I haven't done it on a straight course, but I've done it a couple times on race courses that I've measured with my bike.
https://measure.infopop.cc/eve/...9510622/m/9611072113
All these comments and tests have made it clear that when a runner uses a GPS they will not give accurate results.
Bob Baumel has pointed out the following on a GPS:
A runner that uses a GPS can have errors on the order of several meters (sometimes as much as 20 m)—and that’s just in measuring the location of a single point. Errors dealing with course length are much greater, as the course must be approximated by making point measurements at some number of points along the course, and the overall error depends on how densely the points are sampled, the errors in locating the individual points (inevitably mis-positioned somewhat to left or right of the true path), and the algorithm used in calculating the course length from all the point locations. Also, some points along the course may not have clear views of the satellites used in making GPS measurements, resulting in very large errors in locating those points.
The RRTC/USATF as stated by one of the responders needs to have something posted on the fact that a GPS in most cases will produce long a measurements. We are currently working on coming up with just that.
Bob Baumel has pointed out the following on a GPS:
A runner that uses a GPS can have errors on the order of several meters (sometimes as much as 20 m)—and that’s just in measuring the location of a single point. Errors dealing with course length are much greater, as the course must be approximated by making point measurements at some number of points along the course, and the overall error depends on how densely the points are sampled, the errors in locating the individual points (inevitably mis-positioned somewhat to left or right of the true path), and the algorithm used in calculating the course length from all the point locations. Also, some points along the course may not have clear views of the satellites used in making GPS measurements, resulting in very large errors in locating those points.
The RRTC/USATF as stated by one of the responders needs to have something posted on the fact that a GPS in most cases will produce long a measurements. We are currently working on coming up with just that.
Pete, a GPS on my wrist travels in a pretty-much horizontal plane. However, my belly button travels up and down as I age - I mean run. 
This is my first post on this forum so best I introduce myself. A significant part of my career has been involved with Satcom ( 18 years with geosynchronous SV's) and more recently with GPS and product performance testing. Much of what has been posted is on point however the reasoning behind it borders conjecture. The GPS system send down GPS packet data at a predetermined 1hz rate (1 per second). We have no control over that. Some products record at half that rate only recording every other GPS point. Distance accuracy is only one measure of an accurate GPS workout. TTFF ( time to acquire a satellite fix) is very important. Positional accuracy at TTFF, Altitude accuracy at TTFF etc etc. Some products perform "smoothing" which will provide a better looking graph but affects accuracy. Some manufacturers include a "fudge factor" to compensate for a poorly tuned antenna/reciever pairing. It's great when the run comes up short but will over report when the distance actually comes in accurate. I do side by side by side testing with significant controls and very accurate reference equipment capable of decimeter accuracy. GPS should NEVER report long, NEVER. Tendency is to miss points along the way not generate distance. Sufficient algorithms are in the firmware of the big player GPS watches that handle arm movement artifacts to varying degrees. The latest technology is to get extended emphemeris from cell tower broadcasts or from server generated sites when you offload your workout. The emphemeris could be good(accurate) for up to 7 days in some instances. The GPS system has so many variables affecting any given workout, some of which were mentioned above, like tall buildings( multipath), wet canopy attenuation,time of day, atmospheric interference, etc etc.
I'll stop here since I could go on and on about anything relating to GPS and especially about accuracy. I would entertain any specific questions and anawer as time allows. I'm looking forward to some interesting reading.
Robert
I'll stop here since I could go on and on about anything relating to GPS and especially about accuracy. I would entertain any specific questions and anawer as time allows. I'm looking forward to some interesting reading.
Robert
Robert, I will let others respond. However, much testing over accurately measured courses have proven to show a GPS used by runners produce long measurements.
As an example, just using a simple measured 1000' foot course came up with about a .5% error(the GPS measured long).
When runners use a GPS on a certified course, in most cases they don't run the shortest possible route. Hence, the GPS will show a long course.
As an example, just using a simple measured 1000' foot course came up with about a .5% error(the GPS measured long).
When runners use a GPS on a certified course, in most cases they don't run the shortest possible route. Hence, the GPS will show a long course.
Robert,
If you use a GPS where there are no obstructions(trees, buildings, ect) and have a clear view of the sky the GPS will be accurate. My view is a GPS does measure long in most road races because they don't have a clear view of the sky.
If you use a GPS where there are no obstructions(trees, buildings, ect) and have a clear view of the sky the GPS will be accurate. My view is a GPS does measure long in most road races because they don't have a clear view of the sky.
My GPS devices will sometimes report distances that are slightly long and sometimes report distances that are slightly short. The distance they report is a function of the algorithm the manufacturer has written to calculate the distance from the raw GPS data. It is certainly possible that the algorithm will calculate a distance that is sometimes an overestimate.
So I don't know what you mean when you say a "GPS should never report long."
So I don't know what you mean when you say a "GPS should never report long."
Let me say, I should have prefaced maybe with, "in a perfect world". I know most wrist worn GPS devices will report long but as a result of "post-processed" data. Where there is multi-path, like urban canyon environment( city marathons) it's a crapshoot. Distance can be way long or intolerably short depending on severity. Even the marketplace's hands down favorites have produced bad runs when worn on the same wrist in the same workout against "inferior" product. When our team measures for distance accuracy, the course has to be traversed exactly as measured by wheel or GPS, otherwise the GPS is doing its job and reporting distance as it was traveled. Lots of variables to consider and manufacturers solve their issues differently depending on the expectations of the user. I'll try to be more "User-centric" than engineering in future posts. Love the comments and the information from runners and cyclist!!
Here’s an article from the ArcUser magazine titled Recreational Versus Professional GPS: What's the Difference? The article is available online from http://www.esri.com/news/arcuser/0104/rec-gps.html. I pasted the text below.
Enjoy. -- Justin
Recreational Versus Professional GPS: What's the Difference?
Good decisions require good information. For GIS users, the quality of information coming out of their systems depends on the accuracy of the data going in. Confident decision making leaves no room for doubt over data accuracy. The last thing GIS users need to worry about is whether the data collected by GPS meets the accuracy requirements of the intended application.
When shopping for a GPS receiver, GIS users should evaluate GIS application against functionality and features of GPS receivers in their price range.
Given the large number of products on the market, selecting the right GPS receiver can be difficult. With budgets tightened everywhere, some GIS users have begun looking at and buying less expensive recreational GPS products that are popular with outdoor enthusiasts. New features, such as ruggedized cases and differential correction, and a price tag often below $500 make these units attractive compared with higher-priced professional-grade GPS receivers.
But beware, as is true with most products, you get what you pay for. There is a significant difference in the accuracy of location data acquired by recreational GPS receivers versus the professional units. The 10-meter error typical of a recreational model won't cause a major problem for a hiker in the woods, but such inaccuracy may not be acceptable for GIS applications.
Accuracy, Accuracy, Accuracy
Recreational and professional GPS units are designed and built for different purposes. A recreational GPS unit is designed to acquire a location fix quickly without the need for pinpoint accuracy because hikers can find their campsite once they get within 10 meters of it. GIS users, on the other hand, typically require extremely accurate placement of features often to within a meter or less so that data layers can be overlaid and intricate spatial relationships can be determined.
Although recreational products are not specifically designed for GIS mapping, they can be used successfully in some applications. And for some GIS users, the recreational products may be the most cost-effective choice. In choosing between a recreational and a professional GPS receiver, GIS users should answer the following questions to be certain the selected unit will meet their application needs.
* Do you need to integrate data seamlessly with a GIS?
If you will be converting GPS points to a specific GIS format, such as shapefile format, you should purchase a professional-grade GPS receiver. Some newer units can even convert points to popular GIS formats on the fly during downloading. Most recreational receivers cannot convert data to other formats.
* Will you be collecting attributes along with location points?
Many GIS users have found that accurate attribute collection is just as crucial as location acquisition. Only the professional GPS products offer customizable interfaces and routines for detailed attribute collection.
* Is five-meter accuracy sufficient for your application?
A recreational GPS is typically able to achieve 10-meter accuracy in autonomous mode, but some now can handle real-time differential correction capable of sharpening accuracy to five meters or better. In this situation, the most cost-effective purchase may be the recreational unit.
* Is submeter accuracy required for your application?
For many GIS users, accuracy is measured in centimeters. In these cases, professional GPS units are the only ones capable of performing the differential postprocessing required to achieve this level of accuracy.
Other Considerations
After price, data quality and accuracy are the main differentiators between recreational and professional units that influence the buying decision of a GIS user. Engineering, design, and construction characteristics account for the variation in capabilities among GPS receivers. Professional units have been engineered and built to acquire more accurate location coordinates. Although many design features contribute to this higher level of performance, three factors—quality control, electromagnetic shielding, and antenna technology—set GIS-grade products apart from recreational receivers.
Quality Control— Professional GPS units give users control over the quality of the position points that are collected. Through a simple interface, the user can establish specific thresholds for acceptable data quality. For instance, the user chooses the number of satellites and position above the horizon needed to achieve suitable accuracy. The user can also program the receiver to disregard any satellite signals that suffer from too much noise interference. These quality control settings essentially allow the user to filter out any potentially poor data that may degrade the overall quality of the location coordinates, resulting in greater accuracy in the final dataset.
Electromagnetic Shielding—Signals from GPS satellites are very weak and can easily be degraded by interference from nearby electronic devices such as laptop computers or personal digital assistants (PDAs). Given the fact that many GPS receivers and GPS cards are linked to computers and PDAs, this can pose a serious problem. High-end GPS products have built-in shielding technology that minimizes the effects of stray electromagnetic signals from other equipment.
Antenna Technology— Weak GPS signals require a sensitive antenna, especially when receiving transmissions in urban canyons and under tree canopies. The antennas provided with professional grade GPS units are designed to pick up signals in almost any environment. More important, high-end antennas protect against interference from multipath signals. These signals from GPS satellites have been degraded by bouncing off buildings and other overhead features on their way to the receiver on the ground. Multipath signals can significantly reduce the accuracy of location calculations. However, antennas on professional receivers recognize and filter out multipath signals.
Confidence: The Final Differentiator
For GIS users, settling for a receiver that collects data less accurate than is required by the GIS application will cast doubts over management decisions based on the information coming out of the system. While shopping for a GPS receiver, GIS users should honestly compare the needs of their GIS application with the GPS receivers in their price range.
# # #
Enjoy. -- Justin
Recreational Versus Professional GPS: What's the Difference?
Good decisions require good information. For GIS users, the quality of information coming out of their systems depends on the accuracy of the data going in. Confident decision making leaves no room for doubt over data accuracy. The last thing GIS users need to worry about is whether the data collected by GPS meets the accuracy requirements of the intended application.
When shopping for a GPS receiver, GIS users should evaluate GIS application against functionality and features of GPS receivers in their price range.
Given the large number of products on the market, selecting the right GPS receiver can be difficult. With budgets tightened everywhere, some GIS users have begun looking at and buying less expensive recreational GPS products that are popular with outdoor enthusiasts. New features, such as ruggedized cases and differential correction, and a price tag often below $500 make these units attractive compared with higher-priced professional-grade GPS receivers.
But beware, as is true with most products, you get what you pay for. There is a significant difference in the accuracy of location data acquired by recreational GPS receivers versus the professional units. The 10-meter error typical of a recreational model won't cause a major problem for a hiker in the woods, but such inaccuracy may not be acceptable for GIS applications.
Accuracy, Accuracy, Accuracy
Recreational and professional GPS units are designed and built for different purposes. A recreational GPS unit is designed to acquire a location fix quickly without the need for pinpoint accuracy because hikers can find their campsite once they get within 10 meters of it. GIS users, on the other hand, typically require extremely accurate placement of features often to within a meter or less so that data layers can be overlaid and intricate spatial relationships can be determined.
Although recreational products are not specifically designed for GIS mapping, they can be used successfully in some applications. And for some GIS users, the recreational products may be the most cost-effective choice. In choosing between a recreational and a professional GPS receiver, GIS users should answer the following questions to be certain the selected unit will meet their application needs.
* Do you need to integrate data seamlessly with a GIS?
If you will be converting GPS points to a specific GIS format, such as shapefile format, you should purchase a professional-grade GPS receiver. Some newer units can even convert points to popular GIS formats on the fly during downloading. Most recreational receivers cannot convert data to other formats.
* Will you be collecting attributes along with location points?
Many GIS users have found that accurate attribute collection is just as crucial as location acquisition. Only the professional GPS products offer customizable interfaces and routines for detailed attribute collection.
* Is five-meter accuracy sufficient for your application?
A recreational GPS is typically able to achieve 10-meter accuracy in autonomous mode, but some now can handle real-time differential correction capable of sharpening accuracy to five meters or better. In this situation, the most cost-effective purchase may be the recreational unit.
* Is submeter accuracy required for your application?
For many GIS users, accuracy is measured in centimeters. In these cases, professional GPS units are the only ones capable of performing the differential postprocessing required to achieve this level of accuracy.
Other Considerations
After price, data quality and accuracy are the main differentiators between recreational and professional units that influence the buying decision of a GIS user. Engineering, design, and construction characteristics account for the variation in capabilities among GPS receivers. Professional units have been engineered and built to acquire more accurate location coordinates. Although many design features contribute to this higher level of performance, three factors—quality control, electromagnetic shielding, and antenna technology—set GIS-grade products apart from recreational receivers.
Quality Control— Professional GPS units give users control over the quality of the position points that are collected. Through a simple interface, the user can establish specific thresholds for acceptable data quality. For instance, the user chooses the number of satellites and position above the horizon needed to achieve suitable accuracy. The user can also program the receiver to disregard any satellite signals that suffer from too much noise interference. These quality control settings essentially allow the user to filter out any potentially poor data that may degrade the overall quality of the location coordinates, resulting in greater accuracy in the final dataset.
Electromagnetic Shielding—Signals from GPS satellites are very weak and can easily be degraded by interference from nearby electronic devices such as laptop computers or personal digital assistants (PDAs). Given the fact that many GPS receivers and GPS cards are linked to computers and PDAs, this can pose a serious problem. High-end GPS products have built-in shielding technology that minimizes the effects of stray electromagnetic signals from other equipment.
Antenna Technology— Weak GPS signals require a sensitive antenna, especially when receiving transmissions in urban canyons and under tree canopies. The antennas provided with professional grade GPS units are designed to pick up signals in almost any environment. More important, high-end antennas protect against interference from multipath signals. These signals from GPS satellites have been degraded by bouncing off buildings and other overhead features on their way to the receiver on the ground. Multipath signals can significantly reduce the accuracy of location calculations. However, antennas on professional receivers recognize and filter out multipath signals.
Confidence: The Final Differentiator
For GIS users, settling for a receiver that collects data less accurate than is required by the GIS application will cast doubts over management decisions based on the information coming out of the system. While shopping for a GPS receiver, GIS users should honestly compare the needs of their GIS application with the GPS receivers in their price range.
# # #
This article, titled GPS Watch Can Be an Unreliable Running Partner and written by Gina Kolata, appeared in the NY Times in December 2011. The complete article is available online at http://www.nytimes.com/2011/12/20/health/nutrition/gps-watches-may-not-track-runs-accurately.html. I pasted the text below.
GPS Watch Can Be an Unreliable Running Partner
By GINA KOLATA
Published: December 19, 2011
I used to run with a GPS watch, and at the time it seemed like a technological marvel.
Made by Polar, Garmin, Nike and Timex, global positioning system watches track the distance you have run and your pace, including your average pace and your instantaneous pace. They beep at intervals, like every mile, if you want to train by doing some segments of your course at a faster pace. And when you are finished running, you can download all your data onto your computer.
But after a while, I noticed something disconcerting. My watch might record my run as, say, six miles, but according to Google Maps, the actual distance was more like 6.5 miles.
That kind of discrepancy, of course, plays havoc with your training. The pace calculated by the watch is much too slow, and the run becomes an exercise in frustration.
So I got another watch, from a different maker. It was just as bad, maybe worse. I returned it and got a third one, but that one seemed to be absolutely accurate only once, when I was running along the lakefront in Chicago, under a clear sky with no tall buildings and few trees nearby.
On Sunday, I tried a little experiment with friends who also have GPS watches. I started from my house, and Jen Davis and Martin Strauss started from her house; we met up along the way.
My route was 15.96 miles, according to Google Maps. My watch said it was 15.54. Jen’s watch, an older model, did much better. Her route was 19.1 miles. Her watch said 19.02.
Race organizers know this problem all too well. Douglas Thurston, operations director for the Competitor Group, which organizes Rock ’n’ Roll Marathons, a series of races across the country, braces himself for complaints with every race.
Runners who wore GPS watches start e-mailing him or posting comments on Facebook or Twitter afterward. The course was measured incorrectly, they will say. According to their GPS devices, it was too short.
Mr. Thurston has gotten so used to the complaints that he actually has a generic e-mail reply. No, it says, the course was not wrong. Your GPS device was.
“If someone wants to go to mat on it, I ask them to go to a 400-meter track and run on the inside lane for 12.5 laps. That’s 5,000 meters,” he said in an interview. Then, he tells the runner, check the distance on your GPS device. He guarantees it will not be 5,000 meters.
Martin illustrated this for me recently by running five times around a track at the University of Michigan, where he is a professor of mathematics and electrical engineering and computer science. When he downloaded the GPS data onto his computer, every loop around the track was a little different, and none were oval.
Martin Strauss, via Garmin and Microsoft
In fact, not one of his paths was even curved — they were short segments of lines connected to resemble an oval. Yet he had run in the same lane.
It seems clear enough that a GPS watch is not very accurate, yet online runners’ forums, like one at the Web site of Runners World, are filled with comments from confused athletes who rely on the devices. One poster, for example, ran a half marathon and wore a GPS watch that said the distance was 12.8 miles instead of 13.1.
“Many people are posting on the race’s Web site that theirs came up just as short,” the runner wrote. “I got a pretty stellar PR” — personal record — “and would hate to have a question mark hanging over it.”
Another wrote, “I did an out-and-back run on a rail trail: 5.25 miles out and 5.02 miles back. According to the GPS, I was running 40 m.p.h. for over two minutes.”
What’s wrong with those GPS devices? The problem, say their makers, is that people expect too much. The watches are very much a work in progress. “We all use pretty much the same technology,” said Corey Cornaccio, director of marketing at Polar. The technology is improving, but some inaccuracy remains. “People don’t understand that,” he said.
Trees or clouds or tall buildings can block the satellite signals needed for the devices to track distances. Routes with lots of turns throw them off, too; if you lose the signal as you go around a curve, your device will draw a straight line from where it last saw you to where it found you again. The distance around the curve will not be tracked.
Also, says Martin, there is an accuracy problem caused by something called multipath. “If a satellite signal arrives directly and also bounces off a mountain or nearby building to the receiver, the receiver may be confused as to which signal to use,” he said.
Then again, we had perfect conditions on Sunday — a sunny day, a route with few turns on country roads lined mostly with fields. And my GPS watch still was wrong.
And even though the technologies — and sources of error — are pretty much the same across different devices, they can give sometimes wildly different results, as one runner, 21-year-old Allen Helton, of Richardson, Tex., discovered. Mr. Helton, a college student who works at a running store, recently decided to test GPS watches sold by different makers, older and newer models, on a variety of courses.
All got distances wrong, and none agreed with the others on any of Mr. Helton’s tests. But their worst performance was, as Mr. Helton expected, on a trail run, with trees and twists and turns.
The actual distance was 6.6 miles, and his actual pace was 7 minutes, 37 seconds a mile. The watch that did best said he ran 6.45 miles at a 7:47 pace. The one that did worst said he ran just 5.5 miles at a 9:08 pace.
But Mr. Helton is not throwing his watches away. He has three GPS watches and uses one nearly every time he runs. Then again, unlike most areas where I run, his routes do not have large trees, winding roads and poor satellite reception. On his routes, Mr. Helton said, his GPS device is accurate to within 10 feet of where he actually is.
“To me, that is a very, very accurate watch,” he said.
# # #
GPS Watch Can Be an Unreliable Running Partner
By GINA KOLATA
Published: December 19, 2011
I used to run with a GPS watch, and at the time it seemed like a technological marvel.
Made by Polar, Garmin, Nike and Timex, global positioning system watches track the distance you have run and your pace, including your average pace and your instantaneous pace. They beep at intervals, like every mile, if you want to train by doing some segments of your course at a faster pace. And when you are finished running, you can download all your data onto your computer.
But after a while, I noticed something disconcerting. My watch might record my run as, say, six miles, but according to Google Maps, the actual distance was more like 6.5 miles.
That kind of discrepancy, of course, plays havoc with your training. The pace calculated by the watch is much too slow, and the run becomes an exercise in frustration.
So I got another watch, from a different maker. It was just as bad, maybe worse. I returned it and got a third one, but that one seemed to be absolutely accurate only once, when I was running along the lakefront in Chicago, under a clear sky with no tall buildings and few trees nearby.
On Sunday, I tried a little experiment with friends who also have GPS watches. I started from my house, and Jen Davis and Martin Strauss started from her house; we met up along the way.
My route was 15.96 miles, according to Google Maps. My watch said it was 15.54. Jen’s watch, an older model, did much better. Her route was 19.1 miles. Her watch said 19.02.
Race organizers know this problem all too well. Douglas Thurston, operations director for the Competitor Group, which organizes Rock ’n’ Roll Marathons, a series of races across the country, braces himself for complaints with every race.
Runners who wore GPS watches start e-mailing him or posting comments on Facebook or Twitter afterward. The course was measured incorrectly, they will say. According to their GPS devices, it was too short.
Mr. Thurston has gotten so used to the complaints that he actually has a generic e-mail reply. No, it says, the course was not wrong. Your GPS device was.
“If someone wants to go to mat on it, I ask them to go to a 400-meter track and run on the inside lane for 12.5 laps. That’s 5,000 meters,” he said in an interview. Then, he tells the runner, check the distance on your GPS device. He guarantees it will not be 5,000 meters.
Martin illustrated this for me recently by running five times around a track at the University of Michigan, where he is a professor of mathematics and electrical engineering and computer science. When he downloaded the GPS data onto his computer, every loop around the track was a little different, and none were oval.
Martin Strauss, via Garmin and Microsoft
In fact, not one of his paths was even curved — they were short segments of lines connected to resemble an oval. Yet he had run in the same lane.
It seems clear enough that a GPS watch is not very accurate, yet online runners’ forums, like one at the Web site of Runners World, are filled with comments from confused athletes who rely on the devices. One poster, for example, ran a half marathon and wore a GPS watch that said the distance was 12.8 miles instead of 13.1.
“Many people are posting on the race’s Web site that theirs came up just as short,” the runner wrote. “I got a pretty stellar PR” — personal record — “and would hate to have a question mark hanging over it.”
Another wrote, “I did an out-and-back run on a rail trail: 5.25 miles out and 5.02 miles back. According to the GPS, I was running 40 m.p.h. for over two minutes.”
What’s wrong with those GPS devices? The problem, say their makers, is that people expect too much. The watches are very much a work in progress. “We all use pretty much the same technology,” said Corey Cornaccio, director of marketing at Polar. The technology is improving, but some inaccuracy remains. “People don’t understand that,” he said.
Trees or clouds or tall buildings can block the satellite signals needed for the devices to track distances. Routes with lots of turns throw them off, too; if you lose the signal as you go around a curve, your device will draw a straight line from where it last saw you to where it found you again. The distance around the curve will not be tracked.
Also, says Martin, there is an accuracy problem caused by something called multipath. “If a satellite signal arrives directly and also bounces off a mountain or nearby building to the receiver, the receiver may be confused as to which signal to use,” he said.
Then again, we had perfect conditions on Sunday — a sunny day, a route with few turns on country roads lined mostly with fields. And my GPS watch still was wrong.
And even though the technologies — and sources of error — are pretty much the same across different devices, they can give sometimes wildly different results, as one runner, 21-year-old Allen Helton, of Richardson, Tex., discovered. Mr. Helton, a college student who works at a running store, recently decided to test GPS watches sold by different makers, older and newer models, on a variety of courses.
All got distances wrong, and none agreed with the others on any of Mr. Helton’s tests. But their worst performance was, as Mr. Helton expected, on a trail run, with trees and twists and turns.
The actual distance was 6.6 miles, and his actual pace was 7 minutes, 37 seconds a mile. The watch that did best said he ran 6.45 miles at a 7:47 pace. The one that did worst said he ran just 5.5 miles at a 9:08 pace.
But Mr. Helton is not throwing his watches away. He has three GPS watches and uses one nearly every time he runs. Then again, unlike most areas where I run, his routes do not have large trees, winding roads and poor satellite reception. On his routes, Mr. Helton said, his GPS device is accurate to within 10 feet of where he actually is.
“To me, that is a very, very accurate watch,” he said.
# # #