How to draw a polygon around a polyline in JavaScript?

I want to draw a polygon around a polyline. The polyline in my case is a Google Maps direction and I need to show a polygon around it within the Google Maps canvas.

First:

For offsetting I use the JavaScript Clipper Library. I have the following polyline (route): I make an offset polygon below using Clipper:

I have a working JS Bin example.

The code is:

<html>
  <head>
    <title>Javascript Clipper Library / Offset polyline</title>
    <script src="clipper.js"></script>
    <script>
    function draw() {
      var polygons = [[{"X":72,"Y":59.45},{"X":136,"Y":66},{"X":170,"Y":99},{"X":171,"Y":114},{"X":183,"Y":125},{"X":218,"Y":144},{"X":218,"Y":165},{"X":226,"Y":193},{"X":254,"Y":195},{"X":283,"Y":195},{"X":292,"Y":202},{"X":325,"Y":213},{"X":341,"Y":234},{"X":397,"Y":245},{"X":417,"Y":248}]]; 
      var scale = 100;
      reverse_copy(polygons);
      polygons = scaleup(polygons, scale);
      var cpr = new ClipperLib.Clipper();
      var delta = 25;
      var joinType = ClipperLib.JoinType.jtRound;
      var miterLimit = 2;
      var AutoFix = true;
      var svg, offsetted_polygon,
      cont = document.getElementById('svgcontainer');
      offsetted_polygon = cpr.OffsetPolygons(polygons, delta * scale, joinType, miterLimit, AutoFix);
      //console.log(JSON.stringify(offsetted_polygon));

      // Draw red offset polygon
      svg = '<svg style="margin-top:10px;margin-right:10px;margin-bottom:10px;background-color:#dddddd" width="540" height="340">';
      svg += '<path stroke="red" fill="red" stroke-width="2" stroke-opacity="0.6" fill-opacity="0.2" d="' + polys2path(offsetted_polygon, scale) + '"/>';

      //Draw blue polyline
      svg += '<path stroke="blue" stroke-width="3" d="' + polys2path(polygons, scale) + '"/>';
      svg += '</svg>';

      cont.innerHTML += svg;
    }

    // helper function to scale up polygon coordinates
    function scaleup(poly, scale) {
      var i, j;

      if (!scale)
        scale = 1;

      for(i = 0; i < poly.length; i++) {
        for(j = 0; j < poly[i].length; j++) {
          poly[i][j].X *= scale;
          poly[i][j].Y *= scale;
        }
      }

      return poly;
    }

    // converts polygons to SVG path string
    function polys2path (poly, scale) {
      var path = "", i, j;

      if (!scale)
        scale = 1;

      for(i = 0; i < poly.length; i++) {
        for(j = 0; j < poly[i].length; j++) {
          if (!j)
            path += "M";
          else
            path += "L";
          path += (poly[i][j].X / scale) + ", " + (poly[i][j].Y / scale);
        }
        path += "Z";
      }

      return path;
    }

    function reverse_copy(poly) {
      // Make reverse copy of polygons = convert polyline to a 'flat' polygon ...
      var k, klen = poly.length, len, j; 

      for (k = 0; k < klen; k++) {
        len = poly[k].length;
        poly[k].length = len * 2 - 2;

        for (j = 1; j <= len - 2; j++) {
          poly[k][len - 1 + j] = {
            X: poly[k][len - 1 - j].X,
            Y: poly[k][len - 1 - j].Y
          }
        }
      }
    }
    </script>
  </head>
  <body onload="draw()">
    <h2>Javascript Clipper Library / Offset polyline</h2>
    This page shows an example of offsetting polyline and drawing it using SVG.
    <div id="svgcontainer"></div>
  </body>
</html>

And all this is good but now I must replace the polygon variables with points from Google Maps directions, so I do this change:

directionsService.route(request, function(response, status) {
  if (status == google.maps.DirectionsStatus.OK) {
    directionsDisplay.setDirections(response);

    function draw() {
      var polygons = response.routes[0].overview_path; 

      //REST OF CODE
    }
  }
}

I have a JS Bin example with this code for offsetting the polygon around the polyline.

But there is some problem, which I can't regonize and I can't get a polygon around directions.

Is there any way to solve this problem?

Solution 1:

My working solution: working example (based off of Manolis Xountasis's answer) and pieces from these related questions:

How to calculate intersection area in Google Maps API with JSTS Library?
Google Maps Polygons self intersecting detection

include the JSTS library
add routines to translate google.maps.Polyline paths to JSTS objects:

function googleMaps2JTS(boundaries) {
    var coordinates = [];
    var length = 0;
    if (boundaries && boundaries.getLength) length = boundaries.getLength();
    else if (boundaries && boundaries.length) length = boundaries.length;
    for (var i = 0; i < length; i++) {
        if (boundaries.getLength) coordinates.push(new jsts.geom.Coordinate(
        boundaries.getAt(i).lat(), boundaries.getAt(i).lng()));
        else if (boundaries.length) coordinates.push(new jsts.geom.Coordinate(
        boundaries[i].lat(), boundaries[i].lng()));
    }
    return coordinates;
};

and back to google.maps.LatLng arrays

var jsts2googleMaps = function (geometry) {
  var coordArray = geometry.getCoordinates();
  GMcoords = [];
  for (var i = 0; i < coordArray.length; i++) {
    GMcoords.push(new google.maps.LatLng(coordArray[i].x, coordArray[i].y));
  }
  return GMcoords;
}

get the directions polyline from the DirectionsService and buffer it

directionsService.route(request, function (response, status) {
    if (status == google.maps.DirectionsStatus.OK) {
        directionsDisplay.setDirections(response);
        var overviewPath = response.routes[0].overview_path,
            overviewPathGeo = [];
        for (var i = 0; i < overviewPath.length; i++) {
            overviewPathGeo.push(
            [overviewPath[i].lng(), overviewPath[i].lat()]);
        }

        var distance = 10 / 111.12, // Roughly 10km
            geoInput = {
                type: "LineString",
                coordinates: overviewPathGeo
            };
        var geoInput = googleMaps2JTS(overviewPath);
        var geometryFactory = new jsts.geom.GeometryFactory();
        var shell = geometryFactory.createLineString(geoInput);
        var polygon = shell.buffer(distance);

        var oLanLng = [];
        var oCoordinates;
        oCoordinates = polygon.shell.points[0];
        for (i = 0; i < oCoordinates.length; i++) {
            var oItem;
            oItem = oCoordinates[i];
            oLanLng.push(new google.maps.LatLng(oItem[1], oItem[0]));
        }
        if (routePolygon && routePolygon.setMap) routePolygon.setMap(null);
        routePolygon = new google.maps.Polygon({
            paths: jsts2googleMaps(polygon),
            map: map
        });
    }
});

screenshot of resulting map

Solution 2:

This is the working solution. You can find the JSTS files at coderwall.com.

var overviewPath = response.routes[0].overview_path,
overviewPathGeo = [];
for (var i = 0; i < overviewPath.length; i++) {
   overviewPathGeo.push(
      [overviewPath[i].lng(), overviewPath[i].lat()]
   );
}

var distance = value / 10000, // Roughly 10km
geoInput = {
type: "LineString",
    coordinates: overviewPathGeo
};
var geoReader = new jsts.io.GeoJSONReader(),
    geoWriter = new jsts.io.GeoJSONWriter();
var geometry = geoReader.read(geoInput).buffer(distance);
var polygon = geoWriter.write(geometry);

var oLanLng = [];
var oCoordinates;
oCoordinates = polygon.coordinates[0];
for (i = 0; i < oCoordinates.length; i++) {
   var oItem;
   oItem = oCoordinates[i];
   oLanLng.push(new google.maps.LatLng(oItem[1], oItem[0]));
}

var polygone = new google.maps.Polygon({
    paths: oLanLng,
    map:map
});

How to draw a polygon around a polyline in JavaScript?

Solution 1:

Solution 2:

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