1. draw = new ol.interaction.Draw({
    2.                 // 在哪个画布上绘制
    3.                 source: source,
    4.                 // 绘制的类型
    5.                 type: 'LineString',
    6.                 geometryFunction: function (coordinates, geometry) {
    7.                     if (!geometry) {
    8.                         //多边形
    9.                         geometry = new ol.geom.Polygon(null)
    10.                     }
    11.                     var start = coordinates[0]
    12.                     var end = coordinates[1]
    13.                     geometry.setCoordinates([
    14.                         [start, [start[0], end[1]], end, [end[0], start[1]], start],
    15.                     ])
    16.                     return geometry
    17.                 },
    18.                 maxPoints: 2
    19. })

    image.png

    逆时针