Robert, i think we need to approach the DTM from a new angle.
you and jeff should look and all the items placed on & in the earth, sidewalks, curbs, ADA sidewalks access, drains & piping, roads, parking, footings, slabs, gabions, foundations and anything else. then make very good tools to make those items.
THEN make it so the DTM melts upwards to fill in around those items. then when you cut a section the dtm shows and earth fill around those items.