layer.js

用来在地图上做操作GIS,在地图上做标记

/* Copyright (c) 2006-2007 MetaCarta, Inc., published under the BSD license.
 * See http://svn.openlayers.org/trunk/openlayers/release-license.txt 
 * for the full text of the license. */


/**
 * @requires OpenLayers/Map.js
 * 
 * Class: OpenLayers.Layer
 */
OpenLayers.Layer = OpenLayers.Class({

    /**
     * APIProperty: id
     * {String}
     */
    id: null,

    /** 
     * APIProperty: name
     * {String}
     */
    name: null,

    /** 
     * APIProperty: div
     * {DOMElement}
     */
    div: null,

    /** 
     * Constant: EVENT_TYPES
     * {Array(String)} Supported application event types
     */
    EVENT_TYPES: [ "loadstart", "loadend", "loadcancel", "visibilitychanged"],
        
    /**
     * APIProperty: events``
     * {<OpenLayers.Events>}
     */
    events: null,

    /**
     * APIProperty: map
     * {<OpenLayers.Map>} This variable is set when the layer is added to 
     *     the map, via the accessor function setMap().
     */
    map: null,
    
    /**
     * APIProperty: isBaseLayer
     * {Boolean} Whether or not the layer is a base layer. This should be set 
     *     individually by all subclasses. Default is false
     */
    isBaseLayer: false,
 
    /**
     * Property: alpha
     * {Boolean} The layer's images have an alpha channel.  Default is false. 
     */
    alpha: false,

    /** 
     * APIProperty: displayInLayerSwitcher
     * {Boolean} Display the layer's name in the layer switcher.  Default is
     *     true.
     */
    displayInLayerSwitcher: true,

    /**
     * APIProperty: visibility
     * {Boolean} The layer should be displayed in the map.  Default is true.
     */
    visibility: true,

    /**
     * APIProperty: attribution
     * {String} Attribution string, displayed when an 
     *     <OpenLayers.Control.Attribution> has been added to the map.
     */
    attribution: null, 

    /** 
     * Property: inRange
     * {Boolean} The current map resolution is within the layer's min/max 
     *     range. This is set in <OpenLayers.Map.setCenter> whenever the zoom 
     *     changes.
     */
    inRange: false,
    
    /**
     * Propery: imageSize
     * {<OpenLayers.Size>} For layers with a gutter, the image is larger than 
     *     the tile by twice the gutter in each dimension.
     */
    imageSize: null,
    
    /**
     * Property: imageOffset
     * {<OpenLayers.Pixel>} For layers with a gutter, the image offset 
     *     represents displacement due to the gutter.
     */
    imageOffset: null,

  // OPTIONS

    /** 
     * Property: options
     * {Object} An optional object whose properties will be set on the layer.
     *     Any of the layer properties can be set as a property of the options
     *     object and sent to the constructor when the layer is created.
     */
    options: null,

    /**
     * APIProperty: gutter
     * {Integer} Determines the width (in pixels) of the gutter around image
     *     tiles to ignore.  By setting this property to a non-zero value,
     *     images will be requested that are wider and taller than the tile
     *     size by a value of 2 x gutter.  This allows artifacts of rendering
     *     at tile edges to be ignored.  Set a gutter value that is equal to
     *     half the size of the widest symbol that needs to be displayed.
     *     Defaults to zero.  Non-tiled layers always have zero gutter.
     */ 
    gutter: 0, 

    /**
     * APIProperty: projection
     * {String} Set in the layer options to override the default projection
     *     string this layer - also set maxExtent, maxResolution, and units if
     *     appropriate.
     */
    projection: null,    
    
    /**
     * APIProperty: units
     * {String} The layer map units.  Defaults to 'degrees'.  Possible values
     *     are 'degrees' (or 'dd'), 'm', 'ft', 'km', 'mi', 'inches'.
     */
    units: null,

    /**
     * APIProperty: scales
     * {Array}  An array of map scales in descending order.  The values in the
     *     array correspond to the map scale denominator.  Note that these
     *     values only make sense if the display (monitor) resolution of the
     *     client is correctly guessed by whomever is configuring the
     *     application.  In addition, the units property must also be set.
     *     Use <resolutions> instead wherever possible.
     */
    scales: null,

    /**
     * APIProperty: resolutions
     * {Array} A list of map resolutions (map units per pixel) in descending
     *     order.  If this is not set in the layer constructor, it will be set
     *     based on other resolution related properties (maxExtent,
     *     maxResolution, maxScale, etc.).
     */
    resolutions: null,
    
    /**
     * APIProperty: maxExtent
     * {<OpenLayers.Bounds>}  The center of these bounds will not stray outside
     *     of the viewport extent during panning.  In addition, if
     *     <displayOutsideMaxExtent> is set to false, data will not be
     *     requested that falls completely outside of these bounds.
     */
    maxExtent: null,
    
    /**
     * APIProperty: minExtent
     * {<OpenLayers.Bounds>}
     */
    minExtent: null,
    
    /**
     * APIProperty: maxResolution
     * {Float} Default max is 360 deg / 256 px, which corresponds to
     *     zoom level 0 on gmaps.  Specify a different value in the layer 
     *     options if you are not using a geographic projection and 
     *     displaying the whole world.
     */
    maxResolution: null,

    /**
     * APIProperty: minResolution
     * {Float}
     */
    minResolution: null,

    /**
     * APIProperty: numZoomLevels
     * {Integer}
     */
    numZoomLevels: null,
   
    /**
     * APIProperty: minScale
     * {Float}
     */
    minScale: null,
    
    /**
     * APIProperty: maxScale
     * {Float}
     */
    maxScale: null,

    /**
     * APIProperty: displayOutsideMaxExtent
     * {Boolean} Request map tiles that are completely outside of the max 
     *     extent for this layer. Defaults to false.
     */
    displayOutsideMaxExtent: false,

    /**
     * APIProperty: wrapDateLine
     * {Boolean} #487 for more info.   
     */
    wrapDateLine: false,
    
    
    /**
     * Constructor: OpenLayers.Layer
     *
     * Parameters:
     * name - {String} The layer name
     * options - {Object} Hashtable of extra options to tag onto the layer
     */
    initialize: function(name, options) {

        this.addOptions(options);

        this.name = name;
        
        if (this.id == null) {

            this.id = OpenLayers.Util.createUniqueID(this.CLASS_NAME + "_");

            this.div = OpenLayers.Util.createDiv();
            this.div.style.width = "100%";
            this.div.style.height = "100%";
            this.div.id = this.id;

            this.events = new OpenLayers.Events(this, this.div, 
                                                this.EVENT_TYPES);
        }

        if (this.wrapDateLine) {
            this.displayOutsideMaxExtent = true;
        }
    },
    
    /**
     * Method: destroy
     * Destroy is a destructor: this is to alleviate cyclic references which
     *     the Javascript garbage cleaner can not take care of on its own.
     *
     * Parameters:
     * setNewBaseLayer - {Boolean} Set a new base layer when this layer has
     *     been destroyed.  Default is true.
     */
    destroy: function(setNewBaseLayer) {
        if (setNewBaseLayer == null) {
            setNewBaseLayer = true;
        }
        if (this.map != null) {
            this.map.removeLayer(this, setNewBaseLayer);
        }
        this.map = null;
        this.name = null;
        this.div = null;
        this.options = null;

        if (this.events) {
            this.events.destroy();
        }
        this.events = null;
    },
    
   /**
    * Method: clone
    *
    * Parameters:
    * obj - {<OpenLayers.Layer>} The layer to be cloned
    *
    * Returns:
    * {<OpenLayers.Layer>} An exact clone of this <OpenLayers.Layer>
    */
    clone: function (obj) {
        
        if (obj == null) {
            obj = new OpenLayers.Layer(this.name, this.options);
        } 
        
        // catch any randomly tagged-on properties
        OpenLayers.Util.applyDefaults(obj, this);
        
        // a cloned layer should never have its map property set
        //  because it has not been added to a map yet. 
        obj.map = null;
        
        return obj;
    },
    
    /** 
     * APIMethod: setName
     * Sets the new layer name for this layer.  Can trigger a changelayer event
     *     on the map.
     *
     * Parameters:
     * newName - {String} The new name.
     */
    setName: function(newName) {
        if (newName != this.name) {
            this.name = newName;
            if (this.map != null) {
                this.map.events.triggerEvent("changelayer");
            }
        }
    },    
    
   /**
    * APIMethod: addOptions
    * 
    * Parameters:
    * newOptions - {Object}
    */
    addOptions: function (newOptions) {
        
        if (this.options == null) {
            this.options = {};
        }
        
        // update our copy for clone
        OpenLayers.Util.extend(this.options, newOptions);

        // add new options to this
        OpenLayers.Util.extend(this, newOptions);
    },
    
    /**
     * APIMethod: onMapResize
     * This function can be implemented by subclasses
     */
    onMapResize: function() {
        //this function can be implemented by subclasses  
    },

    /**
     * APIMethod: redraw
     * Redraws the layer.  Returns true if the layer was redrawn, false if not.
     *
     * Returns:
     * {Boolean} The layer was redrawn.
     */
    redraw: function() {
        var redrawn = false;
        if (this.map) {

            // min/max Range may have changed
            this.inRange = this.calculateInRange();

            // map's center might not yet be set
            var extent = this.getExtent();

            if (extent && this.inRange && this.visibility) {
                this.moveTo(extent, true, false);
                redrawn = true;
            }
        }
        return redrawn;
    },

    /**
     * Method: moveTo
     * 
     * Parameters:
     * bound - {<OpenLayers.Bounds>}
     * zoomChanged - {Boolean} Tells when zoom has changed, as layers have to
     *     do some init work in that case.
     * dragging - {Boolean}
     */
    moveTo:function(bounds, zoomChanged, dragging) {
        var display = this.visibility;
        if (!this.isBaseLayer) {
            display = display && this.inRange;
        }
        this.display(display);
    },

    /**
     * Method: setMap
     * Set the map property for the layer. This is done through an accessor
     *     so that subclasses can override this and take special action once 
     *     they have their map variable set. 
     * 
     *     Here we take care to bring over any of the necessary default 
     *     properties from the map. 
     * 
     * Parameters:
     * map - {<OpenLayers.Map>}
     */
    setMap: function(map) {
        if (this.map == null) {
        
            this.map = map;
            
            // grab some essential layer data from the map if it hasn't already
            //  been set
            this.maxExtent = this.maxExtent || this.map.maxExtent;
            this.projection = this.projection || this.map.projection;
            this.units = this.units || this.map.units;
            
            this.initResolutions();
            
            if (!this.isBaseLayer) {
                this.inRange = this.calculateInRange();
                var show = ((this.visibility) && (this.inRange));
                this.div.style.display = show ? "" : "none";
            }
            
            // deal with gutters
            this.setTileSize();
        }
    },
    
    /**
     * APIMethod: removeMap
     * Just as setMap() allows each layer the possibility to take a 
     *     personalized action on being added to the map, removeMap() allows
     *     each layer to take a personalized action on being removed from it. 
     *     For now, this will be mostly unused, except for the EventPane layer,
     *     which needs this hook so that it can remove the special invisible
     *     pane. 
     * 
     * Parameters:
     * map - {<OpenLayers.Map>}
     */
    removeMap: function(map) {
        //to be overridden by subclasses
    },
    
    /**
     * APIMethod: getImageSize
     * 
     * Returns:
     * {<OpenLayers.Size>} The size that the image should be, taking into 
     *     account gutters.
     */ 
    getImageSize: function() { 
        return (this.imageSize || this.tileSize); 
    },    
  
    /**
     * APIMethod: setTileSize
     * Set the tile size based on the map size.  This also sets layer.imageSize
     *     and layer.imageOffset for use by Tile.Image.
     * 
     * Parameters: