source: extensions/rv_gmaps/trunk/template/data_loader.js @ 12700

function PwgDataLoader( map, opts )
{
        this._map = map;
        this.options = jQuery.fn.extend(
                {
                        reload_data_timeout: 200,
                        rectangle_of_confusion: new google.maps.Size(32,16)
                }
                , opts || {} );
        this.options.rectangle_of_confusion = new google.maps.Size( this.options.rectangle_of_confusion.width, this.options.rectangle_of_confusion.height );
        if (this.options.rectangle_of_confusion.width<16) this.options.rectangle_of_confusion.width=16;
        if (this.options.rectangle_of_confusion.height<16) this.options.rectangle_of_confusion.height=16;
}


// returns the number of digits (between 0 and 6) to round a lat/lon so that it does not vary by more than factor*pow(-exp)
getLatLonDigits = function(d, factor, exp)
{
        if (d<0) return getLatLonDigits(-d,factor,exp);
        var digits = Math.ceil( exp - Math.log(d*factor)/Math.LN10 );
        return digits<0 ? 0 : (digits>6 ? 6 : digits);
}

Math.roundN = function(d, digits) { var c = Math.pow(10,digits); return Math.round(d*c)/c; }


PwgDataLoader.prototype =  {


_urlMapData: null,
_timerReloadData: null,
_dataLoading: false,

_previousLoadDataReq : {box: null, zoom:0, resultBounds:null},

start: function(urlMapData)
{
        this._urlMapData = urlMapData;
        google.maps.event.bind( this._map, "movestart", this, this.clearTimerReloadData );
        google.maps.event.bind( this._map, "idle", this, this._onIdle );
        //this._loadData();
},

terminate: function()
{
        this.clearTimerReloadData();
        this._map = null;
},

clearTimerReloadData : function()
{
        if (this._timerReloadData)
        {
                clearTimeout( this._timerReloadData );
                this._timerReloadData = null;
                return true;
        }
        return false;
},

_onIdle: function()
{
        this.clearTimerReloadData();
        this._timerReloadData = setTimeout(  pwgBind(this, this._onTimeoutLoadData), this.options.reload_data_timeout );
},


_onTimeoutLoadData: function ()
{
        if (this._dataLoading) return; // still in progress
        this.clearTimerReloadData();
        this._loadData();
},

_loadData: function()
{
        var bounds = this._map.getBounds();

        var latRange = bounds.toSpan().lat();
        var latPrec = latRange * this.options.rectangle_of_confusion.height / this._map.getDiv().offsetHeight;

        var lonRange = bounds.toSpan().lng();
        var lonPrec = ( lonRange>=0 ? lonRange : 360-lonRange )* this.options.rectangle_of_confusion.width / this._map.getDiv().offsetWidth;

        if ( this._previousLoadDataReq.box!=null )
        { // not the first time
                if ( this._previousLoadDataReq.box.contains( bounds.getNorthEast() )
                                        && this._previousLoadDataReq.box.contains( bounds.getSouthWest() ))
                {
                        if ( this._previousLoadDataReq.resultBounds == null )
                                return; // no images here
                        if ( this._map.getZoom() <= this._previousLoadDataReq.zoom )
                                return;
                }
        }

        var nd=0, sd=0, ed=0, wd=0;
        /*if ( !bounds.isFullLat() )*/
        {
                nd = latRange*12/100;
                sd = latRange*4/100;
        }
        /*if ( !bounds.isFullLng() )*/
        {
                ed = lonRange*9/100;
                wd = lonRange*7/100;
        }
        var digits = Math.max( getLatLonDigits(latRange,4,2), getLatLonDigits(lonRange,4,2) );
        var box = new google.maps.LatLngBounds( bounds.getSouthWest(), bounds.getNorthEast() );
        box.extend( new google.maps.LatLng( Math.roundN(bounds.getSouthWest().lat()-sd,digits), Math.roundN( bounds.getSouthWest().lng()-wd,digits ) ) );
        box.extend( new google.maps.LatLng( Math.roundN(bounds.getNorthEast().lat()+nd,digits), Math.roundN( bounds.getNorthEast().lng()+ed,digits) ) );

        var url = this._urlMapData;
        url += "&box=" + box.getSouthWest().toUrlValue(5) + "," + box.getNorthEast().toUrlValue(5);
        url += "&lap=" +  Math.roundN( latPrec, getLatLonDigits(latPrec,1,1) ).toString();
        url += "&lop=" +  Math.roundN( lonPrec, getLatLonDigits(lonPrec,1,1) ).toString();

        if (document.is_debug) {
                glog("sd="+sd+" wd="+wd+" nd="+nd+" ed="+ed);
                glog( url );
        }

        this._previousLoadDataReq.box = box;
        this._previousLoadDataReq.zoom = this._map.getZoom();
        this._previousLoadDataReq.resultBounds = null;
        this._dataLoading = true;

        try {
                google.maps.event.trigger( this, "dataloading" );
                jQuery.ajax( {
                        url: url,
                        success: pwgBind(this, this._onAjaxSuccess),
                        error: pwgBind(this, this._onAjaxError),
                        });
        }
        catch (e) {
                this._dataLoading = false;
                this._previousLoadDataReq.box=null;
                google.maps.event.trigger( this, "dataloadfailed", 600, e );
        }
},

_onAjaxSuccess: function(data, textStatus, xhr)
{
        var resp;
        try
        {
                eval('resp = ' + data);
                if (resp.nb_items == undefined)
                        throw new Error( "DATA DECODING ERROR" );
                this._previousLoadDataReq.resultBounds = resp.bounds;
                if (document.is_debug && resp.debug) glog( resp.debug );
                google.maps.event.trigger( this, "dataloaded", resp );
        }
        catch (e)       {
                this._previousLoadDataReq.box=null;
                google.maps.event.trigger( this, "dataloadfailed", responseCode, e );
                var s = e.message;
                s += '\n' + data.substr(0,1000);
                alert( s );
        }
        finally {
                this._dataLoading = false;
        }
},

_onAjaxError: function(xhr, textStatus, exc)
{
        try {
                google.maps.event.trigger( this, "dataloadfailed", textStatus + xhr.status, exc );
        }
        catch (e) {
        }
        finally {
                this._dataLoading = false;
        }
},

}