fPoint = {};
var xhttp = new XMLHttpRequest();
xhttp.open("GET", "/add/" + (labels.length + 1) +
"?xMin=" + xMin +
"&xMax=" + xMax +
"&yMin=" + yMin +
"&yMax=" + yMax, true);
xhttp.send();
ctx.rect(xMin, yMin, xMax - xMin, yMax - yMin);

ctx.clearRect(xMin , yMin, xMax - xMin, yMax - yMin);
ctx.lineWidth="3";
ctx.stroke();
ctx.font = "10px Arial";
ctx.fillText("id: " + id, xMin,yMin);