Agriculture Elevation Mapping for irrigation, drainage, and even landforming is all operated off of relative elevation. A base is set on an unknown point around the field being mapped. From there a rover collects elevation or provides a reading relative to the bases location. This practice is commonly used through ground marking/surveying; however with a drone you need real world horizontal accuracy without the need of real world vertical (MSL) which is the common purpose of ground control points (GCPs). The “Hybrid” method as I like to coin it is setting a base location using NTRIP corrections prior to flight with a EMLID receiver or doing a PPK method of processing. How relative can the base be? I’ve collected elevation on over 90,000 Acres across 3 years doing this right here!