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DTM Tools workflow guide

Create and adjust
terrain breaklines

Start with 2D linework in the correct XY position, use DTM_DrapeCloud to read elevations from the point cloud, then correct individual vertices with Adjust Z before building the terrain surface. If a finished TIN already exists, use DTM_DrapeSurface to follow that triangulation exactly.

DTM_DrapeCloudDTM_DrapeSurfaceDTM_ADJUST_Z

Drape is the main breakline-creation tool

DTM_DrapeCloud converts 2D linework into usable 3D terrain geometry by keeping every XY position and calculating its Z elevation from nearby point-cloud points. This is the primary workflow for creating curbs, channels, ridges and other terrain breaklines directly from scan data.

You first draw or select the feature in plan. DTM_DrapeCloud then samples the point cloud along that geometry and updates its elevations. The resulting 3D polyline can be inspected, corrected and used as a constrained edge in a TIN.

Video placeholderCreate a curb breakline with DTM_DrapeCloudShow the original 2D polyline, mode selection and resulting 3D line over the cloud.

Prepare the linework in plan

  • Trace the real feature accurately in XY before assigning elevations.
  • Use polylines or splines for continuous terrain edges; points and blocks are also supported.
  • Keep separate lines for features with distinct elevations, such as the top and bottom of a curb.
  • Avoid unnecessary vertices, overlapping segments and self-intersections.
  • Add enough vertices to represent changes in direction and grade. DTM_DrapeCloud can also add samples along long segments according to the configured maximum segment length.
Image placeholderTop and bottom curb lines prepared in planShow separate 2D polylines over the point cloud before draping.

Drape linework onto the point cloud

  1. Run DTM_DrapeCloud from the DTM Tools ribbon or command line.
  2. Select the polylines, splines, points or blocks that need point-cloud elevations.
  3. Press Enter and choose the surface sampling mode.
  4. Use the configured sample radius. A smaller radius follows local detail; a larger radius creates a smoother and more stable result.
  5. Review the output. XY remains unchanged while the Z values are updated to follow the sampled cloud.

Choose the correct sampling mode

  • Bottom: uses the lowest point in the search radius. Useful for ground features when low returns are reliable.
  • Modal Band: finds the dominant elevation band and is generally the best choice for real street and terrain scans containing cars, vegetation or canopy.
  • Centroid: averages the local points. It provides broad coverage but can be influenced by mixed surfaces and noise.
  • Median or Mean: statistical alternatives for datasets where their behaviour is appropriate.
  • Max: follows the highest local points and is normally used only for a specific upper surface.

Recommended starting point: use Modal Band for most real-world terrain scans. It is more resistant to cars, vegetation and scattered outliers than a simple average.

Image placeholderBottom, Modal Band and Centroid results on the same curbUse a profile comparison that makes outlier handling visible.

Project linework onto an existing TIN with DrapeSurface

Use DTM_DrapeSurface when you already trust the finished terrain surface and want new breaklines, survey marks, splines or blocks to follow that triangulation exactly. Instead of sampling raw point-cloud points, the command reads elevations from the TIN itself.

  1. Run DTM_DrapeSurface.
  2. Select the polylines, splines, points or blocks that should follow the existing surface.
  3. Press Enter and then select the TIN, or press Enter again to let DTM Tools auto-detect a surface on the standard TIN layers.
  4. DTM Tools samples each vertex from the triangles using surface interpolation and adds vertices wherever the geometry crosses triangle edges.
  5. Review the result. The output now follows the current triangle mesh exactly, which is useful for edges that must stay consistent with the approved terrain model.

When to choose it: use DTM_DrapeCloud while building the first breaklines from raw scan data; switch to DTM_DrapeSurface when the TIN is already established and new geometry must inherit that exact surface.

Video placeholderDrape a new line onto an approved TIN with DTM_DrapeSurfaceShow TIN selection, automatic densification along triangle edges and the resulting 3D line.

Edit the breakline with Adjust Z

Drape creates elevations automatically, but individual vertices may still need correction where the scan is sparse, obstructed or contains the wrong local return. Use DTM_ADJUST_Z to edit those points in a dedicated profile view.

  1. Run DTM_ADJUST_Z.
  2. Select the draped 3D polyline.
  3. Open the profile view showing the polyline in the XZ plane.
  4. Use the colour-coded guides to compare each vertex with its neighbours.
  5. Drag a grip vertically to change that vertex elevation. The line updates in the drawing in real time.
  6. Close the profile view when the breakline follows the intended terrain feature.
Video placeholderCorrect draped breakline vertices with Adjust ZShow one scan spike and one missing return being corrected in the profile view.

Breakline quality checks

  • Inspect the line in plan, profile and isometric views.
  • Remove sudden elevation spikes caused by vehicles, vegetation or mixed scan layers.
  • Confirm neighbouring breaklines do not cross at contradictory elevations.
  • Check that curb tops, curb bottoms and channel lines remain separate where required.
  • Keep enough vertices to describe the grade without reproducing point-cloud noise.
Create a structured terrain modelUse the corrected 3D lines and gridded points in a constrained surface Check DTM qualityCompare the finished terrain with the source point cloud