The relation between the Feature's Geometry and its externalGraphic

Question

I wonder what is the relation between the Geometry.Point one sets for a Feature.Vector and the image provided as externalGraphic for the style, in OpenLayers.

Is the Geometry.Point of a feature for the image:

1. The centre point of the image,
2. or the left top most corner of the image.

In case it is 2 then please advice how would I set the values of offsets if, for example, the image is 32x32 (WxH). Is it simply 16 (W/2) for the value of graphicXOffset, and accordingly for the graphicYOffset?

I need to know this information to set the image centre to be the point of a feature. Sadly the documentation doesn't say a word about it, or I am unable to find it.

Answer 1

I figured out, using the code below, that the geometry point of a feature is the centre point of an image set using the externalGraphics. After adding a feature with an image I added another one with a style painting the point as a circle with radius of 5 and the point was painted in the middle of the image.

// World Geodetic System 1984 projection (lon/lat) -- set as the map's display projection
var projWGS84 = new OpenLayers.Projection("EPSG:4326"); 
// Spherical Mercator projection (meters) -- set as the map's projection
var proj900913 = new OpenLayers.Projection("EPSG:900913");
var origin = new OpenLayers.Geometry.Point(lon, lat).transform(projWGS84, map.getProjectionObject());
var style = {
   pointRadius: 5
};
var center = new OpenLayers.Feature.Vector(origin, null, style);
layer.addFeatures([center]);