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DifficultybeginnerAdded2027.0Statusdraft

Surfaces (DTM) (Civil 3D essentials)

Terms and Definition​

A surface is a singular object in Autodesk Civil 3D. The surface style controls how the surface displays. Surface styles can be used to display the surface as points, triangles, borders, contours and grids. Usually, several surface styles are available in an Autodesk Civil 3D drawing. Each surface style serves a different purpose.

The following key terms relate to Surfaces:

DTM Digital Terrain Model. Different name for a surface.

TIN Triangulated Irregular Network. Autodesk Civil 3D uses a TIN to represent surface models. A TIN is created by connecting the points with closest proximity.

Breaklines Breaklines represent distinct terrain breaks. Examples of breaklines include road crowns, gutters, top of bank, bottom of bank, ditch edges, stream edges and sidewalk edges. When creating Surfaces, breaklines should be defined. Triangulation lines are forced to "break" the terrain and run over the length of defined breaklines. Triangulation lines cannot cross over breaklines.

Proximity A proximity breakline is defined from 2D polylines. Proximity breaklines assign

Breaklines vertex elevations by physically relocating them to the nearest surface point. 2D polylines created with vertices at the point nodes do not relocate.

Contour A contour line connects Points on the surface with constant elevation. Contour lines are created by connecting locations on triangulation lines with the same elevation.

Surface The surface style controls the display of the surface. Surface styles can be used

Style to display Surfaces as triangles, points, contours, borders or grids. You can also create surface styles to suppress the display of a surface, this is useful when working with large Surfaces.

Naming Naming templates are used in Autodesk Civil 3D to automatically assign names to newly created objects. Naming templates are useful when large amounts of civil engineering data are being created, it helps to organise the data in the drawing. Users can override the automatically assigned names with naming templates.

Invalid Invalid DTM Points are excluded from the point groups used to create surface

DTM Points models. These Points do not represent true surface elevations. Typical examples include sewer inverts and tops of fire hydrants.

Create Surface from Point File​

  1. Create a new surface by going to Home – Surfaces in the ribbon and selecting the Create Surface command**:**

  2. For the Type select TIN surface, specify a Name and Style:

  3. Go to Toolspace − Prospector –Surfaces – NGL (name of the surface created in the previous step) – Definition, right-click on the Point Files and select Add from the menu:

  4. Browse for the point file by clicking on the Plus icon and specify the correct file format. The file format must match the point file's format. The Preview helps to ensure that the correct file format is selected:

The image below shows the created surface (only the surface border is displayed):

Create Surface from Contours​

  1. Create a new surface by going to Home − Surfaces in the ribbon and selecting the Create Surface command:

  2. For the Type use TIN surface, specify a Name and Style:

  3. Copy contours from the source drawing into the design drawing. Use the copy (CTRL+C) command and then the Paste to original coordinates command:

  4. Contours must be represented by lines or polylines that have elevations. Splines must be converted to polylines (the Republic of South Africa Reports Manager can be used for this purpose, see image below):

  5. To add contours to a surface, go to Toolspace − Prospector –Surfaces – NGL (name of the surface created in previous step) – Definition, right-click on Contours and select Add from the menu:

  6. Keep the default settings, click OK and select the contours in the drawing:

The image shows the surface that was created (only the border is displayed, visible contours are the source contours, they can be frozen but don't delete them because they will be removed from the surface definition):

Create Surface from 3D Faces​

  1. Create a new surface by going to Home − Surfaces in the ribbon and selecting the Create Surface command:

  2. For the Type use TIN surface, specify a Name and Style:

  3. Copy the 3D faces from the source drawing into the design drawing. Use the copy (CTRL+C) command and then the Paste to Original Coordinates command:

3D faces are AutoCAD objects, the method described can be used for other AutoCAD objects as well:

  1. Go to Toolspace − Prospector –Surfaces – NGL (name of the surface created previously) – Definition, right-click on Drawing Objects and select Add from the menu:

  2. Specify 3D Faces as an object type, tick Maintain edges from objects if you want the surface triangulation to match with the 3D faces. Click OK and select the 3D faces:

The image shows the created surface (only the border is displayed):

Create Surface from Model Maker TOT File​

Standard Civil 3D cannot import TOT files, if you have Devotech iDAS see the Import TOT chapter to create a surface from a TOT file.

Create Surface from Civil Designer DAT File​

Standard Civil 3D cannot import DAT files, if you have Devotech iDAS see the

Import CDM Command / Import ModelMaker CDM Command

Description:

Imports lines and/or COGO points from a ModelMaker CDM file. The lines or points can then be used to create a surface.

Location on Compact Ribbon:

Location on Extended Ribbon:

Instructions:

    1. Run the command.
    2. Select the CDM file from the file system.
    3. Choose the objects to import:

Import DAT chapter to create a surface from a DAT file.

Change Surface Style​

Surfaces can be displayed with multiple styles or even with no style. Even if the surface is not visible in model space, it is still part of the drawing and can be accessed from the prospector. Changing between different styles does not modify the surface definition.

  1. To change the surface style, right-click on the surface either in the model space or in the Prospector and select Surface Properties from the menu:

  2. In the Information tab select the surface style:

The image shows the contours surface style:

Add Breaklines to Surface​

Different breaklines can be added to a surface in Civil 3D. The following method shows how to add Standard breaklines. A standard breakline can be defined by 3D lines, grading feature lines, 3D polylines or splines, it can represent road edges, ditches, kerbs, channels and other edges.

  1. Copy breaklines from the source drawing into the design drawing. Use the copy (CTRL+C) command and then the Paste to Original Coordinates command:

The image shows the breaklines pasted into a drawing which contains a surface. The surface is displayed with triangles.

  1. Go to Toolspace − Prospector –Surfaces – NGL (name of the surface) – Definition, right-click on Breaklines and select Add from the menu:

  2. Select the Standard breakline Type, click OK and select the breaklines:

The image shows the surface with the added breaklines, the surface triangle edges honour the breaklines:

Add Surface Labels​

Various labels can be added to a Civil 3D surface. Labels are dynamic meaning that any changes to the surface will automatically be projected to the labels.

  1. To add surface labels, go to the ribbon Annotate – Add Labels and use the Add Surface Labels command**:**

Add Slope Labels​

  1. In the Add Labels window, select Slope as a label type, Percent as a slope label style and click Add:

  2. Specify whether to create a One-point or Two-point label and click on the surface. A one-point label displays the surface slope at the defined point, a two-point label calculates the slope between two defined points:

Add Spot Elevation Labels​

  1. In the Add Labels window, select Spot Elevation as a label type, as a spot elevation label style use Spot Elevation | Text Size 2.5 mm | Precision 0.01, as a marker style use Surface-Spot Elevation Point and click Add:

  2. Click on the surface at the location where you want the place the spot elevation label. The image below displays the spot elevation labels with a text style 2.5 mm (yellow) and 3.5 mm (green):

Add Multiple Contour Labels​

  1. In the Add Labels window select Contour – Multiple as a label type. Choose a major contour label style, minor contour label style, user contour label style and click Add:

  2. Specify points on the screen (the points are connected with a contour label line):

  3. To move the contour label location, click on the labels, snap on a contour label line grip and move it to the desired location:

Surface Analysis​

Elevation Analysis​

  1. Go to the Surface Properties (right-click on the surface in model space or in the prospector and select Surface Properties from the menu), in the Analysis tab**,** select Elevations as the Analysis type, specify the Number of ranges and click on the downwards pointing arrow to run the analysis:

  2. To display the analysis results, you must change the surface style to one which will display the elevation analysis. The style can be changed in the Information tab.

The image displays a surface with an elevation analysis:

Slope Analysis​

  1. Go to the Surface Properties (right-click on the surface in model space or in the Prospector and select Surface Properties from the menu), in the Analysis tab**,** select Slopes for the Analysis type, specify the Number of ranges and click on the downwards pointing arrow to run the analysis. You can define the min and max slope and the colours:

  2. To display the analysis results, you must change the surface style to one which will display the slope analysis. The style can be changed in the Information tab.

The image displays a surface with a slope analysis:

Watershed Analysis​

  1. Go to the Surface Properties (right-click on the surface in model space or in the Prospector and select the Surface Properties from the menu), in the Analysis tab**,** select Watersheds for the Analysis type and click on the downwards pointing arrow to run the analysis. You can specify the parameters to Merge adjacent boundary and Merge depression points into single drain:

  2. To display the analysis results, you must change the surface style to one which will display the watershed analysis. The style can be changed in the Information tab.

The image displays a surface with a watershed analysis:

Water Drop Analysis​

  1. In the ribbon, go to Analyze – Flow Path and select Water Drop from the menu:

  2. Click on the surface to create water drop analysis:

Catchment Area Analysis​

  1. Go to the ribbon Analyze – Catchments and select Catchment Area from the menu:

  2. Select a depression point on the surface. Keep in mind that not all the points on the surface have catchment areas.

Add Surface Outer Boundary​

  1. Draw a closed polyline that represents the surface boundary. In the Prospector under Surface, Definition, right-click on Boundaries and select Add from the menu:

  2. Select Outer as the boundary type, click OK and select the polyline:

The image shows a surface with a defined boundary:

Set Maximum Triangle Length​

The software sometimes creates triangles that are not supposed to be part of the surface. This might occur when a survey is done in two blocks apart from each other. Civil 3D automatically tries to connect these blocks with triangles, see the image below:

  1. To solve this problem, set the Maximum triangle length to a logical value in the Surface Properties – Definition – Build:

The image displays a surface with the maximum triangle length set to 100m:

Add Surface Table​

  1. In the ribbon go to Annotate – Add Tables and select Add Surface Legend Table from the menu:

  2. Specify the label type you want to create:

  3. Specify if you want the table to be static or dynamic:

  4. Specify a location for the table in the drawing area: