Simple PHP implementation of the "Andrew's Monotone Chain" convex hull algorithm
$input = [
[ -1.4227294921875, 52.19413974159753 ],
[ -2.1148681640624996, 51.88666357770388 ],
[ -1.69189453125, 51.879882095410224 ],
[ -2.0709228515625, 51.2928411273273 ],
[ -1.1151123046875, 51.155231611562265 ],
[ -1.4666748046875, 51.57706953722567 ],
[ -0.5548095703125, 51.64870258356996 ],
[ -1.1920166015625, 51.84595933666338 ],
[ -0.648193359375, 52.11325243469631 ],
[ -1.285400390625, 52.55965567958736 ],
[ -1.4227294921875, 52.19413974159753 ]
];
$output = convexHull($input);
/*
-2.11486816406, 51.8866635777
-2.07092285156, 51.2928411273
-1.11511230469, 51.1552316116
-0.554809570312, 51.6487025836
-0.648193359375, 52.1132524347
-1.28540039062, 52.5596556796
-2.11486816406, 51.8866635777
*/