Make a TIN follow a breakline

A breakline is a polyline whose segments are forced into the TIN as constrained edges. Use one where the slope breaks — top of bank, bottom of bank, pavement edge, ridge, swale — and the triangulation has to follow that line. A constrained edge is not flipped by a later swap-edge or delete-line.

Add the breakline

1. Draw a polyline along the feature.
2. Select the polyline.
3. Run SURFADDBREAKLINE (alias SAB), or right-click the surface's Definition node in the Civil Prospector and choose Add Breakline....

The surface keeps its own copy of the geometry. Editing or deleting the source polyline afterwards leaves the breakline in place. Each vertex snaps to an existing TIN point within 1 cm, or is inserted when no point is that close. The segments between those vertices become the constrained edges.

When the triangles still cross the line

• The command was run with nothing selected, or the selection was not a polyline. Draw the feature as a polyline and select it before SAB.
• The edge you are looking at belongs to another surface. The breakline is listed under that surface's Definition › Breaklines (N) node, not as a loose polyline.
• The line was deleted from the Prospector. Removing the breakline drops the constraints. Points it inserted stay in the TIN, and those edges are free to flip again.
• You are looking at the source polyline, which no longer drives the surface. The stored breakline is drawn in the surface style. The default colour is magenta, on the Surface/Breakline component layer (default suffix BRKL, so C-TOPO-BRKL when the civil object layers are on). The Breaklines tab of the Surface Style editor sets visibility, colour, weight and linetype.