Quick answer
Run 
DTM_GroundExtract, select the scan area and choose a grid step. DTM Tools samples low points in the grid, reduces common above-ground clutter and creates a triangulated ground surface as native AutoCAD 3DFACE entities.
This result is an automatic, unstructured terrain model. It does not contain breakline information, so sharp curbs, channels, retaining edges and other strict terrain shapes are not explicitly enforced in the triangles.
Use it when you need broad terrain, not strict structure
Automatic ground extraction is most useful when the ground is irregular, natural or gently varying and you mainly need a terrain surface as a sampled grid of points. It is a strong first pass for embankments, open sites, excavations, general topography and other areas where there are no critical sharp edges to preserve exactly.
- Good fit: irregular ground, rough grading studies, first-pass terrain review, quantity checks and areas without strict geometric edges.
- Not the final workflow for: curbs, ditches, channels, walls, ridge lines, road edges and any terrain with sharp breaks in slope.
- Why: the automatic surface is driven by sampled points, not by surveyed breaklines that force specific triangle edges.
Extract the ground surface
- Attach the point cloud and run
DTM_GroundExtract. - Press Enter for the full cloud extent, select closed polygons, or draw a new boundary around the working area.
- Choose the sampling grid step. Smaller values retain more local detail; larger values produce fewer triangles.
- Inspect the output on layer
DTM-Ground-TIN.
Choose a useful grid step
The grid step controls the spacing of sampled terrain points. A value around 0.25-1.0 drawing units is a useful starting range when the drawing uses metres, but the correct value depends on point density, site size and the smallest terrain feature that must be retained.
- Smaller step: more detail, more triangles and more sensitivity to scan noise.
- Larger step: faster processing and a smoother, lighter surface.
- Critical edges: use breaklines in the structured terrain workflow rather than relying only on a very dense grid.
Use the structured terrain workflow when edges matter
If you need a terrain model with sharp angles, steep slope changes or clearly defined man-made features, switch to the second workflow: create a structured terrain model with breaklines. That workflow uses regular point samples plus breaklines to control the surface much more precisely in critical areas.
Recommended workflow split: use automatic ground extraction for a fast unstructured surface; use the structured terrain model guide when curbs, channels, retaining edges, road crowns or ridge lines must be represented explicitly.
Verify the model against the scan
Run 
DTM_DeviationMap to compare the TIN with the point cloud. Set a noise threshold to ignore distant outliers and a grid resolution for the heatmap. Red indicates cloud points above the model, blue indicates points below it, and green indicates close agreement.