subtendedAngle: Subtended Angle
In eyetracking: Eyetracking Helper Functions

Description Usage Arguments Value Author(s) Examples

Takes two screen coordinates and returns the angle (in degrees) subtended by those two points.

1	subtendedAngle(x1, y1, x2, y2, viewerDistance = 58.74, viewerHeight = 4.55, resolutionX = 1280, resolutionY = 1024, screenWidth = 33.97, screenHeight = 27.31)

`x1`	The x coordinate of the first point on a screen
`y1`	The y coordinate of the first point on a screen
`x2`	The x coordinate of the second point on a screen
`y2`	The y coordinate of the second point on a screen
`viewerDistance`	Perpendicular distance from the viewer to the screen (cm)
`viewerHeight`	Vertical height of the viewer above screen center (cm)
`resolutionX`	The x resolution of the monitor (pixels)
`resolutionY`	The y resolution of the monitor (pixels)
`screenWidth`	The physical screen width (cm)
`screenHeight`	The physical screen height (cm)

The angle (in degrees) subtended by two points

Ryan M. Hope

function( x1, y1, x2, y2, viewerDistance=58.74, viewerHeight=4.55, resolutionX=1280, resolutionY=1024, screenWidth=33.97, screenHeight=27.31 ) {
    
    d1 <- distance2point(x1, y1, viewerDistance, viewerHeight, resolutionX, resolutionY, screenWidth, screenHeight)
    d2 <- distance2point(x2, y2, viewerDistance, viewerHeight, resolutionX, resolutionY, screenWidth, screenHeight)
    
    dX <- screenWidth * ( x2 - x1 ) / resolutionX
    dY <- screenWidth * ( y2 - y1 ) / resolutionY
    
    screenDistance <- sqrt( dX^2 + dY^2 )
    
    angleRadians <- acos( ( d1^2 + d2^2 - screenDistance^2 ) / ( 2 * d1 * d2 ) )
    
    angleRadians / ( 2 * pi ) * 360
    
  }