使用pgrouting进行最短路径搜索

   PgRouting是基于开源空间数据库PostGIS用于网络分析的扩展模块，最初它被称作pgDijkstra，因为它只是利用Dijkstra算法实现最短路径搜索，之后慢慢添加了其他的路径分析算法，如A算法，双向A算法，Dijkstra算法，双向Dijkstra算法，tsp货郎担算法等，然后被更名为pgRouting。该扩展库依托PostGIS自身的gist索引，丰富的坐标系与图形类型，强大的几何处理能力，如空间查询，空间处理，线性参考等优势，能保障在较大数据级别下的网络分析效果更快更好。

最新源码见：

https://github.com/wilsonfu88/MapRoutingDemo

1、环境搭建

需要先安装PostgreSQL9.6，再安装PostGIS，注意版本号PostGIS2.4后已经集成了pgRouting，无需单独安装

PostGIS 官网 http://www.postgis.org/

pgRouting官网http://pgrouting.org/documentation.html

2、启用pgRouting功能，连接到对应postgres数据库后执行下面的sql语句

CREATE EXTENSION postgis;
CREATE EXTENSION pgrouting;

3、路网数据处理

由于路网分析的特殊性，只支持LineString类型，不支持MultiLineString类型，如果路网数据为MultiLineString类型导入前需加工处理，可使用arcgis在交叉点处使用打断相交线来分割线，参见

http://resources.arcgis.com/zh-cn/help/main/10.1/index.html#//01m8，最终可用的数据必须为路网不自相交，导入时选择简单的线类型，否则网络拓扑计算数据会错误

 

4、路网拓扑数据计算处理，执行成功后，执行成功后会生产一个**_vertices_pgr的表，里面包含路网相交点的空间数据

 alter table road add column source int;

alter table road add column target int;

create index road_source_idx on road("source");
create index road_target_idx on road("target");

ALTER TABLE road  ADD COLUMN length double precision;  

SELECT pgr_createTopology('road',0.00001, 'geom', 'gid');  

update road set length =st_length(geom); 

5、查询最短路径sql语句

SELECT seq, id1 AS node, id2 AS edge, cost,geom  FROM pgr_dijkstra('
SELECT gid AS id,
source::integer,
target::integer,
length::double precision AS cost
FROM xmpark_road',
1, 10, false, false) as di
join xmpark_road pt
on di.id2 = pt.gid

6、参数化的查询sql语句，可以用下面的语句，在geoserver中使用发布sql视图图层来显示导航搜索图层，见下图

SELECT seq, id1 AS node, id2 AS edge, cost,geom  FROM pgr_dijkstra('
SELECT gid AS id,
source::integer,
target::integer,
length::double precision AS cost
FROM xmpark_road',
%a%, %b%, false, false) as di
join xmpark_road pt
on di.id2 = pt.gid

 7、在ol中使用上面发布的搜索图层使用起止交叉点来显示导航路径，源码如下

 <!DOCTYPE html>
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
     <title></title>
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width,initial-scale=1.0,user-scalable=no" />
     <link rel="stylesheet" href="ol/ol.css" type="text/css">
     <script src="ol/ol-debug.js"></script>
     <script src="ol/proj4.js"></script>
     <script src="js/jquery-1.8.0.min.js"></script>
     <meta charset="utf-8" />
 </head>
 <body>
     <div id="map" style="width: 100%;height:800px;border:solid 1px red" class="map">
         <div>
             id1: <input id="id1" value="30" />
             id2: <input id="id2" value="66" />
             <input type="button" value="query" onclick="queryRoute()" />
         </div>
     </div>
 </body>
 </html>

 <script type="text/javascript">
     var format = 'image/png';
     var bounds = [501369.9375, 2494100.25,
         502073, 2495256.25];
     var mousePositionControl = new ol.control.MousePosition({
         className: 'custom-mouse-position',
         target: document.getElementById('location'),
         coordinateFormat: ol.coordinate.createStringXY(5),
         undefinedHTML: '&nbsp;'
     });
     var tiled = new ol.layer.Tile({
         visible: true,
         source: new ol.source.TileWMS({
             url: 'http://localhost:8080/geoserver/pg_ws/wms',
             params: {
                 'FORMAT': format,
                 'VERSION': '1.1.1',
                 tiled: true,
                 STYLES: '',
                 LAYERS: 'pg_ws:xmpark_road',
             }
         })
     });

     var cross_tiled = new ol.layer.Tile({
         //visible: true,
         source: new ol.source.TileWMS({
             url: 'http://localhost:8080/geoserver/pg_ws/wms',
             params: {
                 'FORMAT': format,
                 'VERSION': '1.1.1',
                 tiled: true,
                 STYLES: '',
                 LAYERS: 'pg_ws:xmpark_road_vertices_pgr',
             }
         })
     });

     var projection = new ol.proj.Projection({
         code: 'EPSG:3857',
         units: 'm',
         axisOrientation: 'neu',
         global: true
     });
     var map = new ol.Map({
         controls: ol.control.defaults({
             attribution: false
         }).extend([mousePositionControl]),
         target: 'map',
         layers: [
             tiled, cross_tiled
         ],
         view: new ol.View({
             projection: projection
         })
     });

     map.getView().fit(bounds, map.getSize());

     var routeLayer = null;

     function queryRoute() {
         if (routeLayer != null) {
             map.removeLayer(routeLayer);
         }

         var val1 = $("#id1").val();
         var val2 = $("#id2").val();
          routeLayer = new ol.layer.Tile({
             visible: true,
             source: new ol.source.TileWMS({
                 url: 'http://localhost:8080/geoserver/pg_ws/wms',
                 params: {
                     'FORMAT': format,
                     'VERSION': '1.1.1',
                     tiled: true,
                     STYLES: '',
                     LAYERS: 'pg_ws:xmpark_road_route',
                     'viewparams': 'a:' + val1 + ';b:' + val2
                 }
             })
         });

         map.addLayer(routeLayer);
     }
 </script>

导航图层搜索

最终实现效果如下：