geojson.js

用来在地图上做操作GIS,在地图上做标记

                }
                lines.push(l);
            }
            return new OpenLayers.Geometry.MultiLineString(lines);
        },
        
        /**
         * Method: parseCoords.polygon
         * Convert a coordinate array from GeoJSON into an
         *     <OpenLayers.Geometry>.
         *
         * Returns:
         * {<OpenLayers.Geometry>} A geometry.
         */
        "polygon": function(array) {
            var rings = [];
            var r, l;
            for(var i=0; i<array.length; ++i) {
                try {
                    l = this.parseCoords["linestring"].apply(this, [array[i]]);
                } catch(err) {
                    throw err;
                }
                r = new OpenLayers.Geometry.LinearRing(l.components);
                rings.push(r);
            }
            return new OpenLayers.Geometry.Polygon(rings);
        },

        /**
         * Method: parseCoords.multipolygon
         * Convert a coordinate array from GeoJSON into an
         *     <OpenLayers.Geometry>.
         *
         * Parameters:
         * array - {Object} The coordinates array from the GeoJSON fragment.
         *
         * Returns:
         * {<OpenLayers.Geometry>} A geometry.
         */
        "multipolygon": function(array) {
            var polys = [];
            var p = null;
            for(var i=0; i<array.length; ++i) {
                try {
                    p = this.parseCoords["polygon"].apply(this, [array[i]]);
                } catch(err) {
                    throw err;
                }
                polys.push(p);
            }
            return new OpenLayers.Geometry.MultiPolygon(polys);
        },

        /**
         * Method: parseCoords.box
         * Convert a coordinate array from GeoJSON into an
         *     <OpenLayers.Geometry>.
         *
         * Parameters:
         * array - {Object} The coordinates array from the GeoJSON fragment.
         *
         * Returns:
         * {<OpenLayers.Geometry>} A geometry.
         */
        "box": function(array) {
            if(array.length != 2) {
                throw "GeoJSON box coordinates must have 2 elements";
            }
            return new OpenLayers.Geometry.Polygon([
                new OpenLayers.Geometry.LinearRing([
                    new OpenLayers.Geometry.Point(array[0][0], array[0][1]),
                    new OpenLayers.Geometry.Point(array[1][0], array[0][1]),
                    new OpenLayers.Geometry.Point(array[1][0], array[1][1]),
                    new OpenLayers.Geometry.Point(array[0][0], array[1][1]),
                    new OpenLayers.Geometry.Point(array[0][0], array[0][1])
                ])
            ]);
        }

    },

    /**
     * APIMethod: write
     * Serialize a feature, geometry, array of features, or array of geometries
     *     into a GeoJSON string.
     *
     * Parameters:
     * obj - {Object} An <OpenLayers.Feature.Vector>, <OpenLayers.Geometry>,
     *     or an array of either features or geometries.
     * pretty - {Boolean} Structure the output with newlines and indentation.
     *     Default is false.
     *
     * Returns:
     * {String} The GeoJSON string representation of the input geometry,
     *     features, array of geometries, or array of features.
     */
    write: function(obj, pretty) {
        var geojson = {
            "type": null
        };
        if(obj instanceof Array) {
            if(obj[0] instanceof OpenLayers.Feature.Vector) {
                geojson.features = [];
            } else if (obj[0].CLASS_NAME.search("OpenLayers.Geometry") == 0) {
                geojson.geometries = [];
            }    
            for(var i=0; i<obj.length; ++i) {
                var element = obj[i];
                if(element instanceof OpenLayers.Feature.Vector) {
                    if(geojson.type == null) {
                        geojson.type = "FeatureCollection";
                        if(element.layer && element.layer.projection) {
                            geojson.crs = this.createCRSObject(element);
                        }
                    } else if(geojson.type != "FeatureCollection") {
                        OpenLayers.Console.error("FeatureCollection only supports collections of features: " + element);
                        break;
                    }
                    geojson.features.push(this.extract.feature.apply(this, [element]));
                } else if (element.CLASS_NAME.search("OpenLayers.Geometry") == 0) {
                    if(geojson.type == null) {
                        geojson.type = "GeometryCollection";
                    } else if(geojson.type != "GeometryCollection") {
                        OpenLayers.Console.error("GeometryCollection only supports collections of geometries: " + element);
                        break;
                    }
                    geojson.geometries.push(this.extract.geometry.apply(this, [element]));
                }
            }
        } else if (obj.CLASS_NAME.search("OpenLayers.Geometry") == 0) {
            geojson = this.extract.geometry.apply(this, [obj]);
        } else if (obj instanceof OpenLayers.Feature.Vector) {
            geojson = this.extract.feature.apply(this, [obj]);
            if(obj.layer && obj.layer.projection) {
                geojson.crs = this.createCRSObject(obj);
            }
        }
        return OpenLayers.Format.JSON.prototype.write.apply(this,
                                                            [geojson, pretty]);
    },

    /**
     * Method: createCRSObject
     * Create the CRS object for an object.
     *
     * Parameters:
     * object - {<OpenLayers.Feature.Vector>} 
     *
     * Returns:
     * {Object} An object which can be assigned to the crs property
     * of a GeoJSON object.
     */
    createCRSObject: function(object) {
       var proj = object.layer.projection;
       var crs = {}
       if (proj.match(/epsg:/i)) {
           var code = parseInt(proj.substring(proj.indexOf(":") + 1));
           if (code == 4326) {
               crs = {
                   "type": "OGC",
                   "properties": {
                       "urn": "urn:ogc:def:crs:OGC:1.3:CRS84"
                   }
               };
           } else {    
               crs = {
                   "type": "EPSG",
                   "properties": {
                       "code": code 
                   }
               };
           }    
       }
       return crs;
    },
    
    /**
     * Property: extract
     * Object with properties corresponding to the GeoJSON types.
     *     Property values are functions that do the actual value extraction.
     */
    extract: {
        /**
         * Method: extract.feature
         * Return a partial GeoJSON object representing a single feature.
         *
         * Parameters:
         * feature - {<OpenLayers.Feature.Vector>}
         *
         * Returns:
         * {Object} An object representing the point.
         */
        'feature': function(feature) {
            var geom = this.extract.geometry.apply(this, [feature.geometry]);
            return {
                "type": "Feature",
                "id": feature.fid == null ? feature.id : feature.fid,
                "properties": feature.attributes,
                "geometry": geom
            }
        },
        
        /**
         * Method: extract.geometry
         * Return a GeoJSON object representing a single geometry.
         *
         * Parameters:
         * geometry - {<OpenLayers.Geometry>}
         *
         * Returns:
         * {Object} An object representing the geometry.
         */
        'geometry': function(geometry) {
            var geometryType = geometry.CLASS_NAME.split('.')[2];
            var data = this.extract[geometryType.toLowerCase()].apply(this, [geometry]);
            return {
                "type": geometryType,
                "coordinates": data
            }
        },

        /**
         * Method: extract.poin
         * Return an array of coordinates from a point.
         *
         * Parameters:
         * point - {<OpenLayers.Geometry.Point>}
         *
         * Returns: 
         * {Array} An array of coordinates representing the point.
         */
        'point': function(point) {
            return [point.x, point.y];
        },

        /**
         * Method: extract.multipoint
         * Return an array of point coordinates from a multipoint.
         *
         * Parameters:
         * multipoint - {<OpenLayers.Geometry.MultiPoint>}
         *
         * Returns:
         * {Array} An array of point coordinate arrays representing
         *     the multipoint.
         */
        'multipoint': function(multipoint) {
            var array = [];
            for(var i=0; i<multipoint.components.length; ++i) {
                array.push(this.extract.point.apply(this, [multipoint.components[i]]));
            }
            return array;
        },
        
        /**
         * Method: extract.linestring
         * Return an array of coordinate arrays from a linestring.
         *
         * Parameters:
         * linestring - {<OpenLayers.Geometry.LineString>}
         *
         * Returns:
         * {Array} An array of coordinate arrays representing
         *     the linestring.
         */
        'linestring': function(linestring) {
            var array = [];
            for(var i=0; i<linestring.components.length; ++i) {
                array.push(this.extract.point.apply(this, [linestring.components[i]]));
            }
            return array;
        },

        /**
         * Method: extract.multilinestring
         * Return an array of linestring arrays from a linestring.
         * 
         * Parameters:
         * linestring - {<OpenLayers.Geometry.MultiLineString>}
         * 
         * Returns:
         * {Array} An array of linestring arrays representing
         *     the multilinestring.
         */
        'multilinestring': function(multilinestring) {
            var array = [];
            for(var i=0; i<multilinestring.components.length; ++i) {
                array.push(this.extract.linestring.apply(this, [multilinestring.components[i]]));
            }
            return array;
        },
        
        /**
         * Method: extract.polygon
         * Return an array of linear ring arrays from a polygon.
         *
         * Parameters:
         * polygon - {<OpenLayers.Geometry.Polygon>}
         * 
         * Returns:
         * {Array} An array of linear ring arrays representing the polygon.
         */
        'polygon': function(polygon) {
            var array = [];
            for(var i=0; i<polygon.components.length; ++i) {
                array.push(this.extract.linestring.apply(this, [polygon.components[i]]));
            }
            return array;
        },

        /**
         * Method: extract.multipolygon
         * Return an array of polygon arrays from a multipolygon.
         * 
         * Parameters:
         * multipolygon - {<OpenLayers.Geometry.MultiPolygon>}
         * 
         * Returns:
         * {Array} An array of polygon arrays representing
         *     the multipolygon
         */
        'multipolygon': function(multipolygon) {
            var array = [];
            for(var i=0; i<multipolygon.components.length; ++i) {
                array.push(this.extract.polygon.apply(this, [multipolygon.components[i]]));
            }
            return array;
        }

    },

    CLASS_NAME: "OpenLayers.Format.GeoJSON" 

});