[OpenLayers-Users] externalGraphic anchoring points?

[William Martin]

All,

Hi, new user.  I'm using a vector layer for placing markers on the map, and I'm using the externalGraphic property to specify a marker of my own.  How is that image anchored with respect to the lat/lon coordinates that it represents?

That is, if exactly one pixel in the external graphic corresponds to the point on the map, is it:

a) The top left corner pixel
b) The top right corner pixel
c) The bottom left corner pixel
d) The bottom right corner pixel
e) The exact center pixel
f) A pixel halfway along one edge
Or g) something else entirely?

I need to know so that I can figure out the correct offsets to use with my graphic.

I tried to figure this out by using an external graphic for the marker which was a 1x1 pixel animated GIF blinking red/white/red/white and then defining another marker for the same coordinates with a translucent version of the regular image.  But the 1x1 graphic refused to show up, even when I disabled the other marker so that it was on its own.  Weird.

Thanks!

Will Martin
Web Services Librarian
Chester Fritz Library, University of North Dakota