// Y Stitching Measurement (v1.2)
//   Demonstration of measuring Y-Stitch error from the position difference between two gratings. 
//   Provided as-is by GenISys. 
//
//   Define Functions
//
//  compare the x positions of two features; used to sort the features into ordervar compareX = function (a, b) {
var compareX = function(a, b) { return a[0].CenterX - b[0].CenterX;}
var compareY = function(a, b) { return a[0].CenterY - b[0].CenterY;}

// compute the average of two angles in a 0-180 limited coordinate space
var avgTwoAngles = function(a) {
    if (abs(a[0] - a[1]) > 90) {
        return ((a[0] + a[1] - 180) / 2.0);
    } else {
        return ((a[0] + a[1]) / 2.0);
    }
}


//  there must be exactly four groups
if (image.length != 4) {
    "Error: Must have 4 groups."
} else {
    // extract first four groups from image, sort by coodinates of first measurements
    var groups = [0, 1, 2, 3].map(function(i) {
        return image[i];
    }).sort(compareX);
    var left = [groups[0], groups[1]].sort(compareY);
    var right = [groups[2], groups[3]].sort(compareY);

    // use convenient labels for the quadrants to be used here; the upper two quadrants
    var UL = left[1];
    var UR = right[1];

    // Check that both groups have the same number of features, give error message if not. 
    var c1 = UL.length;
    var c2 = UR.length;

    if (c1 != c2) {
        "Error: Groups must have same # of features."
    } else {
        var stsum = 0;
        //  step through each feature in the grating, compute the difference in center Y position
        //  taking rotation of the lines into account
        for (var i = 0; i < c1; i++) {
            m1 = UL[i];
            m2 = UR[i];
            var xcenter = (m1.E0CenterX + m1.E1CenterX + m2.E0CenterX + m2.E1CenterX) / 4;
            var t1 = ((m2.E0CenterY + m2.E1CenterY) / 2) + (tan(toRadians(avgTwoAngles([m2.E0Angle, m2.E1Angle]))) * (xcenter - (m2.E0CenterX + m2.E1CenterX) / 2));
            var t2 = ((m1.E0CenterY + m1.E1CenterY) / 2) + (tan(toRadians(avgTwoAngles([m1.E0Angle, m1.E1Angle]))) * (xcenter - (m1.E0CenterX + m1.E1CenterX) / 2));
            stsum = stsum + (t1 - t2);
        } // end for loop
        (stsum / c1); // the stitching error is the average of the individual line errors. 
    } // end error check for number of grating elements
} // end error check for number of groups