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Data Analysis Fundamentals: Math Channels

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Math Channels

03.09

00:00 - When you're just getting started with data analysis, you'll likely have more than enough information available from just the channels you're logging in order to keep you busy and find plenty of room for improvement.
00:12 As you get a little more advanced with your ability to analyse data though, you'll almost certainly get into a situation where you want to manipulate the data channels in specific ways to reveal more information.
00:24 This can be done with math channels.
00:26 In its simplest form, we can use math channels to make some basic changes to an existing channel.
00:32 Let's say for example that the steering angle sensor is calibrated so that when the steering angle moves left, the car is actually turning right.
00:41 Obviously this isn't overly intuitive and ultimately it should be fixed in the sensor calibration.
00:47 However if you already have log data, then we need to find a way to work with the situation.
00:54 We could simply use a math channel and multiply the steering angle by -1 in order to achieve our desired effect.
01:01 You'll probably notice that this can actually be dealt with by scaling the data as we previously discussed but this is a simple way of showing how a math channel actually works.
01:11 The process of creating a math channel like this is very similar across most data analysis packages and we need to start by opening the math channel editor and choosing a name for our new math channel.
01:24 In this case, we might want to call the channel steering angle corrected or something similar.
01:30 Next we want to select the units that will be associated with the new channel, which of course in this instance would be an angle.
01:38 This won't change the output but it does mean the math channel will display the appropriate units.
01:43 We can now develop the math expression that will give us the result we want.
01:47 In our case, it's as simple as multiplying the steering angle by -1.
01:53 That example is very simple, so to show you a slightly more useful application, we could look at the difference between rear wheel speed and front wheel speed to calculate a channel to show us how much wheel spin is present.
02:06 In this instance, we could use the channel name wheel slip which would be expressed as a ratio with the units of percentage.
02:14 The expression that would give us this result would require us to subtract the front wheel speed from the rear wheel speed and then divide the result by the front wheel speed.
02:24 This will give us a channel that shows the difference in wheel speed as a percentage.
02:28 In a straight line with no wheel spin we should see the result as a essentially very close to zero.
02:34 On the other hand, exiting a low speed corner where some wheel spin is present, we can see that we end up with a wheel slip in the region of 5-6%.
02:44 While this demonstrates the use of math channels in a very basic form, they can be used for much more advanced analysis that's beyond the scope of this particular course.