Big John wrote:
Believe it or not, this part is actually a very simple calculation. It's basically the Pythagorean theorem.
Are you assuming a flat earth?
Big John wrote:
Believe it or not, this part is actually a very simple calculation. It's basically the Pythagorean theorem.
Are you assuming a flat earth?
Most run long on the track too, as it's measured from most inside part of the lane. Such is life.
cold day today wrote:
Are you assuming a flat earth?
No, just measuring the distance between two points using d^2=x^2+y^2+z^2. Note when I say "simple calculation" I am assuming however that we have a computer or at least a calculator handy.
Fastnbulbous wrote:
Most run long on the track too, as it's measured from most inside part of the lane. Such is life.
Tracks ARE NOT measured "from most inside part of the lane."
Last I checked NFHS & USATF require measurement 8"(20 cm) from the nearer edge of the lane which is on the runner's left. If the inside lane line has a raised curb - the measuremnt shall be 12"(30cm) into the lane from the raised curb.
Funny story: A local training group was doing a two mile time trial on the track. All of the runners were crossing the finish line and the coach was cheering everyone on when he looked 80 meters down the track and saw one girl walking. He started yelling for her to make it all the way in when she proclaimed her garmin told her she had already done the two miles.
Well, I don't measure courses but I love the Garmin GPS that I use because it seems to be very beneficial for daily workouts/runs and keeping track of mileage/pace etc. I don't need to stay on a remeasured course or anything...Just go anywhere I want.
Although, I do have to say that my HS coach measures our 5k courses with his TRUCK, and my GPS says that it is over .1miles off. Pretty bad. I never trust my PRs on these courses.
cold day today wrote:
No, just measuring the distance between two points using d^2=x^2+y^2+z^2. Note when I say "simple calculation" I am assuming however that we have a computer or at least a calculator handy.
It's not that simple. The formula for calculating the distance between two points (latitude,longitude) on a sphere is given in the following link.
Sorry, that should have been...
Big John wrote:
No, just measuring the distance between two points using d^2=x^2+y^2+z^2. Note when I say "simple calculation" I am assuming however that we have a computer or at least a calculator handy.
RaceMeasure wrote:
I have set my units to record a point as often as possible, using the distance method. This allows a trackpoint every 1/100 of a mile, or 52 feet. The segments are anywhere from 40 to 65 feet in length, so even when set to measure every 52 feet, it varies. Sharp turns are rarely tracked properly. I have also set them (when I am not measuring a race course) to measure every 5 seconds, or 1 second, and the tracks are not smooth. Straight lines from one point to the next, but very jagged, and not in the straight line that was ridden.
The distance a GPS device will give you is always less accurate using this method. Sure Garmin's manual makes it sound like recording every second will give you the most accurate results, but I found the GPS would give me distances that were much too long and very jagged courses in this mode. When using "Smart Recording", the tracks might have been off the trail I was running, going through buildings, etc, but they were straight and the distances much more reliable.
Aghast wrote:
I would like a GPS watch that lets you first input the run you want to do by using a program like google earth and mapping out your run. Then you download that map into the watch and start the run. Now the watch has a reference point for your intended path from which to calculate a more accurate speed and distance.
You can probably hack this onto Garmin Forerunners. They have "Courses", which their software only lets you create from previous runs, but it's well documented (by Garmin) what the data you have to send to the watch describing a course looks like.
Th
dukerdog wrote:
It's not that simple. The formula for calculating the distance between two points (latitude,longitude) on a sphere is given in the following link.
http://en.wikipedia.org/wiki/Great-circle_distance
That's a good approximation if all you have is latitude and longitude, but you would still have to make at least some sort of guess at your altitude to use the great circle equation. If you can get all three coordinates from your receiver then the x^2+y^2+z^2 deal is the better way to go.
hahahahahahahahahahahaaaaaaaaaaaaaaa my goodness some people are dense.
LVD wrote:
I've read all of the links, but I still for the life of me do not understand why every race I've ever run is long. I thought it was just me, but I've discussed this with all of my friends, and they all say that all of their races are long, too.
Just amazing.
Big John wrote:
Th
dukerdog wrote:It's not that simple. The formula for calculating the distance between two points (latitude,longitude) on a sphere is given in the following link.
http://en.wikipedia.org/wiki/Great-circle_distanceThat's a good approximation if all you have is latitude and longitude, but you would still have to make at least some sort of guess at your altitude to use the great circle equation. If you can get all three coordinates from your receiver then the x^2+y^2+z^2 deal is the better way to go.
The poit I'm making is to try all these calculations and compare to your gps total distance to figure out what it's doing in order to evaluate its error. GMT is a set of free mapping tools that will probably simplify the work.
Big John wrote:
Th
dukerdog wrote:It's not that simple. The formula for calculating the distance between two points (latitude,longitude) on a sphere is given in the following link.
http://en.wikipedia.org/wiki/Great-circle_distanceThat's a good approximation if all you have is latitude and longitude, but you would still have to make at least some sort of guess at your altitude to use the great circle equation. If you can get all three coordinates from your receiver then the x^2+y^2+z^2 deal is the better way to go.
Both are actually "flat earth" models 1) the wiki equations are based on a flat sphere (that is no altitude) while 2) pythagorus is based on a planar surface with undulation. For GPS, it simply doesn't matter. The distance between two coordinates that are only 50 - 100 feet apart on a sphere the size of the earth is the same the same either way to many decimal places. What people don't seem to realize even though its been stated frequently on these boards is that hills don't matter to these calculations because the distance climbed is far less than the error in the gps. For mount washington, the flat vs. 3-d distance is 264 feet over 7.6 miles.
The question still remains: what kind of a douchebag sues over the length of a race course??? Someone with a VERY empty life .....
Big John wrote:
Believe it or not, this part is actually a very simple calculation. It's basically the Pythagorean theorem.
You mean the one where the squaw on the hippopotamus is the sum of the squaws on the other two hides?
(sorry, reaaaly old math joke)
Why do you think the world record on the track is always faster than on the road?
Everything is simple if you're not the person who has to do it.
When you download track points from a GPS it gives those to you in spherical coordinates, not cartesian coordinates (x,y,z). The earth's radius varies by about 0.5%. You can assume it is constant for all your track points, but you have to know what it is at your location. All of the formulas that are given for the geodesic distance are approximations. How much of an approximation? Within 1%, within 0.1%, I don't know. You'd have to research all of this and get it all right to have the level of precision you would need to determine if Garmin just connects the dots to determine distance.
For those who say there are plenty of online tools that will do this, or help you do this, yes, there are. One of them is Google Earth, and that's the one I used. When I used it to calculate the distance of one of my tracks, I got a different answer than my GPS gave me. It was close, but it was not the same. But this isn't something I've been really careful about checking yet. Google Earth just added the feature of calculating the distance of a "path" as they call them.
You can download GPS tracks in cartesian format...and many others as well. Somewhere on the menu or settings screen (depending on the make/model) you can select the coordinate type. Fact is that spherical coordinates are not *always* the best ones to work in. I personally think it's simpler to do the math in cartesian coordinates, but that's just me.
The math is easier in Cartesian coordinates, but it becomes more difficult to treat the altitude measurement differently than the horizontal measurement. The altitude error in the GPS system is inherently a few times greater than the horizontal error. If you include the altitude component you've essentially given the proverbial collie wings and the directional sense of a butterfly.