private void derive(Schema schema, DocumentSummary documentSummary) {
        if (documentSummary == null) return;
        for (SummaryField summaryField : documentSummary.getSummaryFields().values()) {
            List<String> from = toStringList(summaryField.sourceIterator());

            if (doMapField(schema, summaryField)) {
                SDField sdField = schema.getConcreteField(summaryField.getName());
                if (sdField != null && GeoPos.isAnyPos(sdField)) {
                    summaryMap.put(summaryField, List.of(summaryField.getName()));
                } else {
                    summaryMap.put(summaryField, from);
                }
            }
        }
    }
Vertical streaming matcher summary specification

@author bratseth
config-model/src/main/java/com/yahoo/schema/derived/VsmSummary.java