Google Maps API 3：以像素为单位计算多边形的长度

Question

我在地图中有 2 个 (lat,lng) 标记：p1 和 p2。我需要以 pixels 为单位计算从 p1 到 p2 的多边形的长度。

这是我目前通过获取斜边值的解决方案：

//set global variables
var pixel_coordinates = [];
var overlay;

//create map
map = new google.maps.Map(document.getElementById('map'),myOptions);

//create overlay using this solution http://stackoverflow.com/questions/1538681/how-to-call-fromlatlngtodivpixel-in-google-maps-api-v3
function MyOverlay(options) {
    this.setValues(options);
    var div = this.div_= document.createElement('div');
    div.className = "overlay";
};
MyOverlay.prototype = new google.maps.OverlayView;
MyOverlay.prototype.onAdd = function() {
var pane = this.getPanes().overlayLayer;
    pane.appendChild(this.div_);
}
MyOverlay.prototype.onRemove = function() {
    this.div_.parentNode.removeChild(this.div_);
}
MyOverlay.prototype.draw = function() {
    var projection = this.getProjection();
    var position = projection.fromLatLngToDivPixel(this.getMap().getCenter());
    var div = this.div_;
    div.style.left = position.x + 'px';
    div.style.top = position.y + 'px';
    div.style.display = 'block';
};
overlay = new MyOverlay( { map: map } );

//fill x,y coordinates (from lat/lng points)
pixel_coordinates[0] = overlay.getProjection().fromLatLngToContainerPixel(p1);
pixel_coordinates[1] = overlay.getProjection().fromLatLngToContainerPixel(p2);

//calculate hypotenuse
var distance = Math.round(
    Math.sqrt(
        Math.pow(Math.abs(pixel_coordinates[0].x - pixel_coordinates[1].x),2)
        +
        Math.pow(Math.abs(pixel_coordinates[0].y - pixel_coordinates[1].y),2)
    )
);
console.log(pixel_coordinates[0].x + ', ' + pixel_coordinates[0].y);
console.log(pixel_coordinates[1].x + ', ' + pixel_coordinates[1].y);
console.log(distance);

问题在于 pixel_coordinates 接收的像素坐标与地图中的原始 p1 和 p2 点不匹配。有人能发现错误吗？

更新：它已经工作了，只要确保在计算像素坐标之前使用 map.fitBounds(viewport) :)

Answer 1

上面的代码有效，只是避免在获取fromLatLngToContainerPixel数据后使用fitBounds。

Answer 2

每条折线都有腿，每条腿都有台阶。每个 Steps 都包含 start lat_lng 和 end lat_lng。计算这两点之间的距离可以为您提供准确的像素距离。

function getPixelDistance( polyline ){
    var legs = polyline.legs;
    var steps;
    var distance = 0;
    for( var k = 0; k < legs.length; k++){
       steps = legs[k].steps;
       for( var i = 0; i < steps.length; i++ ){     

           distance += getDistance( steps[i].start_location, steps[i].end_location );
       }
    }    
     return distance;    
}     

    function getDistance( p1, 2 ){
      var pixel_coordinates = [];  
      overlay = new MyOverlay( { map: map } );
      pixel_coordinates[0] = overlay.getProjection().fromLatLngToContainerPixel(p1);
      pixel_coordinates[1] = overlay.getProjection().fromLatLngToContainerPixel(p2);
      var distance = Math.round(
          Math.sqrt(
             Math.pow(Math.abs(pixel_coordinates[0].x - pixel_coordinates[1].x),2)
             +
             Math.pow(Math.abs(pixel_coordinates[0].y - pixel_coordinates[1].y),2)
            )
        );
      return distance;
    }