lib/asset/htracr-ui.js
function (val) {
			var self = this;
			console.log("zooming to " + val + "...");
			self.pix_per_sec = val;
			self.render();
		}
function (val) {
			var self = this;
			console.log("zooming to " + val + "...");
			self.pix_per_sec = val;
			self.render();
		}
change the zoom level and re-render