12345

Trying to ONLY run 26.2 miles in a marathon (Read 2200 times)


an amazing likeness

    I synched it up, and it tells me how well it is synched which the running versions do not -- accuracy +/- 75 feet.
    Not sure why you think the running Garmin ForeRunner x05 units don't give current satellite information -- they all have displays for current accuracy as well as the satellite constellation in use. Mine is nearly always reports 15 - 22 feet as accuracy during my runs.

    Choosing my words carefully has never been my strength I've been known to be vague and often pointless

      Think of it this way: Let's start with accuracy, you can agree with the best case of +/- 14 feet or even Spaniels +/- 76feet (that'll even make the argument more convincing). Picture yourself running along, draw a circle around yourself with radius of 14 feet (oops, first mistake - it's actually a sphere, up and down must be included). So you're running along and for every point the GPS measures it can have you 14 feet ahead, behind, to the right, to the left, below ground or up in the air. Every single point. The points it measures directly inline with the direction you are traveling will, arguably, cancel out - but not the others. This is why you'll never see a Garmin measure a certified, accurate distance SHORT, it will always be long. Not because of tangents but because of this inherent inaccuracy. Tangents will make it even longer but, unless you were totally crazy about running tangents the longest way possible, I don't see how this could be even close to GPS inaccuracy. No data but that's the reasoning I've come up with as to why I believe GPS inaccuracy is the main culprit in Garmin Forerunner course distance over-measurements. MTA: Caveat - If you have the Garmin set to 'record-every-point' the above discussion stands. If you have the Garmin set to 'Smart Data Recording' a slight mod is needed. In this case, the accuracy will probably be BETTER than 'record-every-point' if there are long sections of straight trail/roadway'. This is because in Smart Recording mode the software will 'decide' whether you are running a straight line and then go back and delete intermediate points (and their inaccuracies) and then interpolate between the two endpoints of that segment. If someone had a accurately, conventionally measured (Jones counter?) 5mile distance (has to be long to get any significant data) on a very straight and flat road or trail you could verify this. I don't think the Garmin would ever measure it short unless it was in Smart Recording mode. In the other mode it would ALWAYS record the distance long and, obviously, would have nothing to do with running any tangents the long way.


      an amazing likeness

        However, .02 for 5 miles = 7.2 seconds at 6-minute per mile pace. At 8-min pace it becomes almost 10 seconds. This is quite significant, imo, and is multiplied as the distance increases.
        I'm sorry Jim, but I can't follow this line of argument at all. In a race, the only time that counts is the official one and the pace will determined using the office course distance -- what my Garmin measures for distance and records for time & pace are irrelevant. I didn't gain or loose 10 seconds for that .02 miles beyond 5m in that race -- All it tells me is that I ran longer than the minimum possible course distance. By just a little. Over a course which uses a winding path along a river for a section. The course was accurate (I assume, because certified courses are some very high % of time), and the time was accurate (I assume, because chip timed well-run races are some very high % of time), and both those independently confirm the accuracy of the data my Garmin recorded. Armed with the set of facts I have, colored by all my own preconceptions and biases, I struggle to accept the argument that the original poster's experience of recording 26.6 miles for two marathons is all caused by her Garmin's GPS recording characteristics. I believe that the road (non track) runner's inability to run the exact measurement line of the course has a major impact and the GPS impact is minor.

        Choosing my words carefully has never been my strength I've been known to be vague and often pointless


        I've got a fever...

          From Malmo's discussion of VO2max, but I think it still applies...
          The only numbers that matter are the ones that you receive at the end of the race. The most important of these is called place, and is represented as an ordinal. A '1' is the best indicator of your performance. If you get a '1' then you've done excellent. It's no small coincidence that '1' is a homophone for 'won'. Other excellent numbers to receive are '2' and '3'. Not nearly as good as a '1', but by tradition and convention the numbers '1', '2' and '3' are deemed to be the 'supreme ordinals'; that is to say, worthy of gold, silver and bronze, and are segregated from the other ordinals. The rest of the ordinals are represented by the formula: n + 1...(to infinity). There is a direct, inverse relationship between ordinal value and its worth. The closer to the supreme ordinals, the better you've done, the closer to infinity, the worse you've done. One of the other numbers that matters much...is time. Time is always secondary to place in it's value. Neither place nor time are given in the gerbil-wheel lab tests conducted by the exercise-physio-geeks. You will only receive them in the experiment that the real experts call competition. Time does not supersede place, but it is a way of comparing the place of two or more experiments from different venues and eras...

          On your deathbed, you won't wish that you'd spent more time at the office.  But you will wish that you'd spent more time running.  Because if you had, you wouldn't be on your deathbed.


          Feeling the growl again

            Not sure why you think the running Garmin ForeRunner x05 units don't give current satellite information -- they all have displays for current accuracy as well as the satellite constellation in use. Mine is nearly always reports 15 - 22 feet as accuracy during my runs.
            I never said x05 units. What I did do was over-extrapolate my 201 experience to the other units which I do not own. Even with my handheld unit, which does give the information, it is clear that the resulting GPS measurements will never compare to a course certifier with a Jones counter carefully following the tangents of the course. The accuracy of my 201 has actually been quite comparable to acquaintances wearing newer units over runs. Even if you have +/- 14 feet, imagine running a marathon and every 25 yards you run left off the line of the course 14 feet, then 25 yards later 28 feet to end up 14 feet right of the line. What do you think that will do to your final distance run? This is a rough pictoral description of what is going on inside the GPS. As I stated earlier and was well put in another post, mis-plots directly in front and behind you are likely to cancel out. The left/right components of these mis-plots do NOT cancel, they are additive and will always end up giving you a long reading.

            "If you want to be a bad a$s, then do what a bad a$s does.  There's your pep talk for today.  Go Run." -- Slo_Hand

             

              I agree almost 100% (except for the x01 being as accurate as the x0-5), Spaniel! See my post above.


              Feeling the growl again

                So if you still do not think the best-case scenario of +/- 14 feet error can't cause the significantly long measurements during a marathon, read on: Let's make the following assumtions: 1) You have a satellite lock giving you the best-case scenario of +/- 14 foot accuracy on each measurement. 2) The GPS records one 14-foot deviation left or right of your actual location every 100 feet. Now, we can argue that every data point will not have a full 14-foot deviation left or right of the true path, and I agree. However you are also taking much more than one measurement every 100 feet, so I am balancing my assumption of one 14-foot error every 100 feet with the fact that in reality you will have a greater number of perhaps smaller (or potentially larger) errors within that 100 feet. So think of a right triangle. Side A is 100 feet (line from previous measurement to true location). Side B is 14 feet (ninety degrees to the right of true location). Side C is the hypoteneuse of the triangle, which is the line the GPS THINKS you took. Simple Pythagorean theorum 100^2 + 14^2 = C^2, so C=100.97 feet or 0.97 feet longer than you actually ran. A marathon is about 26.2 miles X 5280 feet = 138,336 feet, or about 1,383 100-foot segments. So 0.97 X 1,383 = 1,342 feet, or just over a quarter of a mile. Coincidentally or not, this is right in line with the 99% accuracy advertised for the 201. IMHO the newer units are not necessarily more accurate in good conditions, they just don't lose signal as easily and as a result are more accurate when the signal is poorer. MTA - Ken - See my last paragraph above. I would agree with you that the newer units have better antennas and hold signal better. The only time I've had accuracy problems with my 201 is when the signal is poorer, as this increases the likelihood of large, errant measurements (typically this is not manifested as a gradual increase in errors, but one or two large errors during a run). When conditions are good, my limited sample of runs with people with newer units show they are very close.

                "If you want to be a bad a$s, then do what a bad a$s does.  There's your pep talk for today.  Go Run." -- Slo_Hand

                 


                an amazing likeness

                  ...it is clear that the resulting GPS measurements will never compare to a course certifier with a Jones counter carefully following the tangents of the course...
                  With this specific point, I agree. Completely. If I've said something that opposes this statement, I have made a mistake, that wasn't my intent. You've all seen my perspective on this subject, so at this point, I am going to head off and look for an Ipod argument to join...

                  Choosing my words carefully has never been my strength I've been known to be vague and often pointless

                  DoppleBock


                    Until you get hit by a car! Clowning around
                    Of course - I do not wear an IPOD as that would be dangerous Big grin I run on a lot of running paths and even here I look for tangents. What really irritates me if when you can not tell on the marathon course which way a turn is until you get to it. I do not own a Gramin either. So of course I only run the exact distance I need to Smile

                    http://a-big-horse.blogspot.com/ 

                    2013 Goals ~ Mar < 3:00, 5M < 29, 10k < 35  

                     

                      I have learned from this thread that only thing better than geeking out over running stats from the Garmin is geeking out over the accuracy of the running stats from the Garmin.


                      an amazing likeness

                        If you have the Garmin set to 'record-every-point' the above discussion stands. If you have the Garmin set to 'Smart Data Recording' a slight mod is needed. In this case, the accuracy will probably be BETTER than 'record-every-point' if there are long sections of straight trail/roadway'. This is because in Smart Recording mode the software will 'decide' whether you are running a straight line and then go back and delete intermediate points (and their inaccuracies) and then interpolate between the two endpoints of that segment. If someone had a accurately, conventionally measured (Jones counter?) 5mile distance (has to be long to get any significant data) on a very straight and flat road or trail you could verify this. I don't think the Garmin would ever measure it short unless it was in Smart Recording mode. In the other mode it would ALWAYS record the distance long and, obviously, would have nothing to do with running any tangents the long way.
                        Ken, I understand the sphere of probably location pretty well, still appreciate your explanation. I have to challenge your description of every track point being off from the actual location by the sphere of probable location distance -- that's not correct. That is the maximum it will be off from the actual point when the sample is taken. My last marathon recorded 2,673 track points with an accuracy score of 22 feet. If I read your replies properly, you are implying that the Garmin reported distance (actually the distance comes from motionbased.com adding up all the track points in my case) would be 2,673 * 22 feet or 58,806 feet off from the actual distance covered. I don't really think that's the argument you are trying to make -- some of the track points are right on the money, some are up to 22' off -- there is a bell curve in the accuracy of the relationship between recorded location distance from actual location

                        Choosing my words carefully has never been my strength I've been known to be vague and often pointless


                        Feeling the growl again

                          I don't think Ken was implying that every point would be exactly any amount off, just that it could be. It's also an assumption that a bellcurve of points will be generated. We have no data to tell us what the shape of the curve will be.

                          "If you want to be a bad a$s, then do what a bad a$s does.  There's your pep talk for today.  Go Run." -- Slo_Hand

                           


                          On On

                            Also in your equation you assume all 2,673 points are off the same 22' in the same direction. That would be inaccurate. Some are off 22' in front, some to the back, some to the left, some to the right and also I guess some to the sky and some into the ground. Add them all together (some will cancel others out) for your discrepancy.
                            C-R


                              I have learned from this thread that only thing better than geeking out over running stats from the Garmin is geeking out over the accuracy of the running stats from the Garmin.
                              I'm somewhat of a tech geek and this thread frightens me.


                              "He conquers who endures" - Persius
                              "Every workout should have a purpose. Every purpose should link back to achieving a training objective." - Spaniel

                              http://ncstake.blogspot.com/


                              Bugs

                                In defense of the course and garmin accuraccy there was a port-o-potty a good 20 feet off course that was a necessary pitstop. You know if my garmin was off .5 mile in my long runs, I only ran one long run in training instead of six. Must have been my doom. Big grin

                                Bugs

                                12345