TIN Surfaces

NullCad can build Triangulated Irregular Network (TIN) surfaces from selected points, using a Constrained Delaunay Triangulation, and display them as a triangle wireframe, as elevation contours, or both.

Creating a surface

1. Activate the TIN Surface tool (SURVEY toolbar group). The TIN panel opens on the right.
2. Select the points you want to triangulate (they must have Z values), then click Add Selected Points in the panel.
3. Optionally add breaklines: select exactly two points from the list and click Add Breakline from Selection.
4. Click Generate TIN Surface. At least 3 points with Z values are required, and the points must not all be collinear.

The surface is created as a single undoable operation on the active layer.

Display modes

Each surface has its own display settings, edited in the Properties panel and saved with the document:

• Triangles — wireframe of the triangulation edges (default).
• Contours — elevation contour lines derived from the mesh.
• Both — edges and contours together.

Contours are controlled by two per-surface values:

• Contour interval — vertical distance between levels, aligned to absolute multiples of the interval (an interval of 0.5 produces levels at …, 10.0, 10.5, 11.0, …).
• Major every — every Nth level is a major contour and is drawn at twice the line weight.

Contours update live when the surface or its settings change, and they follow the display mode in drafting viewports and PDF export. If the interval is small enough to produce more than 2000 levels, contours are hidden and the Properties panel explains why.

Extracting contours

Extract Contours to Polylines (Properties panel) creates one polyline geometry object per contour line, on the surface’s layer, with the contour elevation stored as the polyline’s Z value. The extraction is a single undoable operation. Extracted polylines are ordinary geometry — they can be edited and exported, but they do not update if the surface changes.

Regenerating

Regenerate from Source Points (Properties panel) rebuilds the triangulation from the current positions and elevations of the points the surface was created from. Deleted source points are dropped (at least 3 must remain), breaklines are remapped, and the display settings are kept. The regeneration is undoable.

Non-destructive

Building a TIN surface never modifies the source points — the surface is a separate geometry object (TinSurface) that stores its own copy of the vertex data and references the source point IDs for regeneration.

Breaklines

• Hard breaklines force triangle edges to follow the breakline exactly — used for discontinuities like retaining walls or building edges. Two hard breaklines may share endpoints but must not cross each other.
• Soft breaklines are stored with the surface but do not affect the triangulation; they are reserved for future interpolation features.

Snapping and selection

Endpoint snap targets the TIN’s vertices; midpoint, nearest, perpendicular, and intersection snaps target its triangulation edges. Clicking selects the surface by its displayed linework (edges and/or contours), as does rectangle selection.

Export

• PDF — the surface is drawn following its display mode, with major contours stroked heavier; this includes drafting viewports.
• DXF — the surface exports as one 3DFACE entity per triangle with true per-vertex elevations, readable by other CAD packages.
• Extracted contour polylines export like any other polyline (e.g. DXF polylines carrying their elevation).