0500
      From: "Neil L. Cook (Personal)" <Neil.L.Cook@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      For running purposes, or as Benji said "running log" purposes, I find the
      Polar 625x to be the best choice. Out of the box it is over 95% accurate,
      and if you calibrate it, it is even better. I also have the Forerunner 201
      and have stopped using it - in the city, even in Central Park, I lose signal
      too often to make it useful. In open spaces it is much better.

      The Polar accumulates more information, downloading to a computer is easy
      and their software is great for analyzing heart rate, elevation, speed,
      distance data. There are a number of other software packages - TAD from
      Stevens Creek (Steve Platt, Dead Runner), Ultra Coach and PC Coach among
      others. I've used them all, but found my own spreadsheet the best for
      gathering numbers and crunching them - there are a number of spreadsheets
      from Dead Runners - David Hays, Allan Rube' and others.

      But, for devices for collecting workout information the Polar 625x is by far
      the best on the market. You can switch modes from running (distance) to
      cycling (distance & cadence) to nothing (just HR and time) with the push of
      a button.

      nlc
      This e-mail has been scanned by an old runner and is assumed to be free of
      junk miles.
      ------------------------------------------------------------------------
      Neil L. Cook
      SLB Coaching & Training Systems
      ------------------------------
      Date: Fri, 30 Dec 2005 02:18:38 -0500
      From: CincyKev <kclenden@...>
      Subject: Re: Current limitations of US GPS units

      Paul in Potsdam said:
      > It dealt with the European
      > Union's newly launched Galileo global positioning system created at a
      > cost of 4.5 billion dollars. It was launched yesterday, December 28,
      > by a Russian Soyuz rocket.

      Actually, only one satellite in the system was launched. The next one is
      slated to go up in the spring. It won't be until 2007 that they have enough
      (four) satellites up to allow for accurate triangulation.

      > Galileo was produced after considerable political bickering with the
      > US. End result? The Europeans wanted freedom from our existing,
      > limited single system simply because the US has the capability of
      > turning it off over Northern Europe. In other words, reception in
      > Northern Europe generally sucks.

      The fact that the US can turn the system off at any time does concern the
      Europeans, but that's not the reason that GPS signals in Northern Europe are
      substandard. To get a good location measurement, you need at least four
      satellites above the horizon. The satellites in the US GPS are in orbits
      that were not optimized for Northern Europe, so there aren't always enough
      satellites above the horizon, and clear of other obstacles like trees and
      buildings, to provide a good location fix.

      > Also, the Pentagon argued back that
      > Galileo will interfere with its military tracking systems. Hopefully,
      > the future will bring greater cooperation and link these two separate
      > networks for everyone's gain.

      Actually, once the Europeans made it clear to the US that they were going
      forward with the Galileo system, there has been good cooperation. Both
      sides sat down and worked out the protocols and specifications for Galileo
      and the next generation of US GPS so that they could coexist peacefully in
      the skies above. Manufactures have already indicated that they will build
      receivers that can work with either one, or both of the systems. You can
      expect to see those receivers start appearing in 2008.

      > At any rate, what is currently available here in the US -- to us as
      > civilians -- is now inferior to Galileo.

      Actually what we have available here in the US is far superior to Galileo at
      the moment. As noted above, it won't be until 2007 that there are enough
      Galileo satellites in orbit to give accurate measurements, and that will
      only happen when they are all above the horizon at the same time. It will
      be even more years before there are enough Galileo satellites in orbit to
      insure that there are always at least four satellites above the horizon at
      the same time.

      [snip]

      The next version of the US GPS will have accuracy comparable to Galileo. It
      will also have a stronger signal that will not be blocked by trees. I
      haven't recently seen estimates of when it will be operational, but the last
      few "backup" satellites that have been launched for the existing US GPS
      actually have the capability to be used with the next generation system, so
      I expect it will be operational before or concurrently with Galileo.

      CincyKev
      ------------------------------
      Date: Fri, 30 Dec 2005 08:57:42 -0500
      From: Paul Loucks <loucksap@...>
      Subject: Re: Current limitations of US GPS units

      Hi Kevin,

      Thanks for the update. My local newspaper gave only an abbreviated
      account. I suppose I could have checked out the matter a bit more --
      as you obviously did -- before posting...

      Regardless, since you are the only responder, I doubt if anyone else
      really much cared. :-)

      Mostly, GPS owners on DRS like to whine about the inaccuracy of their
      personal receivers. The point, of course, is that the performance of
      their receivers is completely dependent upon the global positioning
      system itself -- and that would be the US system -- the only game in
      town until 2007 or 2008 and, for a variety of reasons, poorly tuned
      for Europe .

      I have a wonderful, very readable book explaining GPS and how to make
      the most of it. If this is one of your interests, I recommend it
      fully. Actually, it's way more exhaustive than I personally care
      about.

      Letham, Lawrence. "GPS Made Easy: Using Global Positioning Systems in
      the Outdoors." (Seattle: Mountaineers, 4th edition, 2003).

      Carry on...

      Paul in Potsdam
      ------------------------------
      Date: Fri, 30 Dec 2005 11:49:56 -0500
      From: Fat Charlie the Archangel <jpuckett@...>
      Subject: Re: Current limitations of US GPS units

      Paul in Potsdam expresses a sentiment that many share, but is inaccurate -

      >Regardless, since you are the only responder, I doubt if anyone else
      >really much cared. :-)

      Oh, no! I really do care about the development of GPS stuff - and purely
      from a user standpoint. I just didn't know anything about Galileo, and I
      don't have any problem with the current setup.

      Canyons in Utah often killed my signal, but I don't remember any trouble
      with trees - and I don't think they'll come up with a signal strong enough
      to go through granite mountains :)

      ...and here in Arizona, I've not had any problem with my GPS except for
      one run, with Bob Spencer, downtown in the tall buildings. So I don't mind
      a bit if they leave it alone, as far as my running is concerned, but if it
      gets more accurate, that's all to the good - however, since I'm not
      running up switchbacks like I was in Park City, accuracy isn't as much of
      an issue either.

      Now, if they could come up with a GPS that would heal my shin splint...

      But the fact that folks don't respond doesn't mean that they don't care,
      or that they aren't interested. Sometimes is just means that they don't
      know enough to add to the conversation :)

      just one more mile (but not today)
      jim p.
      ...in scott$dale, where it is a gorgeous day. I have nothing at all
      physical planned today; yesterday was bench press day, tomorrow is 8 trail
      miles easy and dead lift day. And maybe hiking and/or climbing - Ethel
      hasn't told me. Is it bedtime yet?
      ------------------------------
      Date: Fri, 30 Dec 2005 09:28:33 -0800
      From: Karl Watanabe <karlw2000@...>
      Subject: Re: GPS v. Speed/Distance Unit?

      Neil wrote:

      For running purposes, or as Benji said "running log" purposes, I find the
      Polar 625x to be the best choice. Out of the box it is over 95% accurate,
      and if you calibrate it, it is even better. I also have the Forerunner 201
      and have stopped using it - in the city, even in Central Park, I lose signal
      too often to make it useful. In open spaces it is much better.

      ----

      I didn't know Polar used the similar speed pod as the NIke until I just looked it up. I wonder if Polar and Nike use the same technology because they are both spec'd to around 95% without calibration and 99% with. I have never used the Polar model, but I know I have always loved the features of the Nike watches...plus...they look a lot better. I'm sorry, but Polar watches look like crap. As soon as I got my first Nike Triax watch, I'd had nothing but good comments on the 'coolness' of the watch. Once a guy at a bridge toll booth said he thought the watch look cool.

      I couldn't tell from the Polar web sites I checked whether the HRM and speed are linked to the splits like the Nike is. I can get HR and speed for each split and the graphs show where the splits are marked.

      See:
      http://www.k3watanabe.com/Graphs/2x1600.gif
      http://www.k3watanabe.com/Graphs/2x800.gif
      http://www.k3watanabe.com/Graphs/4x400.gif

      I think someone like speedster EB would be more happy with the accuracy of the Polar or Nike vs the GPS units. He could then do his workouts without a track if he so desired. Last Wednesday on my 'easy' day, I tried the Nike in my company park where I had an 'estimated' 1/4 mile mapped out along with a 0.1 mile recovery jog. I did the loop 3 times and came up with 0.248 miles on my '1/4' and 0.096 on my 0.1 mile recovery. Not bad if I do say so myself as the distance was just based on my experience from my 'fast' days years ago. Now I can use the Nike with confidence.

      ORN: About to head out for some rowing and shopping ;).

      regards,
      Karl Watanabe
      Santa Clara, CA. USA
      ------------------------------




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