Rivers In Terrain

When building terrain by adding contour points from a map with the digitiser, it’s very difficult to get valley bottoms looking right.

In real life, most valleys have a river at their lowest point (unless you live in a chalk or limestone area…), so the best way to get that natural shape is to trace a river or stream from the map and then use this to define the terrain points forming the valley bottom.

Rivers in Rail3D are just represented as a track type for the moment.

  1. Select a suitable river or stream track type in the track settings dialogue
  2. Make sure ohle is switched off! Auto Cutting should be on, and Cutting Width should be about the same as the width of the river.
  3. In the digitiser, trace the course of the river between two points of known height on the map (e.g. spot heights, or contour lines crossing the river)
  4. Set the elevations of the two end nodes, and lock them.
  5. Put a marker on each end node
  6. Set and lock the elevations of a few intermediate nodes where the river crosses contour lines - rivers often have a steeper gradient in some places than in others. It is easier to do this if you place a text label near the desired point from the digitiser first.
  7. Run Grade Between Markers to smooth the gradient
  8. Go to the “upstream” marker, and place any suitable “train” on the track (I normally use the Kayak, but it really doesn’t matter) (if you don’t mind it running on a river, a landrover moves faster and goes up hills better)
  9. Select Terrain Setting Train on the Scenery menu, and select the options Set Terrain, Stitch and River. The River option creates terrain points alongside the river instead of in the centre and a metre of two higher. This should give the effect of the river running in a channel in the landscape.
  10. If you forgot to switch off ohle, you could also select Track Setting at this point to get rid of it…
  11. Start your “train”. As you head down the river, terrain points will be generated along the line of the river to pull the valley bottom into shape.
  12. Keep an eye on where the terrain points are — if you have used dem terrain you might have some terrain points close to the line of the river, which you can delete as you go along with the Terrain Eraser (otherwise you might get odd spikes or cliffs due to the inherent inaccuracy of the dem terrain)

This model of the Severn Valley around Highley in Shropshire was made using the technique described above:

Richard Southey