Surfaces and terrain
A surface is a 3D model of the ground built from points and lines. It’s the base for every design, so learn to build it correctly and check it.
In this lesson you will
- Build a TIN surface from points
- Add breaklines and boundaries
- Display contours and analyse slopes and elevations
- Edit and check a surface
TIN surfaces
Civil 3D joins points into a triangulated irregular network (TIN). Every triangle is a flat plane; contours are interpolated across the triangles. The surface is only as good as its data and how the triangles connect.
Creating a surface
- 1Home › Surfaces › Create Surface: TIN surface, name EG (existing ground), style showing contours.
- 2In Prospector, expand the surface › Definition › Point Groups › Add the ground-shots group.
- 3Add breaklines from 3D polylines or feature lines along kerbs, ridges, toes of banks — they force triangle edges along real features.
- 4Add an outer boundary so triangles don't stretch across areas with no data.
- 5Rebuild if the surface shows as out of date.
Contours and analysis
Set contour intervals in the surface style (e.g. minor 0.5 m, major 2.5 m) and label them with contour labels.
Use surface analysis to shade elevation bands, slopes (e.g. anything steeper than 1:4 in red), slope arrows, and watersheds — essential for drainage and early earthworks thinking. Add an analysis legend table.
Editing and checking
Switch the style to show triangles and look for long skinny triangles and spikes. Edits such as Delete Line, Swap Edge and Add Line are recorded in the definition and can be undone individually. Prefer fixing the data (breaklines, boundaries, bad points) over manual edits.
Quick reference
| Command / tool | How to start it | What it does |
|---|---|---|
| Create Surface | Home › Surfaces | New TIN surface |
| Breaklines | Surface Definition | Controls triangulation along features |
| Boundaries | Surface Definition | Limits the surface extent |
| Surface Analysis | Surface Properties › Analysis | Elevation/slope/watershed shading |
Common mistakes
Contours cross a road kerb unrealistically.
Add breaklines along the kerb and edge of pavement.
Surface covers a huge area with long triangles.
Add an outer boundary or maximum triangle length.
Exercise
An existing ground surface
- Create EG from your ground-shot point group.
- Add a boundary and a breakline along a kerb.
- Show 0.5/2.5 m contours with labels.
- Shade slopes over 1:4 and add a legend.
- Inspect triangles and fix one bad point.
You should end up with: A checked existing ground surface.
Checklist
0 of 5 checked · saved on this device
Lesson quiz
What does TIN stand for?
Finished this lesson?
Taking the quiz marks it complete too. Your course page picks up where you stopped.
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