MATLAB Examples

Human Activity Learning Using Mobile Phone Data

Human activity sensor data contains observations derived from sensor measurements taken from smartphones worn by people while doing different activities (walking, lying, sitting etc). The goal of this example is to provide a strategy to build a classifier that can automatically identify the activity type given the sensor measurements.

Copyright (c) 2015, MathWorks, Inc.

Contents

Description of the Data

The dataset consists of accelerometer and gyroscope data captured at
50Hz. The raw sensor data contain fixed-width sliding windows of 2.56 sec
(128 readings/window). The activities performed by the subject include:
'Walking', 'ClimbingStairs', 'Sitting', 'Standing',and 'Laying'

How to get the data: Execute downloadSensorData and follow the instructions to download the and extract the data from the source webpage. After the files have been extracted run saveSensorDataAsMATFiles. This will create two MAT files: rawSensorData_train and rawSensorData_test with the raw sensor data

  1. total_acc_(x/y/z)_train : Raw accelerometer sensor data
  2. body_gyro_(x/y/z)_train : Raw gyroscope sensor data
  3. trainActivity : Training data labels
  4. testActivity : Test data labels

Reference:

Davide Anguita, Alessandro Ghio, Luca Oneto, Xavier Parra and Jorge L. Reyes-Ortiz. Human Activity Recognition on Smartphones using a Multiclass Hardware-Friendly Support Vector Machine. International Workshop of Ambient Assisted Living (IWAAL 2012). Vitoria-Gasteiz, Spain. Dec 2012

Download data from source

If you are running this script for the first time, make sure that you
execute these functions.
  • downloadSensorData : This function will download the dataset and extract its contents to a folder called: UCI HAR Dataset This folder must be present before you execute saveSensorDataAsMATFiles
if ~exist('UCI HAR Dataset','file')
    downloadSensorData;
end

Load data frome individual files and save as MAT file for reuse

  • saveSensorDataAsMATFiles : This function will load the data from the individual source files and save the data in a single MAT file for easy accesss
if ~exist('rawSensorData_train.mat','file') && ~exist('rawSensorData_test.mat','file')
    saveSensorDataAsMATFiles;
end

Load Training Data

load rawSensorData_train

Display data summary

plotRawSensorData(total_acc_x_train, total_acc_y_train, ...
    total_acc_z_train,trainActivity,1000)

Create Table variable

rawSensorDataTrain = table(...
    total_acc_x_train, total_acc_y_train, total_acc_z_train, ...
    body_gyro_x_train, body_gyro_y_train, body_gyro_z_train);

Pre-process Training Data: Feature Extraction

Lets start with a simple preprocessing technique. Since the raw sensor data contain fixed-width sliding windows of 2.56sec (128 readings/window) lets start with a simple average feature for every 128 points

humanActivityData = varfun(@Wmean,rawSensorDataTrain);
humanActivityData.activity = trainActivity;

Train a model and assess its performance using Classification Learner

classificationLearner

Additional Feature Extraction

T_mean = varfun(@Wmean, rawSensorDataTrain);
T_stdv = varfun(@Wstd,rawSensorDataTrain);
T_pca  = varfun(@Wpca1,rawSensorDataTrain);

humanActivityData = [T_mean, T_stdv, T_pca];
humanActivityData.activity = trainActivity;

Use the new features to train a model and assess its performance

classificationLearner

Load Test Data

load rawSensorData_test

Visualize classifier performance on test data

Step 1: Create a table

rawSensorDataTest = table(...
    total_acc_x_test, total_acc_y_test, total_acc_z_test, ...
    body_gyro_x_test, body_gyro_y_test, body_gyro_z_test);

% Step 2: Extract features from raw sensor data
T_mean = varfun(@Wmean, rawSensorDataTest);
T_stdv = varfun(@Wstd,rawSensorDataTest);
T_pca  = varfun(@Wpca1,rawSensorDataTest);

humanActivityData = [T_mean, T_stdv, T_pca];
humanActivityData.activity = testActivity;

% Step 3: Use trained model to predict activity on new sensor data
% Make sure that you've exported 'trainedClassifier' from
% ClassificationLearner
plotActivityResults(trainedClassifier,rawSensorDataTest,humanActivityData,0.1)