openlayers线的折点处加箭头

通过使用OpenLayers的Style对象，您可以轻松地在折点处添加箭头样式。您可以使用arrow图片或SVG，也可以通过旋转线段并在末端添加箭头来创建箭头效果。以下是示例代码：

var style = new ol.style.Style({
    stroke: new ol.style.Stroke({
        color: 'blue',
        width: 2,
        lineDash: [4],
        lineCap: 'round',
        lineJoin: 'round'
    })
});
style.setGeometry(function(feature) {
    // get the geometry of the feature
    var geometry = feature.getGeometry();
    var coordinates = geometry.getCoordinates();
    
    // create an arrow head at the end of the line
    var last = coordinates[coordinates.length - 2];
    var nextToLast = coordinates[coordinates.length - 3];
    var dx = last[0] - nextToLast[0];
    var dy = last[1] - nextToLast[1];
    var rotation = Math.atan2(dy, dx);
    var arrowCoords = [
        [last[0], last[1]],
        [last[0] - 15 * Math.cos(rotation - Math.PI / 7), last[1] - 15 * Math.sin(rotation - Math.PI / 7)],
        [last[0] - 15 * Math.cos(rotation + Math.PI / 7), last[1] - 15 * Math.sin(rotation + Math.PI / 7)]
    ];
    coordinates[coordinates.length - 1] = arrowCoords[0];
    coordinates.push(arrowCoords[1], arrowCoords[2], arrowCoords[0]);
    
    // create the line geometry with arrow head
    var line = new ol.geom.LineString(coordinates);
    return line;
});

这将在折点处添加一个箭头样式，该箭头样式针对特定的要素。您可以使用feature.setGeometry方法将该样式应用于要素，或者使用其他OpenLayers方法（如矢量层或矢量图层源）来添加您的要素。