Also .. the "coarse" map models (linked in comment) are good for five years, the enhanced models less so .. and there's those other factors.
It's also a wee bit trickier than you might think to (say) fly a route and identify your location only from DTM contour path directly under craft. (Subsitute mag vectors for DTM values)
It's more like old school missile plotting via DTM's where a preprogrammed "follow this" path is generated to facilitate optimal "when the value rises, turn here" instructions .. which are great "recipe navigation" commands .. until something goes wrong, it strays too far off course and has to recover.
Identifying any position via a "random" 50 line km slice is a much harder problem.
See https://news.ycombinator.com/item?id=41188347 and realise that the EMM "high res" map has a wavelength of 50+km .. compare that to, say, old school LORAN positioning accuracy.
Also .. the "coarse" map models (linked in comment) are good for five years, the enhanced models less so .. and there's those other factors.
It's also a wee bit trickier than you might think to (say) fly a route and identify your location only from DTM contour path directly under craft. (Subsitute mag vectors for DTM values)
It's more like old school missile plotting via DTM's where a preprogrammed "follow this" path is generated to facilitate optimal "when the value rises, turn here" instructions .. which are great "recipe navigation" commands .. until something goes wrong, it strays too far off course and has to recover.
Identifying any position via a "random" 50 line km slice is a much harder problem.