// X Stitching Measurement (v1.2)
//   Demonstration of measuring X-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 order
var compareX = function(a, b) {
    return a[0].CenterX - b[0].CenterX;
}
//  compare the y positions of two features; used to sort the features into order
var compareY = function(a, b) {
    return a[0].CenterY - b[0].CenterY;
}


//   must have exactly 4 groups of stored measurements. 

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 2 gratings in the lower two quadrants, using the sorted lists just created.
    var LL = left[0];
    var LR = right[0];

    // compare the spacing of the rightmost feature of the left quadrant with the leftmost feature of the right quadrant
    var m1 = LL[LL.length - 1];
    var m2 = LR[0];
    var xcenter1 = (m1.E0CenterX + m1.E1CenterX) / 2;
    var xcenter2 = (m2.E0CenterX + m2.E1CenterX) / 2;
    var xpitch = (LL.GratingPitchMean + LR.GratingPitchMean) / 2;
    //  the stitch error is the difference in this spacing from the mean grating pitch
    var xstitch = (xcenter2 - xcenter1) - xpitch;
    xstitch;
}