Finding out the extent of the default zoom levels of OpenLayers

Question

I'd like to reproduce the zoom levels of OpenLayers in PostGIS. I am not used to working with JavaScript and am having difficulties to find out the exact extent in meters of the default zoom levels of OpenLayers. I can't find it anywhere on the internet.

With the function ST_Expand I can create a shape similar to a zoom level. I would like to use that function and recreate the default zoom levels 12, 13 and 14 of OpenLayers. How do I do that?

I am thinking of finding out the distance of the extent from OpenLayers, and using that as an input for the function ST_Expand. But how do I find that distance?

Answer 1

You can get extent of map and zoom level using openlayers:(you must work with javascript for finding extent of map and zoom levels)

var zoom = map.getZoom();
// perhaps scale can help you for finding distance.
var scale = map.getScale();
var pageExtent = map.getExtent();

and you can find distance with map extent and zoom level.

i hope can help you.