获取显示的OpenLayers地图的半径

Question

How do I compute the distance in mile/meters of the displayed Map? Assuming I have the coordinates of the center of the map. I would like to know the distance/radius from the center to the left/right most displayed part of the map? I already got this using Google Map but I'm new in Openlayers. Is there a way to achieve this? Right now my computation in GoogleMap is like this

var bounds = this.instance.getBounds();

var center = bounds.getCenter();
var ne = bounds.getNorthEast();

// r = radius of the earth in statute miles
var r = 3963.0;
var to_radians_divide = 57.2958;

// Convert lat or lng from decimal degrees into radians (divide by 57.2958)
var lat1 = center.lat() / to_radians_divide;
var lon1 = center.lng() / to_radians_divide;
var lat2 = ne.lat() / to_radians_divide;
var lon2 = ne.lng() / to_radians_divide;

// distance = circle radius from center to Northeast corner of bounds
var dis = r * Math.acos(Math.sin(lat1) * Math.sin(lat2) +
        Math.cos(lat1) * Math.cos(lat2) * Math.cos(lon2 - lon1));

return dis;

Is there a way to achieve this in OpenLayers? I just want to find out the distance of the left most part of the displayed map from the center

Answer 1

You can achieve this in openlayers also. Here is the code for that and I am using openlayers 3.20.0 version for this example.

    var size = map.getSize();
    var center = map.getView().getCenter();
    var sourceProj = map.getView().getProjection(); 
    var extent = map.getView().calculateExtent(size);

    extent = ol.proj.transformExtent(extent, sourceProj, 'EPSG:4326');
    var posSW = [extent[0], extent[1]];
    var posNE = [extent[2], extent[3]];
    center = ol.proj.transform(center, sourceProj, 'EPSG:4326'); 

    var wgs84Sphere = new ol.Sphere(6378137);
    var centerToSW = wgs84Sphere.haversineDistance(center, posSW);
    var centerToNE = wgs84Sphere.haversineDistance(center, posNE); 
    console.log("centerToSW - ",centerToSW);
    console.log("centerToNE - ",centerToNE);