TIN surfaces on terraced ground
Dabbling with TIN surfaces. I have a piece of ground which is terraced.
The terrace ground surfaces are quite bumpy up-and-down, surveyed with plentiful spot levels marked on a plan grid.
Vertical retaining walls form vertical drops separating one terrace from the next, with no upstand; they wander, as drawn in plan.
The retaining walls' visible top and bottom edges also wander vertically, defined simply by where the vertical surface intersects with the abutting terrace ground surfaces.
Of course, a TIN surface built simply from the spot levels, blurs with a banked shape across the zones where the retaining walls would run.
How to insert the retaining walls as breaks, forming a sharp vertical step between one terrace ground surface and the next?
The spot levels grid comes close to the retaining walls but no spot points fall precisely on the line of the retaining walls, at either their top or bottom edge. I had hoped that the terrace ground surfaces would extrapolate beyond the nearest spot points, to define their intersection with the retaining walls' vertical surface.
I had assumed that 'break lines' (the line of the retaining walls on plan) would be treated as a vertical surface projected vertically from the plan drawing, which would create separated areas of terrace ground surface as defined solely by their spot levels.
Now it seems that 'break lines' means the retaining walls have to have their visible top and bottom edges levelled, and those levelled edges define triangle-edges both horizontal(ish) and vertical.
There must be a Surveyor's economical procedure for this, which my Architectural measuring-up skillset has never needed?