Function unRoll

src/plots/geo/zoom.js:362–402

(rotateAngles, pt, lastRotate)

//     note that this doesn't depend on the particular projection,
//     just on the rotation angles
function unRoll(rotateAngles, pt, lastRotate) {
    // calculate the fixed point transformed by these Euler angles
    // but with the desired roll undone
    var ptRotated = rotateCartesian(pt, 2, rotateAngles[0]);
    ptRotated = rotateCartesian(ptRotated, 1, rotateAngles[1]);
    ptRotated = rotateCartesian(ptRotated, 0, rotateAngles[2] - lastRotate[2]);

    var x = pt[0];
    var y = pt[1];
    var z = pt[2];
    var f = ptRotated[0];
    var g = ptRotated[1];
    var h = ptRotated[2];

    // the following essentially solves:
    // ptRotated = rotateCartesian(rotateCartesian(pt, 2, newYaw), 1, newPitch)
    // for newYaw and newPitch, as best it can
    var theta = Math.atan2(y, x) * degrees;
    var a = Math.sqrt(x * x + y * y);
    var b;
    var newYaw1;

    if(Math.abs(g) > a) {
        newYaw1 = (g > 0 ? 90 : -90) - theta;
        b = 0;
    } else {
        newYaw1 = Math.asin(g / a) * degrees - theta;
        b = Math.sqrt(a * a - g * g);
    }

    var newYaw2 = 180 - newYaw1 - 2 * theta;
    var newPitch1 = (Math.atan2(h, f) - Math.atan2(z, b)) * degrees;
    var newPitch2 = (Math.atan2(h, f) - Math.atan2(z, -b)) * degrees;

    // which is closest to lastRotate[0,1]: newYaw/Pitch or newYaw2/Pitch2?
    var dist1 = angleDistance(lastRotate[0], lastRotate[1], newYaw1, newPitch1);
    var dist2 = angleDistance(lastRotate[0], lastRotate[1], newYaw2, newPitch2);

    if(dist1 <= dist2) return [newYaw1, newPitch1, lastRotate[2]];
    else return [newYaw2, newPitch2, lastRotate[2]];
}

function angleDistance(yaw0, pitch0, yaw1, pitch1) {
    var dYaw = angleMod(yaw1 - yaw0);