Surfaces & volumes

Triangulated terrain models (TIN) for existing ground and design surfaces — and the earthwork between them.

What a surface is

A surface is a TIN — a Triangulated Irregular Network built from 3D points by Delaunay triangulation. Any (x, y) inside it interpolates an elevation from the triangle it falls in. Surfaces drive the ground line in Profile, the ground in Sections, daylighting, and cut/fill volumes.

Creating a surface

Command	Source
Surface from Point File…	Triangulate an imported point cloud (CSV / TXT / PTS), with a column-order choice.
Corridor Surface + Volume…	Build a TIN from a corridor's cross-sections and compute cut/fill (below).
Points group	A point group's points can be triangulated into a surface.

Breaklines

A breakline forces triangle edges to follow a line (a ridge, a ditch, an edge of pavement) instead of cutting across it. Tools › Add Surface Breakline prompts you to draw a polyline over the selected surface; press Esc to enforce it into the TIN. Corridor surfaces enforce their feature lines as breaklines automatically.

Surface Style

Tools › Surface Style sets the display mode and contours:

Mode	Draws
Border (outline)	Just the TIN perimeter.
Triangles (TIN)	All triangle edges.
Contours	Contour lines at the Minor interval (default 2 m); every Major every (default 5) is a bold major contour.

Surface History lists the construction steps so you can review or revert.

Corridor surfaces

From Corridor Properties › Surfaces (or Tools › Corridor Surface + Volume) you choose which feature-line codes contribute (none = every section point), and on Boundaries whether to clip the TIN to the corridor extents. A corridor surface stays linked to its corridor and rebuilds when the corridor changes.

Cut & fill volumes

Tools › Corridor Surface + Volume samples every corridor at 5 m, builds its TIN, and compares it to a ground surface on a regular grid. The report lists, per corridor:

{name} surface ({pts} pts, {tris} tris, {ok}/{total} breakline edges) — the breakline count flags a degenerate section if it's partial.
vs ground: cut {…} m³ fill {…} m³ net {…} m³.

Quantity	Meaning
Cut	Where existing ground is above the design (material removed).
Fill	Where the design is above ground (material added).
Net	Fill − cut — positive = net fill, negative = net cut.

The grid method and accuracy are in the Formula reference.

Import / export

Surfaces round-trip through LandXML (points + triangles) and export to DXF as 3D faces. See the Command reference.