Editing the Terrain Model with Manual Tools

Once you've created a terrain model (DTM/TIN) based on survey data, you might need to refine or adjust it. This can include correcting inaccuracies, removing unwanted triangles (faces), or manually adding an elevation point.

The DTM tools in Pythagoras give you precise control over the triangulated surface, without altering the underlying survey objects such as points or breaklines. These tools are ideal for local cleanup, design adjustments, or preparing the model for cut/fill volume analysis.

Changes to a DTM are not undoable. Always save a backup before making manual edits.
These edits apply only to the terrain model itself — underlying points, lines or breaklines remain unchanged.

Tip: Planning an alternative terrain model (e.g. for cut and fill)? Copy your original DTM first, then apply these manual edits on the copy.

Menu: DTM > Tools

Swap Diagonal

Replaces the diagonal of two adjacent triangles with the opposite diagonal, effectively swapping the edge to change the triangulation locally.

• The cursor snaps to inner triangle edges (outer boundary edges are ignored).

• Click to perform the swap.

Delete Triangle

Removes a selected triangle (TIN face) from the active terrain model.

• Hover the cursor over a triangle to highlight it.

• Click to delete. The surface briefly flickers as confirmation.

• Any edges connected only to that triangle are also removed.

Move Vertex

Moves a vertex (point) within the DTM.

• The cursor snaps to existing vertices.

• Drag the point with the mouse or enter new X, Y, Z coordinates.

• A vertex cannot be moved outside the polygon of connected triangles.

Note: The updated triangulation is not guaranteed to remain Delaunay. Use other terrain tools if needed to improve the result.

Add Vertex

Adds a new vertex (point) to the terrain model.

• The cursor snaps to triangles or existing vertices.

• After selecting a triangle, a highlight appears. Click to manually enter X, Y, Z coordinates, or copy them from an existing point.

Notes:

The new point can also be placed outside the current model area.

The updated triangulation may not remain Delaunay. Refine with other tools if needed.

Delete Vertex

Deletes a vertex (point) and all connected triangles.

• The cursor snaps to vertices.

• Once selected, all connected triangles are removed.

• The remaining area is automatically retriangulated using the Delaunay method.

Change Elevation

Changes the elevation (Z-value of a point) of an existing vertex.

• The cursor snaps to vertices.

• Click a point to enter the new elevation in the Control Panel.