The features selected for this database come from the accelerometer and gyroscope 3-axial raw signals tAcc-XYZ and tGyro-XYZ. These time domain signals (prefix 't' to denote time) were captured at a constant rate of 50 Hz. Then they were filtered using a median filter and a 3rd order low pass Butterworth filter with a corner frequency of 20 Hz to remove noise. Similarly, the acceleration signal was then separated into body and gravity acceleration signals (tBodyAcc-XYZ and tGravityAcc-XYZ) using another low pass Butterworth filter with a corner frequency of 0.3 Hz.
Subsequently, the body linear acceleration and angular velocity were derived in time to obtain Jerk signals (tBodyAccJerk-XYZ and tBodyGyroJerk-XYZ). Also the magnitude of these three-dimensional signals were calculated using the Euclidean norm (tBodyAccMag, tGravityAccMag, tBodyAccJerkMag, tBodyGyroMag, tBodyGyroJerkMag).
Finally a Fast Fourier Transform (FFT) was applied to some of these signals producing fBodyAcc-XYZ, fBodyAccJerk-XYZ, fBodyGyro-XYZ, fBodyAccJerkMag, fBodyGyroMag, fBodyGyroJerkMag. (Note the 'f' to indicate frequency domain signals).
These signals were used to estimate variables of the feature vector for each pattern:
'-XYZ' is used to denote 3-axial signals in the X, Y and Z directions.
- tBodyAcc-XYZ
- tGravityAcc-XYZ
- tBodyAccJerk-XYZ
- tBodyGyro-XYZ
- tBodyGyroJerk-XYZ
- tBodyAccMag
- tGravityAccMag
- tBodyAccJerkMag
- tBodyGyroMag
- tBodyGyroJerkMag
- fBodyAcc-XYZ
- fBodyAccJerk-XYZ
- fBodyGyro-XYZ
- fBodyAccMag
- fBodyAccJerkMag
- fBodyGyroMag
- fBodyGyroJerkMag
The set of variables that were estimated from these signals are:
- mean(): Mean value
- std(): Standard deviation
- meanFreq(): Weighted average of the frequency components to obtain a mean
Additional vectors obtained by averaging the signals in a signal window sample. These are used on the angle() variable:
- gravityMean
- tBodyAccMean
- tBodyAccJerkMean
- tBodyGyroMean
- tBodyGyroJerkMean
The fields are means of all of the values in the original raw data -- calculated for each activity/subject pair:
| column name | units | description |
|---|---|---|
| activity.name | none | descriptive name of the activity |
| subject | none | which lab subject performed the activity (values = 1-30) |
| activity.code | none | code for the activity (values = 1-6) |
| tBodyAcc-mean()-X | g | average of mean body linear acceleration on x-axis |
| tBodyAcc-mean()-Y | g | average of mean body linear acceleration on y-axis |
| tBodyAcc-mean()-Z | g | average of mean body linear acceleration on z-axis |
| tBodyAcc-std()-X | g | average of std deviation of body linear acceleration on x-axis |
| tBodyAcc-std()-Z | g | average of std deviation of body linear acceleration on z-axis |
| tBodyAcc-std()-Y | g | average of std deviation of body linear acceleration on y-axis |
| tGravityAcc-mean()-X | g | average of mean gravity acceleration on x axis |
| tGravityAcc-mean()-Y | g | average of mean gravity acceleration on y axis |
| tGravityAcc-mean()-Z | g | average of mean gravity acceleration on z axis |
| tGravityAcc-std()-X | g | average of standard deviation for gravity acceleration on x axis |
| tGravityAcc-std()-Y | g | average of standard deviation for gravity acceleration on y axis |
| tGravityAcc-std()-Z | g | average of standard deviation for gravity acceleration on z axis |
| tBodyAccJerk-mean()-X | g | average of mean for jerk body acceleration on x axis |
| tBodyAccJerk-mean()-Y | g | average of mean for jerk body acceleration on y axis |
| tBodyAccJerk-mean()-Z | g | average of mean for jerk body acceleration on z axis |
| tBodyAccJerk-std()-X | g | average of standard deviation for jerk body acceleration on x axis |
| tBodyAccJerk-std()-Y | g | average of standard deviation for jerk body acceleration on y axis |
| tBodyAccJerk-std()-Z | g | average of standard deviation for jerk body acceleration on z axis |
| tBodyGyro-mean()-X | radians/second | average of mean for body gyro angular velocity on x axis |
| tBodyGyro-mean()-Y | radians/second | average of mean for body gyro angular velocity on y axis |
| tBodyGyro-mean()-Z | radians/second | average of mean for body gyro angular velocity on z axis |
| tBodyGyro-std()-X | radians/second | average of standard deviation for body gyro angular velocity on x axis |
| tBodyGyro-std()-Y | radians/second | average of standard deviation for body gyro angular velocity on y axis |
| tBodyGyro-std()-Z | radians/second | average of standard deviation for body gyro angular velocity on z axis |
| tBodyGyroJerk-mean()-X | radians/second | average of mean for body gyro jerk angular velocity on x axis |
| tBodyGyroJerk-mean()-Y | radians/second | average of mean for body gyro jerk angular velocity on y axis |
| tBodyGyroJerk-mean()-Z | radians/second | average of mean for body gyro jerk angular velocity on z axis |
| tBodyGyroJerk-std()-X | radians/second | average of standard deviation for body gyro jerk angular velocity on x axis |
| tBodyGyroJerk-std()-Y | radians/second | average of standard deviation for body gyro jerk angular velocity on y axis |
| tBodyGyroJerk-std()-Z | radians/second | average of standard deviation for body gyro jerk angular velocity on z axis |
| tBodyAccMag-mean() | g | average of mean magnitude of 3D body acceleration signals |
| tBodyAccMag-std() | g | average of standard deviation of magnitude of 3D body acceleration signals |
| tGravityAccMag-mean() | g | average of mean magnitude of 3D gravity acceleration signals |
| tGravityAccMag-std() | g | average of standard deviation of magnitude of 3D gravity acceleration signals |
| tBodyAccJerkMag-mean() | g | average of mean magnitude of 3D jerk acceleration signals |
| tBodyAccJerkMag-std() | g | average of standard deviation of magnitude of 3D jerk acceleration signals |
| tBodyGyroMag-mean() | radians/second | average of mean magnitude of 3D body angular velocity |
| tBodyGyroMag-std() | radians/second | average of standard deviation of magnitude of 3D body angular velocity |
| tBodyGyroJerkMag-mean() | radians/second | average of mean magnitude of 3D jerk angular velocity |
| tBodyGyroJerkMag-std() | radians/second | average of standard deviation of magnitude of 3D jerk angular velocity |
| fBodyAcc-mean()-X | g | average of mean FFT of body linear acceleration on x-axis |
| fBodyAcc-mean()-Y | g | average of mean FFT of body linear acceleration on y-axis |
| fBodyAcc-mean()-Z | g | average of mean FFT of body linear acceleration on z-axis |
| fBodyAcc-std()-X | g | average of std deviation of FFT of body linear acceleration on x-axis |
| fBodyAcc-std()-Y | g | average of std deviation of FFT of body linear acceleration on z-axis |
| fBodyAcc-std()-Z | g | average of std deviation of FFT of body linear acceleration on y-axis |
| fBodyAccJerk-mean()-X | g | average of mean FFT for jerk body acceleration on x axis |
| fBodyAccJerk-mean()-Y | g | average of mean FFT for jerk body acceleration on y axis |
| fBodyAccJerk-mean()-Z | g | average of mean FFT for jerk body acceleration on z axis |
| fBodyAccJerk-std()-X | g | average of standard deviation of FFT for jerk body acceleration on x axis |
| fBodyAccJerk-std()-Y | g | average of standard deviation of FFT for jerk body acceleration on y axis |
| fBodyAccJerk-std()-Z | g | average of standard deviation of FFT for jerk body acceleration on z axis |
| fBodyGyro-mean()-X | radians/second | average of mean FFT for body gyro angular velocity on x axis |
| fBodyGyro-mean()-Y | radians/second | average of mean FFT for body gyro angular velocity on y axis |
| fBodyGyro-mean()-Z | radians/second | average of mean FFT for body gyro angular velocity on z axis |
| fBodyGyro-std()-X | radians/second | average of standard deviation of FFT for body gyro angular velocity on x axis |
| fBodyGyro-std()-Y | radians/second | average of standard deviation of FFT for body gyro angular velocity on y axis |
| fBodyGyro-std()-Z | radians/second | average of standard deviation of FFT for body gyro angular velocity on z axis |
| fBodyAccMag-mean() | g | average of mean FFT of magnitude of 3D body acceleration signals |
| fBodyAccMag-std() | g | average of standard deviation of FFT of magnitude of 3D body acceleration signals |
| fBodyBodyAccJerkMag-mean() | g | average of mean magnitude of FFT of 3D gravity acceleration signals |
| fBodyBodyAccJerkMag-std() | g | average of standard deviation of FFT of magnitude of 3D gravity acceleration signals |
| fBodyBodyGyroMag-mean() | radians/second | average of mean magnitude of FFT of 3D jerk acceleration signals |
| fBodyBodyGyroMag-std() | radians/second | average of standard deviation of FFT of magnitude of 3D jerk acceleration signals |
| fBodyBodyGyroJerkMag-mean() | radians/second | average of mean magnitude of FFT of 3D jerk acceleration signals |
| fBodyBodyGyroJerkMag-std() | radians/second | average of standard deviation of FFT of magnitude of 3D jerk acceleration signals |