在openlayers3中不使用任何图像绘制箭头

Question

如何在 Openlayers 3 地图中的矢量图层上绘制箭头？ 我尝试使用 canvaselement 创建一个箭头，但不知道如何在 ol3 地图上绘制它。

Answer 1

画布元素不是必需的。您可以从Openlayers site 中获取箭头示例，并添加 2 个自定义 LineString 元素而不是图标。您已经在示例中了解了以弧度为单位的旋转角度以及应该添加代码的事件。

希望下面的 sn-p 可以解决问题：

var source = new ol.source.Vector();

var styleFunction = function (feature) {
    var geometry = feature.getGeometry();
    var styles = [
        // linestring
        new ol.style.Style({
            stroke: new ol.style.Stroke({
                color: '#ffcc33',
                width: 2
            })
        })
    ];

    geometry.forEachSegment(function (start, end) {
        var dx = end[0] - start[0];
        var dy = end[1] - start[1];
        var rotation = Math.atan2(dy, dx);

        var lineStr1 = new ol.geom.LineString([end, [end[0] - 200000, end[1] + 200000]]);
        lineStr1.rotate(rotation, end);
        var lineStr2 = new ol.geom.LineString([end, [end[0] - 200000, end[1] - 200000]]);
        lineStr2.rotate(rotation, end);

        var stroke = new ol.style.Stroke({
            color: 'green',
            width: 1
        });

        styles.push(new ol.style.Style({
            geometry: lineStr1,
            stroke: stroke
        }));
        styles.push(new ol.style.Style({
            geometry: lineStr2,
            stroke: stroke
        }));
    });

    return styles;
};

var map = new ol.Map({
    layers: [
        new ol.layer.Tile({
            source: new ol.source.OSM()
        }),
        new ol.layer.Vector({
            source: source,
            style: styleFunction
        })
    ],
    target: 'map',
    view: new ol.View({
        center: [0, 0],
        zoom: 3
    })
});

map.addInteraction(new ol.interaction.Draw({
    source: source,
    type: ('LineString')
}));

<script src="https://openlayers.org/en/v3.20.1/build/ol.js"></script>
<link href="https://openlayers.org/en/v3.20.1/css/ol.css" rel="stylesheet"/>
<div id="map" class="map" tabindex="0"></div>

Answer 2

这是Openlayers line-arrow Example 的另一个自定义。 它使用RegularShape 而不是图像。箭头将保持其大小独立于当前地图缩放。

var source = new ol.source.Vector();

var styleFunction = function (feature) {
    var geometry = feature.getGeometry();
    var styles = [
        // linestring
        new ol.style.Style({
            stroke: new ol.style.Stroke({
                color: '#000',
                width: 2
            })
        })
    ];

    geometry.forEachSegment(function (start, end) {
        var dx = end[0] - start[0];
        var dy = end[1] - start[1];
        var rotation = Math.atan2(dy, dx);

        styles.push(new ol.style.Style({
          geometry: new ol.geom.Point(end),
          image: new ol.style.RegularShape({
            fill: new ol.style.Fill({color: '#000'}),
            points: 3,
            radius: 8,
            rotation: -rotation,
            angle: Math.PI / 2 // rotate 90°
          })
        }));
    });

    return styles;
};

var map = new ol.Map({
    layers: [
        new ol.layer.Tile({
            source: new ol.source.OSM()
        }),
        new ol.layer.Vector({
            source: source,
            style: styleFunction
        })
    ],
    target: 'map',
    view: new ol.View({
        center: [0, 0],
        zoom: 3
    })
});

map.addInteraction(new ol.interaction.Draw({
    source: source,
    type: ('LineString')
}));

<script src="https://openlayers.org/en/v3.20.1/build/ol.js"></script>
<link href="https://openlayers.org/en/v3.20.1/css/ol.css" rel="stylesheet"/>
<div id="map" class="map" tabindex="0"></div>