Thank you very much for the kind comments. They are appreciated. The locale is produced in TRANSDEM from a 2m LIDAR DEM and a combination of 25 inch and 6 inch OS maps from the NLS. Some filling in from the OS 50m DEM is required as the OS rather snootily declined my application for a 5m Digital Terrain Model DEM package. I have been using the NER Gradient profiles from the NERA and it seems that this data also forms the basis for what appears in the Middleton press range of books on the East Coast Main line etc. However, the caution at the start of the NERA profiles by two NERA members with railway survey experience is manifestly warranted. The gradient from Bog Hall to Prospect Hill is 1:53 in the book but rather more like 1:45.5! Another glaring issue is the gradient north from Sandsend to the portal of Sandsend tunnel. The gradient profile says 1:57 whereas it is closer to 1:37. The 1:57 leaves the line 18m too low at the tunnel portal!!!! The 2m DTM is just not that inaccurate, since the cutting in the terrain leading to it is clearly visible on the DEM.
The limits of the DEM do play a part, since at each 2m sample point there is a range of vertical tolerance (1m in a 50m DEM, not sure what it is for the 2m DEM), though the DTM is overall rather consistent. Whitby Town is at an accurate DTM altitude.
I am experimenting with some concept partial/mini-routes. The DEM of NER territory in Yorkshire is at 16Gb and makes the gaming laptop work its socks off. The georeferenced raster maps aren't that far off 16Gb either. That is for the county. not a trainz route. Eventually, I intend to at least try and assemble a single DEM for the north of England (estimate 36 GB) and then produce an NER base route. From this I can extract sections which will all have the same origin in order to match up Trainz baseboards.
By doing this I am evaluating whether to suspend work on my NW Durham route (built initially in 2010 and based on a 2008/2010 era 1 second arc/50m DEM) and start work on the route working from a 2019 2m DEM. There is just too much work to do on the 50m vintage DEM route to bring it closer to modern standards and even then it is underneath still the 2008/2010 model.