How to Create a TIN Surface in BricsCAD

Quick answer: TIN creates a Triangulated Irregular Network surface from points, breaklines, and boundaries, generated from drawing entities, point files, point clouds, 3D faces, or imported Civil 3D surfaces. Used in BIM models to represent a site.

What a TIN Surface Is Built From

• Points: X, Y coordinates plus a Z value. Every point connects to its two nearest neighbours to form triangles, using the Delaunay algorithm, which guarantees no point sits inside any triangle’s circumcircle.
• Breaklines: represent linear infrastructure like curbs or retaining walls, and define triangle edges directly. Created from lines, polylines, arcs, or circles.
• Boundaries: define a bounded 3D surface, built from closed polylines. Defining outer boundaries on a large surface improves performance.

TIN surfaces can be generated from point clouds, drawing entities, 3D faces, custom ASCII point files, or Civil 3D surfaces.

TIN Surface Preferences

• Arc approximation mid-ordinate distance: the maximum distance allowed between an arc and its straight chord when tessellating curved polylines into the surface. Defaults vary by template: 0.01 in BIM-m, 1 in BIM-cm, 10 in BIM-mm, and 0.4 in BIM imperial.
• Allow breakline crossings: on by default. When allowed, intersections between breakline segments are calculated and added as points.
• Elevation at breakline crossings: minimal, maximal, or average, for determining elevation at those intersections.
• Associativity: enables or disables associativity between TIN surfaces, gradings, TIN volume surfaces, and corridors, stored as a bitcode defaulting to 15 (everything enabled):

Properties of a TIN Surface

• TIN Visibility: toggles for Boundary line, Points, Triangles, and Contours, plus major/minor contour interval and colour.
• TIN Analysis: Elevations and Slopes toggles, each with an Edit… option opening a dedicated dialog to define the analysis parameters.
• TIN Statistics: number of points, number of triangles, minimum and maximum elevation, and 2D and 3D area.

Creating a TIN Surface

From drawing entities:

1. Open a drawing with CAD points, blocks, and polylines.
2. Launch TIN.
3. Select all the entities.
4. Press Enter.
5. Choose whether to apply selected linear entities as breaklines.

A TIN surface keeps a live connection to linear entities added as breaklines, editing them rebuilds the surface automatically. This connection isn’t maintained if entities are added as edges or points instead, or for blocks and points generally.

From a point file:

1. Launch TIN and choose Import from file.
2. In the Create Surface From Point File dialog, select one or multiple point data files.
3. Choose the point file format from the dropdown (the browse button manages available formats).
4. Optionally toggle Applicable formats only to filter to formats matching your selected files.
5. Click OK.
6. Choose No to create the surface without simplifying points first.

From a point file using a clip polygon:

1. Use or create a closed polyline defining the area you want.
2. Launch TIN and choose cLip polygon.
3. Select the closed polyline as your clipping boundary.
4. Choose Import from file (other options are also available here: select drawing entities, create from Faces, from Point Cloud, or from Point Groups).
5. Follow the point file procedure above.

The algorithm connects triangles outside a concave clip polygon’s boundary, creating long, narrow triangles. Remove these with TINEDIT‘s Remove Outer Edges option, specifying the maximum triangle length to remove.

By placing points:

1. Open a drawing and launch TIN.
2. Choose place Points.
3. Pick a point, specify its elevation, and press Enter to accept; repeat for each point. At least three points are needed.

From 3D Faces:

1. Open a drawing containing 3D faces and launch TIN.
2. Choose create from Faces.
3. Select the faces you want.
4. Choose whether to apply the faces as edges. If yes, the faces’ edges and vertices are used, so the surface follows their edges. If no, only vertices are used, and the surface won’t follow the face edges.

From a Point Cloud:

1. Open a drawing containing a point cloud and launch TIN.
2. Choose create from point Cloud.
3. Select the point cloud and press Enter.
4. Choose No to skip simplification.

Using TIN Simplify and TIN Densify with a Point Cloud: follow the Point Cloud steps above, then:

1. Choose Yes to simplify.
2. Enter a radius for the simplification step.
3. Enter an elevation difference.
4. Choose Create tin surface, or Simplify again to adjust the parameters (the Command line reports point counts before and after simplification to help you decide).
5. Choose Yes to densify, or No to keep the simplified surface as is.
6. Enter an elevation difference for densification.
7. Choose the area to densify: existing polygons, a newly drawn polygon, or press Enter to use the entire surface.

Densification returns individual points within the specified area, ensuring the elevation difference between the original and final surface never exceeds your specified value there. You can edit these Simplify and Densify parameters anytime in Civil Explorer, right-click the surface’s Add points definition and choose Edit.

From a Civil 3D surface:

1. Open a drawing containing a Civil 3D surface and launch CIVIL3DIMPORT.
2. In the Import Civil 3D dialog, choose Convert from current drawing.
3. Select the Civil 3D surfaces to convert (Point Groups, Alignments, and Profiles can also be converted here).
4. Specify a name template for the imported objects.
5. Tick Import Civil 3D labels as blocks.
6. Click OK.

Assigning an Image to a TIN Surface

1. Open a drawing containing a TIN surface and an image, and launch TINASSIGNIMAGE.
2. Select the TIN surface.
3. Select the raster image.

If the image doesn’t appear, switch the Visual Style to Modeling or Realistic and make sure TIN surface triangles are on.

Projecting Entities onto a TIN Surface

1. Open a drawing containing a TIN surface and the entities you want to project (points, blocks, text, lines, polylines, or circles), and launch TINPROJECT.
2. Select the entities to project.
3. Choose whether to erase the original entities.

Frequently Asked Questions

Does editing a breakline always update the TIN surface automatically? Only if that linear entity was added as a breakline specifically. Entities added as edges or points, or blocks and points generally, don’t maintain that live connection.

How many points do I need at minimum to create a TIN surface by placing points manually? At least three.

What’s the difference between applying 3D Faces as edges or not when creating a TIN surface from them? Applying them as edges uses both the faces’ edges and vertices, so the surface follows those edges. Not applying them uses only the vertices, so the surface doesn’t follow the original face edges.

Why would I use TIN Simplify and Densify together on a point cloud? Simplify reduces an enormous point count to something manageable; Densify then selectively restores detail in specific areas where accuracy matters, keeping the elevation difference from the original within a value you set.