In an example, a method includes acquiring, at a processor, object model data for an object to be generated in additive manufacturing, the object model data representing the object as a plurality of polygons. A virtual object space enclosing the object may be inspected from a plurality of discrete source points in a plane. For each of a plurality of distances from each source point, it may be determined if a polygon face is encountered, and if so, a counter may be set based on whether the polygon face is oriented towards the source point or away from the source point. Based on a content of the counter, it may be determined if a volume enclosed between two distances from a source point is a volume of the object.