layer.js

用来在地图上做操作GIS,在地图上做标记

     * size - {<OpenLayers.Size>}
     */
    setTileSize: function(size) {
        var tileSize = (size) ? size :
                                ((this.tileSize) ? this.tileSize :
                                                   this.map.getTileSize());
        this.tileSize = tileSize;
        if(this.gutter) {
          // layers with gutters need non-null tile sizes
          //if(tileSize == null) {
          //    OpenLayers.console.error("Error in layer.setMap() for " +
          //                              this.name + ": layers with " +
          //                              "gutters need non-null tile sizes");
          //}
            this.imageOffset = new OpenLayers.Pixel(-this.gutter, 
                                                    -this.gutter); 
            this.imageSize = new OpenLayers.Size(tileSize.w + (2*this.gutter), 
                                                 tileSize.h + (2*this.gutter)); 
        }
    },

    /**
     * APIMethod: getVisibility
     * 
     * Returns:
     * {Boolean} The layer should be displayed (if in range).
     */
    getVisibility: function() {
        return this.visibility;
    },

    /** 
     * APIMethod: setVisibility
     * Set the visibility flag for the layer and hide/show & redraw 
     *     accordingly. Fire event unless otherwise specified
     * 
     * Note that visibility is no longer simply whether or not the layer's
     *     style.display is set to "block". Now we store a 'visibility' state 
     *     property on the layer class, this allows us to remember whether or 
     *     not we *desire* for a layer to be visible. In the case where the 
     *     map's resolution is out of the layer's range, this desire may be 
     *     subverted.
     * 
     * Parameters:
     * visible - {Boolean} Whether or not to display the layer (if in range)
     */
    setVisibility: function(visibility) {
        if (visibility != this.visibility) {
            this.visibility = visibility;
            this.display(visibility);
            this.redraw();
            if (this.map != null) {
                this.map.events.triggerEvent("changelayer");
            }
            this.events.triggerEvent("visibilitychanged");
        }
    },

    /** 
     * APIMethod: display
     * Hide or show the Layer
     * 
     * Parameters:
     * display - {Boolean}
     */
    display: function(display) {
        if (display != (this.div.style.display != "none")) {
            this.div.style.display = (display) ? "block" : "none";
        }
    },

    /**
     * Method: calculateInRange
     * 
     * Returns:
     * {Boolean} The layer is displayable at the current map's current
     *     resolution.
     */
    calculateInRange: function() {
        var inRange = false;
        if (this.map) {
            var resolution = this.map.getResolution();
            inRange = ( (resolution >= this.minResolution) &&
                        (resolution <= this.maxResolution) );
        }
        return inRange;
    },

    /** 
     * APIMethod: setIsBaseLayer
     * 
     * Parameters:
     * isBaseLayer - {Boolean}
     */
    setIsBaseLayer: function(isBaseLayer) {
        if (isBaseLayer != this.isBaseLayer) {
            this.isBaseLayer = isBaseLayer;
            if (this.map != null) {
                this.map.events.triggerEvent("changelayer");
            }
        }
    },

  /********************************************************/
  /*                                                      */
  /*                 Baselayer Functions                  */
  /*                                                      */
  /********************************************************/
  
    /** 
     * Method: initResolutions
     * This method's responsibility is to set up the 'resolutions' array 
     *     for the layer -- this array is what the layer will use to interface
     *     between the zoom levels of the map and the resolution display 
     *     of the layer.
     * 
     * The user has several options that determine how the array is set up.
     *  
     * For a detailed explanation, see the following wiki from the 
     *     openlayers.org homepage:
     *     http://trac.openlayers.org/wiki/SettingZoomLevels
     */
    initResolutions: function() {

        // These are the relevant options which are used for calculating 
        //  resolutions information.
        //
        var props = new Array(
          'projection', 'units',
          'scales', 'resolutions',
          'maxScale', 'minScale', 
          'maxResolution', 'minResolution', 
          'minExtent', 'maxExtent',
          'numZoomLevels', 'maxZoomLevel'
        );

        // First we create a new object where we will store all of the 
        //  resolution-related properties that we find in either the layer's
        //  'options' array or from the map.
        //
        var confProps = {};        
        for(var i=0; i < props.length; i++) {
            var property = props[i];
            confProps[property] = this.options[property] || this.map[property];
        }

        // If numZoomLevels hasn't been set and the maxZoomLevel *has*, 
        //  then use maxZoomLevel to calculate numZoomLevels
        //
        if ( (!confProps.numZoomLevels) && (confProps.maxZoomLevel) ) {
            confProps.numZoomLevels = confProps.maxZoomLevel + 1;
        }

        // First off, we take whatever hodge-podge of values we have and 
        //  calculate/distill them down into a resolutions[] array
        //
        if ((confProps.scales != null) || (confProps.resolutions != null)) {
          //preset levels
            if (confProps.scales != null) {
                confProps.resolutions = [];
                for(var i = 0; i < confProps.scales.length; i++) {
                    var scale = confProps.scales[i];
                    confProps.resolutions[i] = 
                       OpenLayers.Util.getResolutionFromScale(scale, 
                                                              confProps.units);
                }
            }
            confProps.numZoomLevels = confProps.resolutions.length;

        } else {
          //maxResolution and numZoomLevels based calculation
            
            confProps.resolutions = [];
            
            // determine maxResolution
            if (confProps.minScale) {
                confProps.maxResolution = 
                    OpenLayers.Util.getResolutionFromScale(confProps.minScale, 
                                                           confProps.units);
            } else if (confProps.maxResolution == "auto") {
                var viewSize = this.map.getSize();
                var wRes = confProps.maxExtent.getWidth() / viewSize.w;
                var hRes = confProps.maxExtent.getHeight()/ viewSize.h;
                confProps.maxResolution = Math.max(wRes, hRes);
            } 

            // determine minResolution
            if (confProps.maxScale != null) {           
                confProps.minResolution = 
                    OpenLayers.Util.getResolutionFromScale(confProps.maxScale);
            } else if ( (confProps.minResolution == "auto") && 
                        (confProps.minExtent != null) ) {
                var viewSize = this.map.getSize();
                var wRes = confProps.minExtent.getWidth() / viewSize.w;
                var hRes = confProps.minExtent.getHeight()/ viewSize.h;
                confProps.minResolution = Math.max(wRes, hRes);
            } 

            // determine numZoomLevels
            if (confProps.minResolution != null) {
                var ratio = confProps.maxResolution / confProps.minResolution;
                confProps.numZoomLevels = 
                    Math.floor(Math.log(ratio) / Math.log(2)) + 1;
            }
            
            // now we have numZoomLevels and maxResolution, 
            //  we can populate the resolutions array
            for (var i=0; i < confProps.numZoomLevels; i++) {
                var res = confProps.maxResolution / Math.pow(2, i)
                confProps.resolutions.push(res);
            }    
        }
        
        //sort resolutions array ascendingly
        //
        confProps.resolutions.sort( function(a, b) { return(b-a); } );

        // now set our newly calculated values back to the layer 
        //  Note: We specifically do *not* set them to layer.options, which we 
        //        will preserve as it was when we added this layer to the map. 
        //        this way cloned layers reset themselves to new map div 
        //        dimensions)
        //

        this.resolutions = confProps.resolutions;
        this.maxResolution = confProps.resolutions[0];
        var lastIndex = confProps.resolutions.length - 1;
        this.minResolution = confProps.resolutions[lastIndex];
        
        this.scales = [];
        for(var i = 0; i < confProps.resolutions.length; i++) {
            this.scales[i] = 
               OpenLayers.Util.getScaleFromResolution(confProps.resolutions[i], 
                                                      confProps.units);
        }
        this.minScale = this.scales[0];
        this.maxScale = this.scales[this.scales.length - 1];
        
        this.numZoomLevels = confProps.numZoomLevels;
    },

    /**
     * APIMethod: getResolution
     * 
     * Returns:
     * {Float} The currently selected resolution of the map, taken from the
     *     resolutions array, indexed by current zoom level.
     */
    getResolution: function() {
        var zoom = this.map.getZoom();
        return this.resolutions[zoom];
    },

    /** 
     * APIMethod: getExtent
     * 
     * Returns:
     * {<OpenLayers.Bounds>} A Bounds object which represents the lon/lat 
     *     bounds of the current viewPort.
     */
    getExtent: function() {
        // just use stock map calculateBounds function -- passing no arguments
        //  means it will user map's current center & resolution
        //
        return this.map.calculateBounds();
    },

    /**
     * APIMethod: getZoomForExtent
     * 
     * Parameters:
     * bounds - {<OpenLayers.Bounds>}
     * closest - {Boolean} Find the zoom level that most closely fits the 
     *     specified bounds. Note that this may result in a zoom that does 
     *     not exactly contain the entire extent.
     *     Default is false.
     *
     * Returns:
     * {Integer} The index of the zoomLevel (entry in the resolutions array) 
     *     for the passed-in extent. We do this by calculating the ideal 
     *     resolution for the given extent (based on the map size) and then 
     *     calling getZoomForResolution(), passing along the 'closest'
     *     parameter.
     */
    getZoomForExtent: function(extent, closest) {
        var viewSize = this.map.getSize();
        var idealResolution = Math.max( extent.getWidth()  / viewSize.w,
                                        extent.getHeight() / viewSize.h );

        return this.getZoomForResolution(idealResolution, closest);
    },
    
    /** 
     * Method: getDataExtent
     * Calculates the max extent which includes all of the data for the layer.
     *     This function is to be implemented by subclasses.
     * 
     * Returns:
     * {<OpenLayers.Bounds>}
     */
    getDataExtent: function () {
        //to be implemented by subclasses
    },

    /**
     * APIMethod: getZoomForResolution
     * 
     * Parameters:
     * resolution - {Float}
     * closest - {Boolean} Find the zoom level that corresponds to the absolute 
     *     closest resolution, which may result in a zoom whose corresponding
     *     resolution is actually smaller than we would have desired (if this
     *     is being called from a getZoomForExtent() call, then this means that
     *     the returned zoom index might not actually contain the entire 
     *     extent specified... but it'll be close).
     *     Default is false.
     * 
     * Returns:
     * {Integer} The index of the zoomLevel (entry in the resolutions array) 
     *     that corresponds to the best fit resolution given the passed in 
     *     value and the 'closest' specification.
     */
    getZoomForResolution: function(resolution, closest) {
        var diff;
        var minDiff = Number.POSITIVE_INFINITY;
        for(var i=0; i < this.resolutions.length; i++) {            
            if (closest) {
                diff = Math.abs(this.resolutions[i] - resolution);
                if (diff > minDiff) {
                    break;
                }
                minDiff = diff;
            } else {
                if (this.resolutions[i] < resolution) {
                    break;
                }
            }
        }
        return Math.max(0, i-1);
    },
    
    /**
     * APIMethod: getLonLatFromViewPortPx
     * 
     * Parameters:
     * viewPortPx - {<OpenLayers.Pixel>}
     *
     * Returns:
     * {<OpenLayers.LonLat>} An OpenLayers.LonLat which is the passed-in 
     *     view port <OpenLayers.Pixel>, translated into lon/lat by the layer.
     */
    getLonLatFromViewPortPx: function (viewPortPx) {
        var lonlat = null;
        if (viewPortPx != null) {
            var size = this.map.getSize();
            var center = this.map.getCenter();
            if (center) {
                var res  = this.map.getResolution();
        
                var delta_x = viewPortPx.x - (size.w / 2);
                var delta_y = viewPortPx.y - (size.h / 2);
            
                lonlat = new OpenLayers.LonLat(center.lon + delta_x * res ,
                                             center.lat - delta_y * res); 

                if (this.wrapDateLine) {
                    lonlat = lonlat.wrapDateLine(this.maxExtent);
                }
            } // else { DEBUG STATEMENT }
        }
        return lonlat;
    },

    /**
     * APIMethod: getViewPortPxFromLonLat
     * 
     * Parameters:
     * lonlat - {<OpenLayers.LonLat>}
     *
     * Returns: 
     * {<OpenLayers.Pixel>} An <OpenLayers.Pixel> which is the passed-in 
     *     <OpenLayers.LonLat>,translated into view port pixels.
     */
    getViewPortPxFromLonLat: function (lonlat) {
        var px = null; 
        if (lonlat != null) {
            var resolution = this.map.getResolution();
            var extent = this.map.getExtent();
            px = new OpenLayers.Pixel(
                Math.round(1/resolution * (lonlat.lon - extent.left)),
                Math.round(1/resolution * (extent.top - lonlat.lat))
            );    
        }
        return px;
    },
    
    /**
     * APIMethod: setOpacity
     * Sets the opacity for the entire layer (all images)
     * 
     * Parameter:
     * opacity - {Float}
     */
    setOpacity: function(opacity) {
        if (opacity != this.opacity) {
            this.opacity = opacity;
            for(var i=0; i<this.div.childNodes.length; ++i) {
                var element = this.div.childNodes[i].firstChild;
                OpenLayers.Util.modifyDOMElement(element, null, null, null, 
                                                 null, null, null, opacity);
            }
        }
    },

    /**
     * Method: setZIndex
     * 
     * Parameters: 
     * zIndex - {Integer}
     */    
    setZIndex: function (zIndex) {
        this.div.style.zIndex = zIndex;
    },

    /**
     * Method: adjustBounds
     * This function will take a bounds, and if wrapDateLine option is set
     *     on the layer, it will return a bounds which is wrapped around the 
     *     world. We do not wrap for bounds which *cross* the 
     *     maxExtent.left/right, only bounds which are entirely to the left 
     *     or entirely to the right.
     * 
     * Parameters:
     * bounds - {<OpenLayers.Bounds>}
     */
    adjustBounds: function (bounds) {

        if (this.gutter) {
            // Adjust the extent of a bounds in map units by the 
            // layer's gutter in pixels.
            var mapGutter = this.gutter * this.map.getResolution();
            bounds = new OpenLayers.Bounds(bounds.left - mapGutter,
                                           bounds.bottom - mapGutter,
                                           bounds.right + mapGutter,
                                           bounds.top + mapGutter);
        }

        if (this.wrapDateLine) {
            // wrap around the date line, within the limits of rounding error
            var wrappingOptions = { 
                'rightTolerance':this.getResolution()
            };    
            bounds = bounds.wrapDateLine(this.maxExtent, wrappingOptions);
                              
        }
        return bounds;
    },

    CLASS_NAME: "OpenLayers.Layer"
});