This file describes the variable in each column of the tidy data.
- subject
It identifies the subject who performed the activity. Its range is from 1 to 30.
- activity
It identifies the activity performed by the subject. There are 6 possible activities: walking, walking_upstairs, walking_downstairs, sitting, standing, laying
The remaning 66 variables represent for each subject and for each activity the average over all time windows of the mean and standard deviation of the taken measurements. The measurements selected 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. The list of these variable is the following:
3 tBodyAccmeanX
4 tBodyAccmeanY
5 tBodyAccmeanZ
6 tBodyAccstdX
7 tBodyAccstdY
8 tBodyAccstdZ
9 tGravityAccmeanX
10 tGravityAccmeanY
11 tGravityAccmeanZ
12 tGravityAccstdX
13 tGravityAccstdY
14 tGravityAccstdZ
15 tBodyAccJerkmeanX
16 tBodyAccJerkmeanY
17 tBodyAccJerkmeanZ
18 tBodyAccJerkstdX
19 tBodyAccJerkstdY
20 tBodyAccJerkstdZ
21 tBodyGyromeanX
22 tBodyGyromeanY
23 tBodyGyromeanZ
24 tBodyGyrostdX
25 tBodyGyrostdY
26 tBodyGyrostdZ
27 tBodyGyroJerkmeanX
28 tBodyGyroJerkmeanY
29 tBodyGyroJerkmeanZ
30 tBodyGyroJerkstdX
31 tBodyGyroJerkstdY
32 tBodyGyroJerkstdZ
33 tBodyAccMagmean
34 tBodyAccMagstd
35 tGravityAccMagmean
36 tGravityAccMagstd
37 tBodyAccJerkMagmean
38 tBodyAccJerkMagstd
39 tBodyGyroMagmean
40 tBodyGyroMagstd
41 tBodyGyroJerkMagmean
42 tBodyGyroJerkMagstd
43 fBodyAccmeanX
44 fBodyAccmeanY
45 fBodyAccmeanZ
46 fBodyAccstdX
47 fBodyAccstdY
48 fBodyAccstdZ
49 fBodyAccJerkmeanX
50 fBodyAccJerkmeanY
51 fBodyAccJerkmeanZ
52 fBodyAccJerkstdX
53 fBodyAccJerkstdY
54 fBodyAccJerkstdZ
55 fBodyGyromeanX
56 fBodyGyromeanY
57 fBodyGyromeanZ
58 fBodyGyrostdX
59 fBodyGyrostdY
60 fBodyGyrostdZ
61 fBodyAccMagmean
62 fBodyAccMagstd
63 fBodyBodyAccJerkMagmean
64 fBodyBodyAccJerkMagstd
65 fBodyBodyGyroMagmean
66 fBodyBodyGyroMagstd
67 fBodyBodyGyroJerkMagmean
68 fBodyBodyGyroJerkMagstd