gistfile1.js

  
    /** 
     * 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() {

        // ok we want resolutions, here's our strategy:
        //
        // 1. if resolutions are defined in the layer config, use them
        // 2. else, if scales are defined in the layer config then derive
        //    resolutions from these scales
        // 3. else, attempt to calculate resolutions from maxResolution,
        //    minResolution, numZoomLevels, maxZoomLevel set in the
        //    layer config
        // 4. if we still don't have resolutions, and if resolutions
        //    are defined in the same, use them
        // 5. else, if scales are defined in the map then derive
        //    resolutions from these scales
        // 6. else, attempt to calculate resolutions from maxResolution,
        //    minResolution, numZoomLevels, maxZoomLevel set in the
        //    map
        // 7. hope for the best!

        var i, len;
        var props = {}, alwaysInRange = true;

        // get resolution data from layer config
        // (we also set alwaysInRange in the layer as appropriate)
        for(i=0, len=this.RESOLUTION_PROPERTIES.length; i<len; i++) {
            var p = this.RESOLUTION_PROPERTIES[i]
            props[p] = this.options[p];
            if(alwaysInRange && this.options[p]) {
                alwaysInRange = false;
            }
        }
        if(this.alwaysInRange == null) {
            this.alwaysInRange = alwaysInRange;
        }

        // if we don't have resolutions then attempt to derive them from scales
        if(props.resolutions == null) {
            props.resolutions = this.resolutionsFromScales(props.scales);
        }

        // if we still don't have resolutions then attempt to calculate them
        if(props.resolutions == null) {
            props.resolutions = this.calculateResolutions(props);
        }

        // if we couldn't calculate resolutions then we look at we have
        // in the map
        if(props.resolutions == null) {
            for(i=0, len=this.RESOLUTION_PROPERTIES.length; i<len; i++) {
                var p = this.RESOLUTION_PROPERTIES[i]
                props[p] = this.options[p] != null ?
                    this.options[p] : this.map[p];
            }
            if(props.resolutions == null) {
                props.resolutions = this.resolutionsFromScales(props.scales);
            }
            if(props.resolutions == null) {
                props.resolutions = this.calculateResolutions(props);
            }
        }

        // ok, we new need to set properties in the instance

        // get maxResolution from the config if it's defined there
        var maxResolution;
        if(this.options.maxResolution &&
           this.options.maxResolution !== "auto") {
            maxResolution = this.options.maxResolution;
        }
        if(this.options.minScale) {
            maxResolution = OpenLayers.Util.getResolutionFromScale(
                this.options.minScale, this.units);
        }

        // get minResolution from the config if it's defined there
        var minResolution;
        if(this.options.minResolution &&
           this.options.minResolution !== "auto") {
            minResolution = this.options.minResolution;
        }
        if(this.options.maxScale) {
            minResolution = OpenLayers.Util.getResolutionFromScale(
                this.options.maxScale, this.units);
        }

        if(props.resolutions) {

            //sort resolutions array descendingly
            props.resolutions.sort(function(a, b) {
                return (b - a);
            });

            // if we still don't have a maxResolution get it from the
            // resolutions array
            if(!maxResolution) {
                maxResolution = props.resolutions[0];
            }

            // if we still don't have a minResolution get it from the
            // resolutions array
            if(!minResolution) {
                var lastIdx = props.resolutions.length - 1;
                minResolution = props.resolutions[lastIdx];
            }
        }

        this.resolutions = props.resolutions;
        if(this.resolutions) {
            len = this.resolutions.length;
            this.scales = new Array(len);
            for(i=0; i<len; i++) {
                this.scales[i] = OpenLayers.Util.getScaleFromResolution(
                    this.resolutions[i], this.units);
            }
            this.numZoomLevels = len;
        }
        this.minResolution = minResolution;
        if(minResolution) {
            this.maxScale = OpenLayers.Util.getScaleFromResolution(
                minResolution, this.units);
        }
        this.maxResolution = maxResolution;
        if(maxResolution) {
            this.minScale = OpenLayers.Util.getScaleFromResolution(
                maxResolution, this.units);
        }
    },