Explanation: TrailRunner can display the maximum speed value from either the imported workout data (if available) or can calculate the value by an analysis of your workout data.
On statistical aggregates
If your GPS Device has lost its signal and re-catches it, the recoded course may contain errors. This error may lead to unrealistic values as such signal jumps may assume you where moving faster that light. Therefore TrailRunner uses a low-pass filter of roughly 90% and takes the highest value within the result as your maximum speed. To turn this off, uncheck the calculate statistical aggregates option.
On split intervals
The horizontal interval size slider controls the size of interval splits.
The intervals are being displayed as white lines in the graph, each containing a white circle on the value that was most common within this interval.
In addition the lowest values and the highest values within this interval are being displayed as a dot bordered gray region.
The overall maximum speed of an activity is the maximum speed from all these split intervals.
As this is a statistical calculation, the values may vary when you change the size of the split intervals. The bigger the intervals, any filtering becomes stronger.
Problem: As depicted in the screenshot above, TrailRunner sometimes cuts off high values within a chart.
Background: To analyze a workout, the most interesting part of the chart is the area your workout did spend the most time in. If your GPS signal was weak and produced a noise peak, this single error would decrease the vertical resolution of your graph and therefore would make it unreadable. For this reason TrailRunner cuts off the chart for everything that is located outside of approximately 90% of your data points.
Customizing: To customize this behavior, you can control the display range under TrailRunner > Preferences > Advanced > Chart : Vertical exaggeration.
Problem: As depicted in the second screenshot above, the head or tail of a chart may not be displayed.
Background: The chart above displays a statistical trend. This means that TrailRunner takes all data points available, creates a set of intervals (in this case one month per each interval) and then displays a representative data point for this interval. The representative is the value that had the highest statistical appearance within the interval (mathematically this is called a median, not average). Then a data point is being displayed at the location of the representative. As this is almost never at the beginning or the end of the interval the graph seems to be cut off.
Sidenote: Please also note the gray border around the graph lines. The border depicts the maximum and the minimum values within each interval. So the graph gives you a good overall picture on the trend including extreme values. All data points are located within the gray area and the most frequent values are depicted by the colored line.
Solution: Select the diary entries in TrailRunner and use Edit > Copy to paste the data into an external spreadsheet application like Numbers or Excel. To select all entries in TrailRunner, use Command-A.
Tip: If you import your data into Excel, make sure that the column separator is set to "tab separated".
Background: Other applications display the raw data of a device. This makes the graph unreadable. The philosophy of TrailRunner instead is to display the overall trend and development of your workout session.
Approach: TrailRunner has an auto split feature where the workout is being sliced into fixed distance intervals. For each interval the statistical median value is being calculated and one data point reflecting this value is then being used as a representative. As the location of the representative can be somewhere in-between the first interval, the graph might appear to be indented. Furthermore if representatives in adjacent intervals fall onto a straight line, only the edges representatives are being drawn and the connection line depicts the trend development.
Details: The auto split feature uses the following distance intervals. By the time of this writing it’s 250 m for workouts shorter than 10 km, then 500m up to 20 km, 1000 m up to 50 km and 10000 m from there on. A route with 42 km would then have 5 intervals.
Example: Below the identical workout in Garmin Training Center (upper image) and TrailRunner (lower image)
It’s rather obvious that the speed Graph in Garmin Training Center is full of noise and false signals. TrailRunner filters this out and gives you the statistical trend (blue line) for each interval (white circle within each interval separated by a white vertical line)
The thinner line around the blue line depicts the value range, so you still can make up that within the interval there was a great spread of values, but most of the time you stayed near the value depicted by the thick line.
BTW please note that the Garmin speed graph is upside down, so slower is a value near the top and faster is a value near the end. TrailRunner uses a the natural, mirrored display approach, where “better” is on top.
Background: During the workout, your ForeRunner records geographical data points. At the same time your ForeRunner internally adds up the distances as a total distance so far. If you have intelligent recording enabled on your ForeRunner and the GPS signal quality isn't too good, the device will alter the recorded geographical course -- and therefore the derived distance -- after it knows better. Problem is that at the same time the overall distance should also be adjusted, which is not the case.
Status: To avoid confusion, TrailRunner usually displays the distance your device is displaying. But it could happen that the real distance, based on the mere data points, "slips through" in TrailRunner. This indeed is contradictory information but at the same time it is like impossible to me to "do it right".