leaflet-geotiff-vector-arrows.js

if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
	var L = require('leaflet-geotiff');
}

L.LeafletGeotiff.VectorArrows = L.LeafletGeotiffRenderer.extend({

	options: {
		arrowSize: 20
	},

	initialize: function(options) {
		this.name = "Vector";
        L.setOptions(this, options);
	},

    setArrowSize: function (colorScale) {
        this.options.colorScale = colorScale;
        this.parent._reset();
    },
	
	render: function(raster, canvas, ctx, args) {
		var arrowSize = this.options.arrowSize;
		var gridPxelSize = (args.rasterPixelBounds.max.x - args.rasterPixelBounds.min.x) / raster.width;
		var stride = Math.max(1,Math.floor(1.2*arrowSize/gridPxelSize)); 

		for (var y=0;y<raster.height;y=y+stride) {
			for (var x=0;x<raster.width;x=x+stride) {
				var rasterIndex = (y*raster.width+x);
				if (raster.data[rasterIndex]>=0) { //Ignore missing values
					//calculate lat-lon of of this point
					var currentLng = this.parent._rasterBounds._southWest.lng + (x+0.5)*args.lngSpan;
					var currentLat = this.parent._rasterBounds._northEast.lat - (y+0.5)*args.latSpan;

					//convert lat-lon to pixel cordinates
					var projected = this.parent._map.latLngToContainerPoint(L.latLng(currentLat,currentLng)); //If slow could unpack this calculation
					var xProjected = projected.x;
					var yProjected = projected.y;

					//draw an arrow
					ctx.save();
					ctx.translate(xProjected, yProjected);
					ctx.rotate((90+raster.data[rasterIndex])*Math.PI/180);
					ctx.beginPath();
					ctx.moveTo(-arrowSize/2, 0);
					ctx.lineTo(+arrowSize/2, 0);
					ctx.moveTo(arrowSize*0.25, -arrowSize*0.25);
					ctx.lineTo(+arrowSize/2, 0);
					ctx.lineTo(arrowSize*0.25, arrowSize*0.25);
					ctx.stroke();
					ctx.restore();
				}
			}
		}
	}

});

L.LeafletGeotiff.vectorArrows= function (options) {
    return new L.LeafletGeotiff.VectorArrows(options);
};

if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
	module.exports = L.LeafletGeotiff;
}