MyTracks - definities

Definitions

Track

A track is the breadcrumb trail that the GPS device logs. Every period (adjustable) the GPS device stores the current position, time and height (not all devices provide height, other devices provide an additional heartbeat again). A track is a list of all these points.

Route

If you start a trip, you can use a predefined route. Your GPS is doing its best to give you the right directions. A route whose format is not much different than one track, but obviously lacks some specific characteristics. These are the time and the height, because usually in the route maps are not available.

GPX file

This is the output file from the garmin (garmin XML). The format is described by Garmin, but the underlying basis is XML making it a good exchange format.
A file can GPX tracks, routes and waypoints. These are all shown on Mytracks.me. Mytrack.me expects at least one track in the file exists, otherwise an error message follow.

Colindex

This is an index which indicates the heaviness of a climb (col in french), according to the Dutch magazine 'Cycle'. This index can also naturally be applied to the whole trip. The same formula is then applied, which some assumptions.
Colindex = 0.0001 * altitude difference ^ 2 / (length / 2) (altitude difference [m], trip length in [km])

A GPS device

A GPS system is usually a small device that is capable of measuring satellite-based position on earth. The device stores the location in a track on a regular basis. Beside geographic location usually the height and time are saved.

American Measures

This site uses some American measures :
1 mile = 1609.344 m
1 foot� = 0.3048 m
1 pound = 0.45359237 kg

Energy

Cycling costs energy. From a day trip, with reasonable speed, you can easily burn hundreds kilocalories (kCal). The total energy consumed is the sum of power times the time (the integral for the mathematicians among us). For example for 100 seconds 100 watt power kicking, you have a work performed or energy supplied by a 100 * 100 = 10,000 Joules (J). The Joule is a measure of the amount of energy. Other known units of energy are the kilocalorie (kCal), and the kilowatt hour (kWh). These are easy to convert each other. (1 kCal = 4.2 kJ, and 1 kWh = 3600 kJ). The website http://www.xs4all.nl/~janfreak/drag.html gives an example of how speed and climb meters can be converted into power and energy. The GPX file provides all the information for that calculation to perform. So do we. This amount of energy that can be calculated from the GPX file, may significantly differ from the indication that a heart rate monitor indicates. That calculates the total number kCal consumed by the body. In contrast, only a small portion is converted into kinetic energy. On the internet I find factors (efficiency) of 25%. I think the performance of the human body is worse. Who can help me with a better indication of the efficiency of the human body?

Power

While cycling you have to overcome serveral kinds of forces. Roughly there are three forces at work on you when you go forward: the resistance of the bands on the road, including the resistance of chain and bearings, air resistance and the slope.
The GPS unit determines speed and altitude. It is easy to calculate the generated power. The sum (actually the integral) of all power bits per time unit, provides the total delivered energy or work.
The calculation on MyTracks is done with the formula:
Power = (Cr * m * g + ρ * Cw * A * v ^ 2 + m * g * slope) *v With Cr = a cycle-dependent parameter, set in 0003 at MyTracks
m = bike + rider + luggage weight in kg
g = gravitational acceleration (= 9.81 kgm / s ^ 2)
ρ = density of air (= 1.2 kg / m ^ 3)
Cw * A = resp. the drag coefficient and projected area (on MyTracks: Cw * A = 0.39)
slope = slope percentage/100
v = velocity
To successfully carry out this calculation some assumptions made, and you will be asked to pprovide a few extra parameters. in this case of the cyclist, including bike and luggage. The wind direction and strength are required. This ingredients are present to calculate the power with a reasonable accuracy.

The official unit for power is the watt (W).

Wind speed

Wind speed can be expressed in different ways. This site is the Beaufort (bft) used. The following table can help you to convert wind speed.

Strength (bft)	description	Speed in km/h	Speed in m/s	Speed in kts
0	Still	0-1	0-0.2	0-1
1	Weak	1-5	0.3-1.5	1-3
2	Weak	6-11	1.6-3.3	4-6
3	Moderate	12-19	3.4-5.4	7-10
4	Moderate	20-28	5.5-7.9	11-15
5	Rather strong	29-38	8.0-10.7	16-21
6	Powerful	39-49	10.8-13.8	22-27
7	Hard	50-61	13.9-17.1	28-33
8	stormy	62-74	17.2-20.7	34-40
9	Storm	75-88	20.8-24.4	41-47
10	Storm	89-102	24.5-28.4	48-55
11	Very heavy storm	103-117	28.5-32.6	56-63
12	Hurricane	> 117	> 32.7	> 63