Which conditions does the geoJSON file read from the server in?

Question

I've added an alert to the function myReadFunction in order to detect function calls.

As according to my observations, the function readMyFunction is called sometimes while I have been navigating on the map, not every time. The function readMyFunction has not been called when a feature is being viewable or not during map navigation. Could you please explain in which conditions the geoJSON file is read from the server?

 mVectorLayer = new OpenLayers.Layer.Vector("Overlay", {
        strategies: [new OpenLayers.Strategy.BBOX()],
        protocol: new OpenLayers.Protocol.HTTP({
            url: 'http://localhost:56786/jlist.geojson',
            format: new OpenLayers.Format.GeoJSON({
                'read': myReadFunction,
                'internalProjection': map.baseLayer.projection,
                'externalProjection': new OpenLayers.Projection("EPSG:4326")
            })
        }),
        projection: new OpenLayers.Projection("EPSG:900913")
    });

Thanks a lot for your helps and clarifications

Answer 1

OpenLayers.Strategy.BBOX : Rreads new features when the viewport invalidates some bounds.

Try adjusting the resFactor {Float}

Optional factor used to determine when previously requested features are invalid. If set, the resFactor will be compared to the resolution of the previous request to the current map resolution. If resFactor > (old / new) and 1/resFactor < (old / new). If you set a resFactor of 1, data will be requested every time the resolution changes. If you set a resFactor of 3, data will be requested if the old resolution is 3 times the new, or if the new is 3 times the old. If the old bounds do not contain the new bounds new data will always be requested (with or without considering resFactor).

You can also play around with the ratio to see if this helps. Default is 2.