filter

Apply filter to tireData object data channels

Since R2024a

Syntax

obj=filter(obj,Name=Value)

Description

This function requires Extended Tire Features for Vehicle Dynamics Blockset.

obj=filter(obj,Name=Value) applies a filter specified by one or more name-value arguments to the tireData object specified by obj. The function applies a zero-phase digital filter unless you specify a moving mean to filter the data using the name-value argument k. Signal Processing Toolbox™ is required for zero-phase digital filter calculations. For more information, see filtfilt (Signal Processing Toolbox).

Note

Data channels with NaN values are not filtered.

Examples

Apply Filter to Imported Tire Data

Use the filter function to remove noise from tire measurement data. Set combinations of these name-value arguments to specify the filter design:

• k — Moving mean, where k is the window length for local k-point mean values

• d — digitalFilter object

• b, a — Transfer function coefficients

• F, Fs — Cutoff frequency and optional sampling frequency for a low-pass filter

Unless you specify a moving mean, this example requires the Signal Processing Toolbox.

Import and View Tire Measurement Data

Import tire measurement data into a tireData object, td.

td = tireData("example_data.tdx");

Multiple Fz conditions are included in the data. Use the split function to separate the data by tire data channel Fz, resulting in four tireData objects.

td = split(td,"Fz");

Use the plot function to view the normal force versus the elapsed time using the normal force to assign colors and legend values.

plot(td,DataVariableNames=["et","Fz"],ColorBy="Fz");

Specify Moving Mean

Use a moving mean to filter the data channel Fz. Set k=10.

tdFilter = filter(td,channels="Fz",k=10);

Plot the resulting tireData objects in tdFilter to visualize the modified data set.

plot(tdFilter,DataVariableNames=["et","Fz"],ColorBy="Fz");

Specify digitalFilter Object

Use the designfilt (Signal Processing Toolbox) function to create the digitalFilter object for a second-order IIR low-pass filter with HalfPowerFrequency=0.1.

d = designfilt("lowpassiir",FilterOrder=2,HalfPowerFrequency=0.1);

Filter the data channel Fz using the digitalFilter object d.

tdFilter = filter(td,channels="Fz",d=d);

Plot the resulting tireData objects in tdFilter to visualize the modified data set.

plot(tdFilter,DataVariableNames=["et","Fz"],ColorBy="Fz")

Specify Transfer Function Coefficients

Generate the b and a transfer coefficients using the butter (Signal Processing Toolbox) function.

You can use additional filter design functions can be used to generate the transfer function coefficients. For more information, see FIR Filter Design (Signal Processing Toolbox).

[b,a] = butter(2,0.1,"low");

Use the generated transfer coefficients to filter the data channel Fz.

tdFilter = filter(td,channels="Fz",b=b,a=a);

Plot the resulting tireData objects in tdFilter to visualize the modified data set.

plot(tdFilter,DataVariableNames=["et","Fz"],ColorBy="Fz")

Specify Cutoff Frequency

Set the cutoff frequency (Hz) to F=2 to use a low pass filter to filter the data channel Fz.

tdFilter = filter(td,channels="Fz",F=2);

Plot the resulting tireData objects in tdFilter to visualize the modified data set.

plot(tdFilter,DataVariableNames=["et","Fz"],ColorBy="Fz")

The cutoff frequency name-value argument uses the data channel et to calculate the sampling frequency. If et is empty or invalid for calculating the sampling frequency, additionally provide the sampling frequency Fs.

tdFilter = filter(td,channels="Fz",F=2,Fs=32);

Plot the resulting tireData objects in tdFilter to visualize the modified data set.

plot(tdFilter,DataVariableNames=["et","Fz"],ColorBy="Fz")

Input Arguments

obj — Tire data

tireData object | array of tireData objects

Tire data, specified a tireData object or an array of tireData objects.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: tdFilter = filter(td,channels="Fz",k=10);

channels — Tire data channels to filter

vector of string scalars

Tire data channels to filter, specified as a vector of string scalars. String values must be a property of the tireData object. See tireData Properties.

Note

If you do not specify channels, then the filter function filters all non-time channels.

Example: channels=["Fx", "Fy"]

Data Types: string

k — Window length for movmean

real positive scalar

Window length for movmean, specified as a real positive scalar. The movmean function is invoked by the filter function when k is specified and returns the k-point mean values. For more information, see movmean.

Example: k=10

Data Types: double

d — Digital filter

digitalFilter object

Digital filter, specified as a digitalFilter object. Use designfilt to generate a digital filter based on frequency-response specifications. For more information, see designfilt (Signal Processing Toolbox).

b,a — Transfer function coefficients

vectors

Transfer function coefficients, specified as vectors.

Example: b=[0.0201 0.0402 0.0201] and a=[1 -1.5610 0.6414]

Data Types: double

F — Cutoff frequency

scalar

Cutoff frequency, specified as a scalar, in Hz.

Note

If the tireData channel et is empty or invalid for calculating the sampling frequency, then you must provide the sampling frequency Fs.

Data Types: double

Fs — Sampling frequency

scalar

Sampling frequency, specified as a scalar, in Hz.

Note

You must provide F when specifying Fs, and you must specify Fs if the tireData channel et is empty or invalid for calculating the sampling frequency. If Fs is provided and does not match et, then the filter function uses the value of Fs for the filter design.

Data Types: double

Output Arguments

obj — Filtered tire data

tireData object | vector of tireData objects

Filtered tire data, returned as a tireData object or vector of tireData objects.

Version History

Introduced in R2024a