popup in openlayers

Question

What is the difference between popup and Frame and FrameColud?

And,it seems that the direction of the popup is depended on the location of the marker relatived to the map. The pop may be above or under the marker.

For example:

Above:

Below:

Now,I want to know how to make the popup always at the above of the marker?

Answer 1

Well,I answer this question myself.

You can override the calculateRelativePosition function for FramedCloud like this:

OpenLayers.FramedCloud.prototype.calculateRelativePosition=function(){
  return 'tr';
}

And this function is inherited from OpenLayers.Popup.Anchored.

calculateRelativePosition:function(px) {

var lonlat = this.map.getLonLatFromLayerPx(px);

var extent = this.map.getExtent();
var quadrant = extent.determineQuadrant(lonlat);

return OpenLayers.Bounds.oppositeQuadrant(quadrant); 

},