private NestedPointFeatureCollection nextFilteredPointFeatureCollection() throws IOException {
if ( npfciter == null) return null;
if (!npfciter.hasNext()) return null;
NestedPointFeatureCollection pdata = npfciter.next();
if (!filter(pdata)) {
if (!npfciter.hasNext()) return null;
pdata = npfciter.next();
}