05 - Circuit Tools Graph Window
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The graph window shows the logged channels in the form of a plot against distance, time or position. The speed channel is normally shown at the top.
The value of the channel at the cursor position is shown in the Data window. The data traces and channel values both use the same colour. By default the faster lap has a red trace.
Zooming and panning the Graph window
The quickest way to zoom in the Graph Window is to draw a zoom box with the left hand mouse button from the left to the right. To zoom out, simply draw a box from the right to the left. You can also use the up and down arrow keys.
To pan, use the right hand mouse button and drag the graph either way, or use CTRL and the cursor keys.
There are also buttons on the menu tab and just above the graph.
Delta-T (Lap-time difference)
By far the most useful parameter for comparing Laps is the Delta-T channel. Delta-T is the running lap-time difference between two laps and gives a very clear indication of where time is lost or gained around the circuit.
When the Delta-T is increasing, time is being lost, and when it is decreasing, time is being gained.
At first, look for the largest changes in Delta-T and concentrate on these areas.
Sometimes, in a corner there may be a large gain followed by a large loss. This often happens when you enter a corner faster, but exit more slowly.
It is often surprising how much time you lose down the straight by exiting a corner a little bit slower than before.
By zooming into a section, the Delta-T is reset to zero for the start of that section, making it easier for you to analyse a local area of the track.
Changing the zoom mode in the Graph window
By default the zoom only affects the X-axis, this can be changed by using the buttons in the Graph Ribbon menu. By allowing zoom in both axes you can magnify the graph in more detail.
Lap alignment - Distance vs. Position
There are three ways of aligning comparison data: Time, Distance and Position. Position is the default X axis and this is the method recommended for comparing two different laps. Time and distance are only used in special circumstances.
Traditionally, rolling distance has been used to align laps, but with the advent of GPS, it is better to use GPS position, as the distance travelled around a lap varies from lap to lap depending on the driving line. The position remains more accurate, as the error in GPS is much less than the variation in rolling distance (often >30m).
A comparison of this effect can be seen below from two different professional drivers at the Nordschleife during a race. The first plot uses the rolling distance to compare the two drivers, and the second uses GPS position. In the first plot they have both travelled exactly 19785m from the Start / Finish line, but are now 186m apart! In the second plot the GPS position of each vehicle is used to align the traces, and here you can see how closely they now line up.
Using GPS Position alignment also makes the Delta-T value very accurate, which makes the values meaningful even around the Nordschleife, where a Delta-T or predictive lap-timer based on distance would only be accurate to around 1-2s after a full lap.
Using Position, the Delta-T and Racelogic Predictive Lap-Timer are accurate to within 0.02s around the full length of the Nordschleife!
Note: Graphing using this method relies on good GPS position data. If you lose GPS position or you have heavy tree cover, then it is best to switch back to distance or even Time. If you leave the track, or cut out a part of the circuit, then again you will get a very poor position based comparison or you may even be unable to play the video or move the graph cursor beyond the point where you left the circuit if a poor datum is used.