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title Codebook
author Agata
date 2022-11-24
output html_document

Codebook for the run_analysis.R script

Description of the variables used in analysis, copied and modified from fetures_info.txt file from the original dataset.

Variables description and units

Feature Selection

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.

  1. tBodyAcc-XYZ
  2. tGravityAcc-XYZ
  3. tBodyAccJerk-XYZ
  4. tBodyGyro-XYZ
  5. tBodyGyroJerk-XYZ
  6. tBodyAccMag
  7. tGravityAccMag
  8. tBodyAccJerkMag
  9. tBodyGyroMag
  10. tBodyGyroJerkMag
  11. fBodyAcc-XYZ
  12. fBodyAccJerk-XYZ
  13. fBodyGyro-XYZ
  14. fBodyAccMag
  15. fBodyAccJerkMag
  16. fBodyGyroMag
  17. fBodyGyroJerkMag

The set of variables that were estimated from these signals are:

  1. mean(): Mean value
  2. std(): Standard deviation
  3. mad(): Median absolute deviation
  4. max(): Largest value in array
  5. min(): Smallest value in array
  6. sma(): Signal magnitude area
  7. energy(): Energy measure. Sum of the squares divided by the number of values.
  8. iqr(): Interquartile range
  9. entropy(): Signal entropy
  10. arCoeff(): Autorregresion coefficients with Burg order equal to 4
  11. correlation(): correlation coefficient between two signals
  12. maxInds(): index of the frequency component with largest magnitude
  13. meanFreq(): Weighted average of the frequency components to obtain a mean frequency
  14. skewness(): skewness of the frequency domain signal
  15. kurtosis(): kurtosis of the frequency domain signal
  16. bandsEnergy(): Energy of a frequency interval within the 64 bins of the FFT of each window.
  17. angle(): Angle between to vectors.

Additional vectors obtained by averaging the signals in a signal window sample. These are used on the angle() variable:

gravityMean tBodyAccMean tBodyAccJerkMean tBodyGyroMean tBodyGyroJerkMean

From the original datasets only the values of the mean and standard deviation (std) for the measurements were extracted.

List of variables in the tidy dataset:

  1. dataset
  2. subject
  3. activity
  4. tBodyAccmeanX
  5. tBodyAccmeanY
  6. tBodyAccmeanZ
  7. tGravityAccmeanX
  8. tGravityAccmeanY
  9. tGravityAccmeanZ
  10. tBodyAccJerkmeanX
  11. tBodyAccJerkmeanY
  12. tBodyAccJerkmeanZ
  13. tBodyGyromeanX
  14. tBodyGyromeanY
  15. tBodyGyromeanZ
  16. tBodyGyroJerkmeanX
  17. tBodyGyroJerkmeanY
  18. tBodyGyroJerkmeanZ
  19. tBodyAccMagmean
  20. tGravityAccMagmean
  21. tBodyAccJerkMagmean
  22. tBodyGyroMagmean
  23. tBodyGyroJerkMagmean
  24. fBodyAccmeanX
  25. fBodyAccmeanY
  26. fBodyAccmeanZ
  27. fBodyAccmeanFreqX
  28. fBodyAccmeanFreqY
  29. fBodyAccmeanFreqZ
  30. fBodyAccJerkmeanX
  31. fBodyAccJerkmeanY
  32. fBodyAccJerkmeanZ
  33. fBodyAccJerkmeanFreqX
  34. fBodyAccJerkmeanFreqY
  35. fBodyAccJerkmeanFreqZ
  36. fBodyGyromeanX
  37. fBodyGyromeanY
  38. fBodyGyromeanZ
  39. fBodyGyromeanFreqX
  40. fBodyGyromeanFreqY
  41. fBodyGyromeanFreqZ
  42. fBodyAccMagmean
  43. fBodyAccMagmeanFreq
  44. fBodyBodyAccJerkMagmean
  45. fBodyBodyAccJerkMagmeanFreq
  46. fBodyBodyGyroMagmean
  47. fBodyBodyGyroMagmeanFreq
  48. fBodyBodyGyroJerkMagmean
  49. fBodyBodyGyroJerkMagmeanFreq
  50. angletBodyAccMean.gravity
  51. angletBodyAccJerkMean.gravityMean
  52. angletBodyGyroMean.gravityMean
  53. angletBodyGyroJerkMean.gravityMean
  54. angleX.gravityMean
  55. angleY.gravityMean
  56. angleZ.gravityMean
  57. tBodyAccstdX
  58. tBodyAccstdY
  59. tBodyAccstdZ
  60. tGravityAccstdX
  61. tGravityAccstdY
  62. tGravityAccstdZ
  63. tBodyAccJerkstdX
  64. tBodyAccJerkstdY
  65. tBodyAccJerkstdZ
  66. tBodyGyrostdX
  67. tBodyGyrostdY
  68. tBodyGyrostdZ
  69. tBodyGyroJerkstdX
  70. tBodyGyroJerkstdY
  71. tBodyGyroJerkstdZ
  72. tBodyAccMagstd
  73. tGravityAccMagstd
  74. tBodyAccJerkMagstd
  75. tBodyGyroMagstd
  76. tBodyGyroJerkMagstd
  77. fBodyAccstdX
  78. fBodyAccstdY
  79. fBodyAccstdZ
  80. fBodyAccJerkstdX
  81. fBodyAccJerkstdY
  82. fBodyAccJerkstdZ
  83. fBodyGyrostdX
  84. fBodyGyrostdY
  85. fBodyGyrostdZ
  86. fBodyAccMagstd
  87. fBodyBodyAccJerkMagstd
  88. fBodyBodyGyroMagstd
  89. fBodyBodyGyroJerkMagstd