How to display curved polyline on one side of a straight line?

Question

This question is related to this SO question and answered by @geocodezip.

A problem I have is drawing a line from either north-to-south or south-to-north. The curved

Answer 1

A general routine to draw the Bezier curve you are looking for would be:

function drawDashedCurve(P1, P2, map) {
  var lineLength = google.maps.geometry.spherical.computeDistanceBetween(P1, P2);
  var lineHeading = google.maps.geometry.spherical.computeHeading(P1, P2);
  if (lineHeading < 0) {
    var lineHeading1 = lineHeading + 45;
    var lineHeading2 = lineHeading + 135;
  } else {
    var lineHeading1 = lineHeading + -45;
    var lineHeading2 = lineHeading + -135;
  }
  var pA = google.maps.geometry.spherical.computeOffset(P1, lineLength / 2.2, lineHeading1);
  var pB = google.maps.geometry.spherical.computeOffset(P2, lineLength / 2.2, lineHeading2);

  var curvedLine = new GmapsCubicBezier(P1, pA, pB, P2, 0.01, map);
}

Changing the angles and distance to compute the control points (pA, pB) will change the amount of curvature.

test fiddle

code snippet:

// draw a dashed curve anchored at P1, P2
function drawDashedCurve(P1, P2, map) {
  var lineLength = google.maps.geometry.spherical.computeDistanceBetween(P1, P2);
  var lineHeading = google.maps.geometry.spherical.computeHeading(P1, P2);
  if (lineHeading < 0) {
    var lineHeading1 = lineHeading + 45;
    var lineHeading2 = lineHeading + 135;
  } else {
    var lineHeading1 = lineHeading + -45;
    var lineHeading2 = lineHeading + -135;
  }
  var pA = google.maps.geometry.spherical.computeOffset(P1, lineLength / 2.2, lineHeading1);
  var pB = google.maps.geometry.spherical.computeOffset(P2, lineLength / 2.2, lineHeading2);

  var curvedLine = new GmapsCubicBezier(P1, pA, pB, P2, 0.01, map);
}

function initialize() {
  var map = new google.maps.Map(
    document.getElementById("map_canvas"), {
      center: new google.maps.LatLng(37.4419, -122.1419),
      zoom: 13,
      mapTypeId: google.maps.MapTypeId.ROADMAP
    });
  // generate test points every 10 degrees
  for (var angle = 0; angle < 360; angle += 10) {
    var p1 = google.maps.geometry.spherical.computeOffset(map.getCenter(), 1000, angle);
    var p2 = google.maps.geometry.spherical.computeOffset(map.getCenter(), 2000, angle);
    drawDashedCurve(p1, p2, map);
    var straightPoly = new google.maps.Polyline({
      map: map,
      path: [p1, p2],
      strokeOpacity: 0.2,
      strokeColor: "blue"
    });
    var markerP1 = new google.maps.Marker({
      position: p1,
      map: map,
      icon: {
        path: google.maps.SymbolPath.CIRCLE,
        scale: 4,
        fillColor: "black",
        fillOpacity: 1.0
      }
    });
    var markerP2 = new google.maps.Marker({
      position: p2,
      map: map,
      icon: {
        path: google.maps.SymbolPath.CIRCLE,
        scale: 4,
        fillColor: "black",
        fillOpacity: 1.0
      }
    });
  }
}
google.maps.event.addDomListener(window, "load", initialize);

// original Belzier Curve code from nicoabie's answer to this question on StackOverflow:
// http://stackoverflow.com/questions/5347984/letting-users-draw-curved-lines-on-a-google-map
var GmapsCubicBezier = function(latlong1, latlong2, latlong3, latlong4, resolution, map) {
  var lat1 = latlong1.lat();
  var long1 = latlong1.lng();
  var lat2 = latlong2.lat();
  var long2 = latlong2.lng();
  var lat3 = latlong3.lat();
  var long3 = latlong3.lng();
  var lat4 = latlong4.lat();
  var long4 = latlong4.lng();

  var points = [];

  for (it = 0; it <= 1; it += resolution) {
    points.push(this.getBezier({
      x: lat1,
      y: long1
    }, {
      x: lat2,
      y: long2
    }, {
      x: lat3,
      y: long3
    }, {
      x: lat4,
      y: long4
    }, it));
  }
  var path = [];
  for (var i = 0; i < points.length - 1; i++) {
    path.push(new google.maps.LatLng(points[i].x, points[i].y));
    path.push(new google.maps.LatLng(points[i + 1].x, points[i + 1].y, false));
  }

  var Line = new google.maps.Polyline({
    path: path,
    geodesic: true,
    strokeOpacity: 0.0,
    icons: [{
      icon: {
        path: 'M 0,-1 0,1',
        strokeOpacity: 1,
        scale: 4
      },
      offset: '0',
      repeat: '20px'
    }],
    strokeColor: 'grey'
  });

  Line.setMap(map);

  return Line;
};


GmapsCubicBezier.prototype = {

  B1: function(t) {
    return t * t * t;
  },
  B2: function(t) {
    return 3 * t * t * (1 - t);
  },
  B3: function(t) {
    return 3 * t * (1 - t) * (1 - t);
  },
  B4: function(t) {
    return (1 - t) * (1 - t) * (1 - t);
  },
  getBezier: function(C1, C2, C3, C4, percent) {
    var pos = {};
    pos.x = C1.x * this.B1(percent) + C2.x * this.B2(percent) + C3.x * this.B3(percent) + C4.x * this.B4(percent);
    pos.y = C1.y * this.B1(percent) + C2.y * this.B2(percent) + C3.y * this.B3(percent) + C4.y * this.B4(percent);
    return pos;
  }
};

html,
body,
#map_canvas {
  height: 100%;
  width: 100%;
  margin: 0px;
  padding: 0px
}

<script src="https://maps.googleapis.com/maps/api/js?libraries=geometry&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<div id="map_canvas"></div>