OpenLayers基础教程——WebGLPoints图层样式的设置方法-Toy模板网

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1、前言

前一篇博客介绍了如何在OpenLayers中使用WebGLPoints加载海量数据点的方法，这篇博客就来介绍一下WebGLPoints图层的样式设置问题。

2、样式运算符

在VectorLayer图层中，我们只需要创建一个ol.style.Style对象即可，WebGLPoints则不同，它并不是基于Canvas进行绘制，因此其样式渲染不能直接使用ol.style.Style，取而代之的是使用样式表达式进行渲染。

2.1、读取运算符

['get', 'attributeName']
['var', 'varName']
['time']
['zoom']
['resolution']

2.2、数学运算符

['*', value1, value2]
['/', value1, value2]
['+', value1, value2]
['-', value1, value2]
['clamp', value, low, high]
['%', value1, value2]
['^', value1, value2]

2.3、变换运算符

['case', condition1, output1, ...conditionN, outputN, fallback]
['match', input, match1, output1, ...matchN, outputN, fallback]
['interpolate', interpolation, input, stop1, output1, ...stopN, outputN]

2.4、逻辑运算符

['<', value1, value2]
['<=', value1, value2]
['>', value1, value2]
['>=', value1, value2]
['==', value1, value2]
['!=', value1, value2]
['!', value1]
['between', value1, value2, value3]

2.5、转换运算符

['array', value1, ...valueN]
['color', red, green, blue, alpha]

3、简单渲染

简单颜色渲染很简单，只需要使用['color', red, green, blue, alpha]即可，第一个参数为固定值‘color’，后面的参数依次为红、绿、蓝、透明度。下面的代码会将要素渲染为红色点：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL</title>
    <style>
        html,
        body,
        #map {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <link rel="stylesheet" href="ol/ol.css" />
    <script src="ol/ol.js"></script>
</head>
<body>
    <div id="map"></div>
    <script>
        // 创建图层
        var layer = new ol.layer.WebGLPoints({
            source: new ol.source.Vector({
                features: [
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.0]),
                        "type": "学校",
                        "dbm": 1
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.1]),
                        "type": "学校",
                        "dbm": 2
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.0]),
                        "type": "超市",
                        "dbm": 3
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.1]),
                        "type": "超市",
                        "dbm": 4
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.0]),
                        "type": "医院",
                        "dbm": 5
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.1]),
                        "type": "医院",
                        "dbm": 6
                    }),
                ]
            }),
            style: {
                symbol: {
                    symbolType: 'circle',
                    size: 40,
                    color: ['color', 255, 0, 0, 1]
                }
            }
        });

        // 创建地图
        var map = new ol.Map({
            target: 'map',
            layers: [
                layer
            ],
            view: new ol.View({
                projection: 'EPSG:4326',
                center: [120, 30],
                zoom: 10
            })
        });
    </script>
</body>
</html>

运行结果如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

4、分类渲染

测试数据中的type字段将要素分成了3类，即：学校、超市、医院。现在要求将学校渲染为红色、超市渲染为绿色、医院渲染为蓝色。此时需要使用match表达式，其形式如下所示：

['match', type的值, '学校', 红色, '超市', 绿色, '医院', 蓝色, 默认颜色]

那么type的值又该如何获取？其实很简单，使用['get', 'attributeName']表达式即可，所以最后的样式表达式如下所示：

['match', ['get', 'type'], '学校', 红色, '超市', 绿色, '医院', 蓝色, 默认颜色]

代码如下所示：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL</title>
    <style>
        html,
        body,
        #map {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <link rel="stylesheet" href="ol/ol.css" />
    <script src="ol/ol.js"></script>
</head>
<body>
    <div id="map"></div>
    <script>
        // 创建图层
        var layer = new ol.layer.WebGLPoints({
            source: new ol.source.Vector({
                features: [
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.0]),
                        "type": "学校",
                        "dbm": 1
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.1]),
                        "type": "学校",
                        "dbm": 2
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.0]),
                        "type": "超市",
                        "dbm": 3
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.1]),
                        "type": "超市",
                        "dbm": 4
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.0]),
                        "type": "医院",
                        "dbm": 5
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.1]),
                        "type": "医院",
                        "dbm": 6
                    }),
                ]
            }),
            style: {
                symbol: {
                    symbolType: 'circle',
                    size: 40,
                    color: [
                        'match',
                        ['get', 'type'], 
                        '学校', ['color', 255, 0, 0, 1],
                        '超市', ['color', 0, 255, 0, 1],
                        '医院', ['color', 0, 0, 255, 1],
                        ['color', 255, 0, 0, 1]
                    ]
                }
            }
        });

        // 创建地图
        var map = new ol.Map({
            target: 'map',
            layers: [
                layer
            ],
            view: new ol.View({
                projection: 'EPSG:4326',
                center: [120, 30],
                zoom: 10
            })
        });
    </script>
</body>
</html>

运行结果如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

5、分级渲染

测试数据中包含一个dbm字段，现在根据dbm的范围进行分级渲染，规定如下：
1、dbm∈[1, 2]，渲染为红色
2、dbm == 3，渲染为绿色
3、dbm == 4，渲染为蓝色
4、dbm∈[5, 6]，渲染为黄色

此时需要使用case表达式，其形式如下所示：

['case', 'dbm∈[1,2]', 红色, 'dbm==3', 绿色, 'dbm==4', 蓝色, 'dbm∈[5,6]', 红色， 默认颜色]

在判断dbm的值的范围时，需要使用逻辑表达式：

['==', dbm, 3]
['==', dbm, 4]
['between', dbm, 1, 2]
['between', dbm, 5, 6]

最后，使用['get', 'attributeName']表达式获取字段值：

['get', 'dbm']

代码如下所示：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL</title>
    <style>
        html,
        body,
        #map {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <link rel="stylesheet" href="ol/ol.css" />
    <script src="ol/ol.js"></script>
</head>
<body>
    <div id="map"></div>
    <script>
        // 创建图层
        var layer = new ol.layer.WebGLPoints({
            source: new ol.source.Vector({
                features: [
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.0]),
                        "type": "学校",
                        "dbm": 1
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.1]),
                        "type": "学校",
                        "dbm": 2
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.0]),
                        "type": "超市",
                        "dbm": 3
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.1]),
                        "type": "超市",
                        "dbm": 4
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.0]),
                        "type": "医院",
                        "dbm": 5
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.1]),
                        "type": "医院",
                        "dbm": 6
                    }),
                ]
            }),
            style: {
                symbol: {
                    symbolType: 'circle',
                    size: 40,
                    color: [
                        'case',
                        ['between', ['get', 'dbm'], 1, 2], ['color', 255, 0, 0, 1],
                        ['==', ['get', 'dbm'], 3], ['color', 0, 255, 0, 1],
                        ['==', ['get', 'dbm'], 4], ['color', 0, 0, 255, 1],
                        ['between', ['get', 'dbm'], 5, 6], ['color', 255, 255, 0, 1],
                        ['color', 255, 0, 0, 1]
                    ]
                }
            }
        });

        // 创建地图
        var map = new ol.Map({
            target: 'map',
            layers: [
                layer
            ],
            view: new ol.View({
                projection: 'EPSG:4326',
                center: [120, 30],
                zoom: 10
            })
        });
    </script>
</body>
</html>

运行结果如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

6、根据地图缩放等级渲染

现做如下规定：
1、地图缩放等级zoom∈（0, 10]，渲染为红色
2、地图缩放等级zoom∈（10, 12]，渲染为绿色
3、地图缩放等级zoom∈（12, 14]，渲染为蓝色
4、其余缩放等级，渲染为黄色

看了上面的例子之后，相信同志们应该想到了：利用['zoom']获取地图缩放等级，然后利用case表达式进行情况分类，最后每种情况利用逻辑表达式判断即可。代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL</title>
    <style>
        html,
        body,
        #map {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <link rel="stylesheet" href="ol/ol.css" />
    <script src="ol/ol.js"></script>
</head>
<body>
    <div id="map"></div>
    <script>
        // 创建图层
        var layer = new ol.layer.WebGLPoints({
            source: new ol.source.Vector({
                features: [
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.0]),
                        "type": "学校",
                        "dbm": 1
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.1]),
                        "type": "学校",
                        "dbm": 2
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.0]),
                        "type": "超市",
                        "dbm": 3
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.1]),
                        "type": "超市",
                        "dbm": 4
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.0]),
                        "type": "医院",
                        "dbm": 5
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.1]),
                        "type": "医院",
                        "dbm": 6
                    }),
                ]
            }),
            style: {
                symbol: {
                    symbolType: 'circle',
                    size: 40,
                    color: [
                        'case',
                        ['<=', ['zoom'], 10], ['color', 255, 0, 0, 1],
                        ['<=', ['zoom'], 12], ['color', 0, 255, 0, 1],
                        ['<=', ['zoom'], 14], ['color', 0, 0, 255, 1],
                        ['color', 255, 255, 0, 1]
                    ]
                }
            }
        });

        // 创建地图
        var map = new ol.Map({
            target: 'map',
            layers: [
                layer
            ],
            view: new ol.View({
                projection: 'EPSG:4326',
                center: [120, 30],
                zoom: 10
            })
        });
    </script>
</body>
</html>

运行结果如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

7、根据地图分辨率渲染

根据地图分辨率渲染也很简单，只需要把上面的['zoom']替换成['resolution']即可。不过考虑到resolution值是一个小数，因此这里将resolution乘以10000之后再进行判断，代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL</title>
    <style>
        html,
        body,
        #map {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <link rel="stylesheet" href="ol/ol.css" />
    <script src="ol/ol.js"></script>
</head>
<body>
    <div id="map"></div>
    <script>
        // 创建图层
        var layer = new ol.layer.WebGLPoints({
            source: new ol.source.Vector({
                features: [
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.0]),
                        "type": "学校",
                        "dbm": 1
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.1]),
                        "type": "学校",
                        "dbm": 2
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.0]),
                        "type": "超市",
                        "dbm": 3
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.1]),
                        "type": "超市",
                        "dbm": 4
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.0]),
                        "type": "医院",
                        "dbm": 5
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.1]),
                        "type": "医院",
                        "dbm": 6
                    }),
                ]
            }),
            style: {
                symbol: {
                    symbolType: 'circle',
                    size: 40,
                    color: [
                        'case',
                        ['<=', ['*', ['resolution'], 10000], 2], ['color', 255, 0, 0, 1],
                        ['<=', ['*', ['resolution'], 10000], 3], ['color', 0, 255, 0, 1],
                        ['<=', ['*', ['resolution'], 10000], 4], ['color', 0, 0, 255, 1],
                        ['<=', ['*', ['resolution'], 10000], 5], ['color', 255, 255, 0, 1],
                        ['<=', ['*', ['resolution'], 10000], 6], ['color', 255, 0, 255, 1],
                        ['<=', ['*', ['resolution'], 10000], 7], ['color', 0, 255, 255, 1],
                        ['color', 300, 200, 100, 1]
                    ]
                }
            }
        });

        // 创建地图
        var map = new ol.Map({
            target: 'map',
            layers: [
                layer
            ],
            view: new ol.View({
                projection: 'EPSG:4326',
                center: [120, 30],
                zoom: 10
            })
        });
    </script>
</body>
</html>

运行结果如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

8、设置要素的形状和透明度

在symbol对象中，symbolType参数用于定义要素的形状，它可以设置为circle、triangle、square、image。例如将symbolType设置为triangle：

symbol: {
    symbolType: 'circle',
    size: 40,
    color: ['color', 255, 0, 0, 1]
}

此时要素会被渲染为三角形，如下图所示：

['var', 'varname'] ol,JavaScript,openlayers
将symbolType设置为square：

symbol: {
    symbolType: 'square',
    size: 40,
    color: ['color', 255, 0, 0, 1]
}

此时要素会被渲染为正方形，如下图所示：

['var', 'varname'] ol,JavaScript,openlayers
如果希望设置透明度，只需要添加opacity属性即可，例如将透明度设置为0.3：

symbol: {
    symbolType: 'circle',
    size: 40,
    color: ['color', 255, 0, 0, 1],
    opacity: 0.3
}

如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

9、设置要素的尺寸

上面的代码主要针对color属性进行设置，其实不仅仅是color，size属性同样可以使用样式表达式。现在根据dbm值生成不同大小的要素，代码如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL</title>
    <style>
        html,
        body,
        #map {
            width: 100%;
            height: 100%;
            margin: 0;
            padding: 0;
        }
    </style>
    <link rel="stylesheet" href="ol/ol.css" />
    <script src="ol/ol.js"></script>
</head>
<body>
    <div id="map"></div>
    <script>
        // 创建图层
        var layer = new ol.layer.WebGLPoints({
            source: new ol.source.Vector({
                features: [
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.0]),
                        "type": "学校",
                        "dbm": 1
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.0, 30.1]),
                        "type": "学校",
                        "dbm": 2
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.0]),
                        "type": "超市",
                        "dbm": 3
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.1, 30.1]),
                        "type": "超市",
                        "dbm": 4
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.0]),
                        "type": "医院",
                        "dbm": 5
                    }),
                    new ol.Feature({
                        geometry: new ol.geom.Point([120.2, 30.1]),
                        "type": "医院",
                        "dbm": 6
                    }),
                ]
            }),
            style: {
                symbol: {
                    symbolType: 'circle',
                    size: [
                        'case',
                        ['==', ['get', 'dbm'], 1], 10,
                        ['==', ['get', 'dbm'], 2], 20,
                        ['==', ['get', 'dbm'], 3], 30,
                        ['==', ['get', 'dbm'], 4], 40,
                        ['==', ['get', 'dbm'], 5], 50,
                        ['==', ['get', 'dbm'], 6], 60,
                        20
                    ],
                    color: ['color', 255, 0, 0, 1],
                }
            }
        });

        // 创建地图
        var map = new ol.Map({
            target: 'map',
            layers: [
                layer
            ],
            view: new ol.View({
                projection: 'EPSG:4326',
                center: [120, 30],
                zoom: 10
            })
        });
    </script>
</body>
</html>

运行结果如下图所示：

['var', 'varname'] ol,JavaScript,openlayers

10、结语

本文主要介绍了OpenLayers中WebGLPoints图层的样式设置方法。其实刚接触样式表达式的时候觉得这种方法很反人类，但是习惯之后发现它的灵活度很高，本文也只列举了一些常见的用法，有兴趣的同志可以去官网查看更详细的文档。文章来源地址https://www.toymoban.com/news/detail-859571.html

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