如何在openlayers中绘制带有半径的圆

Question

我想在 openlayers 中画一个圆圈，半径以公里为单位。与特定地理点的中心？我遵循与http://demo.gwt-openlayers.org/gwt_ol_showcase/GwtOpenLayersShowcase.html?example=Draw%20Regular%20Polygon%20Example相同的方法，但我想使用预定义的值自动绘制。

Answer 1

以下代码将为您提供一个以当前地图为中心的浅蓝色圆圈，半径以米为单位。如果你想要以英尺为单位，只需更换：

        var radius = (radius / ol.proj.METERS_PER_UNIT.m) * resolutionFactor;

和：

        var radius = (radius / ol.proj.METERS_PER_UNIT.ft) * resolutionFactor;

代码：

   var drawCircleInMeter = function(map, radius) {
        var view = map.getView();
        var projection = view.getProjection();
        var resolutionAtEquator = view.getResolution();
        var center = map.getView().getCenter();
        var pointResolution = projection.getPointResolution(resolutionAtEquator, center);
        var resolutionFactor = resolutionAtEquator/pointResolution;
        var radius = (radius / ol.proj.METERS_PER_UNIT.m) * resolutionFactor;


        var circle = new ol.geom.Circle(center, radius);
        var circleFeature = new ol.Feature(circle);

        // Source and vector layer
        var vectorSource = new ol.source.Vector({
            projection: 'EPSG:4326'
        });
        vectorSource.addFeature(circleFeature);
        var vectorLayer = new ol.layer.Vector({
            source: vectorSource
        });

        map.addLayer(vectorLayer);
    }

注意。此处创建的 OpenLayers 圆始终是一个完美平坦的 2d 圆。而实际上，您可能想要更好地考虑地图投影的东西（尤其是靠近两极的地方）。