SURFACE — Surface (TIN)

Builds the digital terrain model by triangulating the selected points.

• Command: SURFACE · Global name: _SURFACE · Alias: TIN, MDT
• Ribbon: Topography › Terrain

Builds the digital terrain model (TIN) by Delaunay-triangulating points with elevation, with breaklines forced as edges, an outer boundary, holes and a maximum edge length. The surface is stored as a 3D face mesh that the viewer draws and that the contour lines are generated from.

Usage

1. Enter SURFACE (MDT) or click Surface (TIN).

Select the terrain points (points, blocks or a surface):

2. Select the entities with elevation: points, blocks (their insertion point is used) or an existing surface. Press Enter.

Select breaklines <none>:

3. Select the breaklines: 3D polylines, 2D polylines (at their elevation) or lines. Their segments become mesh edges: the surface folds along them (top and toe of a slope, edge of a wall, ditch line). Enter, none.

Select outer boundary <none>:

4. Select the outer boundary (closed polyline): triangles outside it are discarded. Enter, the whole hull of the points.

Select holes <none>:

5. Select the holes (closed polylines): areas with no surface inside the boundary, such as a building or a pond.

Maximum edge length (0 no limit) <…>:

6. Give the maximum edge length: border triangles with an exposed edge longer than that are removed, so distant points are not joined. 0, no limit.

Notes

• The Z of each entity is its elevation; points that coincide in plan are merged. Where two breaklines cross, a vertex is created with the elevation of the second one.
• A breakline whose vertices are all at elevation 0 is taken as a breakline without elevation: it forces the edge and takes the terrain elevations. The boundary and holes also take the terrain elevation.
• The mesh is a PolyfaceMesh that any DWG program reads. A model with more than 32,767 vertices or faces (the format limit) is stored as several meshes, in strips, which are selected and edited as one.
• The constraints are stored with the mesh (in its extension dictionary, record LINCE_MDT): they survive saving and opening the DWG and allow editing it with EDITSURFACE.
• For contours, select this surface in CONTOUR: its breaklines are respected.

See also

EDITSURFACE · CONTOUR · SPOTELEVATION · POINT