A BricsCAD Civil surface workflow starts with survey points or imported terrain data. If you want to know How to Create TIN Surfaces, Contours and Elevation Analysis in BricsCAD, this guide follows the full path from raw survey data to a checked terrain model BricsCAD teams can trust. It turns survey points to surface data into a clear terrain model BricsCAD users can review.
The same method helps with early site checks, civil design, earthworks review, and drawing control.
Before you create a BricsCAD TIN surface, check your licence level and your data. TIN surface, grading, and alignment creation requires BricsCAD Pro or higher, so none of this is available in BricsCAD Lite. Then make sure the data has good X, Y, and Z values.You also need to know what the surface should include and what it should leave out.
A TIN surface can come from CAD points and linear entities, Civil points, point groups, ASCII point files, 3D faces, point clouds, contours, and mesh or polyface mesh entities. Since V26 it can also be built from a DEM grid using TINFROMDEM, which reads GeoTIFF, USGS DEM, ESRI Arc/Info Binary Grid, and ESRI ASCII Grid files. Surfaces can also be imported from LandXML or converted from Civil 3D surfaces.
For a UK housing site, the survey may include spot levels, kerb lines, a top and bottom of bank, drainage covers, and a site boundary. The aim is to build a terrain model in BricsCAD that shows the ground, makes contours, and flags steep areas before road and floor levels are set.
Use this quick check list:
Start with the source data. A TIN surface is only as good as the data behind it. If the source is poor, you can get spikes, holes, flat spots, or triangles that reach too far.
Open the drawing with your CAD points, civil points, blocks, polylines, 3D faces, point cloud reference, or point file. Zoom over the full site. Look for bad outliers, like one point far above the rest. If point labels show levels, compare them with the Z values in Properties.
If the project uses a local benchmark or metres above ordnance datum, make sure everyone uses the same vertical base. That matters for elevation analysis CAD output and for later design checks.
A simple prep flow is:
If you import a point file, note the file type and column order. If geometry comes from another CAD tool, inspect it carefully. Imported points, blocks, and polylines may not behave as expected after translation.
Once the data is clean, create the surface from the objects you need. In BricsCAD, the TIN command builds a Triangulated Irregular Network from the source data you select. Triangulation uses the Delaunay method, which ensures no point sits inside the circumcircle of any triangle. Source data is not limited to points and line entities, as the command also accepts Civil points, point files, point groups, 3D faces, point clouds, contours, and mesh entities. When you create it from drawing objects, you select the source items and then choose how line entities should affect the surface.
Follow this workflow:
Do not style the surface right away. First, orbit the model or view it from an isometric angle. Look for steep spikes or deep pits. A strange triangle pattern often means a bad level, a missing breakline, or the wrong object in the set.
For the housing access road example, the first pass may show the overall fall from the rear of the site toward the road. But without boundaries and breaklines, triangles may cross the site entrance, smooth over a kerb, or bridge a ditch. That is normal for a first-pass BricsCAD TIN surface.
You can define the area the surface should cover either during creation or afterwards. The TIN command has a cLip polygon option that builds the surface only inside a selected closed polyline. If the surface already exists, add the boundary with TINEDIT. Boundaries are closed features that limit the surface extent. A closed polyline is usually used.
A boundary also helps performance. Bricsys documents that defining outer boundaries on a large surface improves the performance of a TIN Surface plan, because the display no longer has to carry outer triangles you do not need.
Use this process:
Boundaries do more than clean up the view, but they do not stop the triangulation itself. An Outer boundary hides the triangles beyond it, and trimming is off by default, so triangles crossing the boundary are deleted rather than trimmed unless you set Trim triangle lines to Yes. Long, thin triangles can still appear, particularly around a concave clip polygon. Clear them with the Remove Outer Edges option in TINEDIT, which removes boundary triangles by maximum edge length, minimum edge length, or maximum adjacent angle.
On the UK site, the boundary may follow the rear garden line, the highway edge, and the side wall, not just a simple box.
If the surface clips the wrong area, check that the polyline is closed, in the right place, and on the right surface. Also check that you did not pick an inner feature when you meant the full site edge.
Breaklines tell the TIN where the ground changes fast or must stay steady along a line. Without them, the mesh connects nearby points and may miss a kerb, ditch, ridge, wall, or top of bank.
BricsCAD treats breaklines as line features that shape triangle edges. They can come from lines, polylines, arcs, and circles. The Add Breaklines dialog offers two types. Standard rebuilds the surface so triangles follow the breakline edges and elevations. Projected drapes the breakline onto the surface and creates new triangles without changing elevations. The same dialog sets a mid-ordinate distance for approximating arcs, plus optional weeding factors, which drop vertices that sit too close together, and supplementing factors, which add vertices where spacing is too wide. Weeding and supplementing are disabled for Projected breaklines.
Common breaklines are:
Use this flow:
For the housing access example, the kerb at the road edge should often be a breakline. The top and bottom of the rear bank should also be breaklines. They help the BricsCAD TIN surface keep a realistic shape.
Breaklines can also expose bad survey data. If a kerb line makes a spike, one vertex may have the wrong level. If a ditch looks flat, the source polyline may be 2D. Fix the source data first, then update the breakline.
Once the TIN surface is clipped and controlled, turn on contours. Contours turn the triangle mesh into readable level lines. Many people find them easier to read than triangles.
In Civil Explorer and surface Properties, you can turn on contour display and set major and minor intervals and colours. These contours are a display property of the surface, not separate drawing entities. To produce contours you can plot, label, or hand to another package, run TINEXTRACT and tick Major contours and Minor contours, giving each an interval and a target layer. TINEXTRACT works on Gradings and TIN Volume Surfaces as well as TIN surfaces.
To create contours in BricsCAD, follow this flow:
Choose intervals that fit the site. A steep slope needs a different setting from a flat car park. Do not use very tight spacing just because the software can show it. If the survey is sparse, dense contours can suggest more detail than the data really has.
On the UK site, contours across the parking court can show if the ground falls to the road or to the neighbouring plots. If the lines pinch hard near the rear boundary, you may have a bank, wall, or steep step that needs attention.
Use contours as a check tool, not just an output. If a contour loops oddly, crosses a kerb in a strange way, or looks jagged in open ground, go back to the points and breaklines.
Elevation analysis adds colour bands to the surface. It helps you see high and low zones fast, compare design levels, and explain the site to people who do not work in CAD every day.
BricsCAD Civil Explorer includes elevation analysis tools for selected TIN surfaces and TIN Volume Surfaces. Ranges can be built three ways: by Number of ranges, by Range interval from a base elevation, or by Range interval with datum, which allows a separate colour scheme above and below the datum. Colour schemes are Spectrum, Earth, Hydro, Gray, Reds, Greens, Blues, and Custom. Display options are 3D Triangles, 3D Contours, Points, 2D Triangles, and 2D Contours. You can also set a minimum and maximum elevation with a separate colour for out of range values, and insert a legend into the drawing.
Use this flow:
For a UK housing site, elevation analysis may show that the rear gardens sit well above the access point. That does not give the answer by itself, but it shows where ramps, retaining walls, steps, or drainage changes may be needed. If you are preparing an early plan, this visual check can guide the talk before detailed vertical design starts.
Be careful with colour. A strong colour change does not always mean a problem. It may just mean the range settings are tight. Check the min and max levels before you draw a conclusion.
Reviewing elevation analysis first is a useful habit rather than a software requirement. Elevation and slope analysis are independent display settings, and either can be switched on without the other. Learning the height pattern first usually makes the slope bands easier to interpret.
BricsCAD slope analysis tools let you review slope bands on a selected TIN surface. Slope analysis is deliberately simpler than elevation analysis. It is offered for TIN surfaces only, not TIN Volume Surfaces, and the display options are limited to 3D Triangles or 2D Triangles. You set a colour scheme and a number of ranges, edit the slope values in the table, and insert a legend if needed. For written slope callouts rather than a colour map, use the Slope option in ADDSURFACELABELS, either from a single point or between two points.
Use this sequence:
On the UK site, slope analysis may show that the access route crosses a steeper area than expected. That is a prompt to review road grades, foot access, drainage falls, and tie-ins to nearby land.
Do not treat slope colours as a design rule. They are a visual aid. They help you find areas to check, but the final call still depends on the brief, local rules, and project standards.
A BricsCAD Civil surface is ready when the shape matches the survey intent, the boundary is under control, the breaklines keep key terrain features, and the contours and analysis views act as expected.
You do not need a complex model. You need one you can trust.
Before you issue screenshots or use the model for more work, do a final check:
If you later get new survey points or new terrain data, repeat the same order: update the source, rebuild or edit the TIN, check the boundary, review breaklines, regenerate contours, then rerun elevation and slope analysis. That keeps the terrain model BricsCAD teams use consistent and easy to fix.
Question: What data can be used to create a TIN surface in BricsCAD?
Short answer: You can use data with good X, Y, and Z values. That includes CAD points and linear entities, Civil points, point groups, custom ASCII point files, 3D faces, point clouds, contours, and mesh entities. You can also build from a DEM grid using TINFROMDEM, which supports GeoTIFF, USGS DEM, ESRI Arc/Info Binary Grid, and ESRI ASCII Grid, or import from LandXML, or convert a Civil 3D surface. Always check the levels first and remove non-terrain objects.
Question: Why should boundaries be added to a TIN surface?
Short answer: Boundaries control which triangles are displayed at the surface edge. An Outer boundary hides everything beyond it, and by default triangles crossing the boundary are deleted rather than trimmed. Boundaries do not prevent the triangulation from reaching past the survey area, so use the Remove Outer Edges option in TINEDIT to clear long, thin triangles. Defining an outer boundary on a large surface also improves performance.
Question: When should breaklines be used?
Short answer: Use breaklines where line features control the shape of the ground, such as kerbs, banks, ditches, retaining walls, road edges, channels, and thresholds. They help the surface keep sharp or steady grade changes instead of smoothing them out.
Question: How are contours different from elevation analysis?
Short answer: Contours show the surface as level lines, so the shape is easy to read in plan. Elevation analysis groups the surface into colour bands, so you can see high and low zones fast. The two overlap, because elevation analysis can itself be displayed as 2D or 3D contours rather than triangles. The practical difference is output: contours extracted with TINEXTRACT become real polylines you can plot and label, while elevation analysis remains a display property of the surface.
Question: Why should elevation analysis usually be reviewed before slope analysis?
Short answer: Elevation analysis shows the height pattern first. Once you know where the high and low areas are, slope analysis can show how fast the levels change. That makes steep zones, access limits, drainage issues, and retaining needs easier to read.
