Obtaining rendered data

[Ezhidze]

I am using a database (postgres), the map is rendered using mapnik. Unfortunately, I cannot choose another way.

Basically, I want to get a list of only those items that will be displayed at the selected zoom levels. I know that the data in the database is not marked with a zoom level; and that mapnik, based on the mapnik style file (xml), determines what will be displayed/rendered at a selected level and what will not.

But I cannot find a way (algorithm) to do this - how to calculate (and log/save) the items that will be displayed/rendered.