2.7 Terrain Reference Surface

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Available for the Following Roles: All Roles

A Terrain Reference Surface is a surface that can be created in cmBuilder and used as a reference as an alternative to the the map's initial terrain for Earthwork Cut/Fill to surface operations. It allows for cuts/fills to create topographies that are more complex and appear more natural. Terrain Reference Surfaces are designed to be used when earthwork operations must follow a specific design surfaces.

In this article we cover:

• Create a Terrain Reference Surface

• Using Reference Surfaces for earthwork operation

Create a Terrain Reference Surface

1. Start by launching the Terrain Reference Surface tool:
   • From the toolbar, click Terrain (1) and select Terrain Reference Surface (2).
   • Alternatively, locate Terrain Reference Surface in the Scenario Tree and click the + button (3).
   • Select Surface from Points (4) from the side sheet

2. Next, add points, these will be used to generate the surface. A point can be placed on any object in the 3D space, and later repositioned using its' move handles or by editing its' coordinates. The side sheet point list will populate as points are added. Strategies to create project specific surfaces include: 
   • Add points on the underside of BIM Model foundation elements for use as a bulk excavation reference.
   • Add points on the underside of BIM Model SOG elements for use as back fill reference.
   • Import and position a civil surface model to drop points on top of, to locally cut/fill to.
   • Import and position a civil drawing to help with dropping points on the map then adjust their Z values.
     • Toggle on Use last selected point's elevation (1) to maintain the same elevation when adding new points, instead of adjusting each one individually after placing. 

💡Note: You can import point data uploading a CSV file (2), using either local or geo-coordinates (3). It is recommended to first download the template (4) and populate for import. CSV export is also available (5).

3. After at least one point is placed, additional options will become available, including:
   • Ability to Generate Preview (6) to preview the surface. 
   • Ability to move points, select a point from the list or 3D; move handles will appear on the point in 3D:
     • In 3D click and hold on a move handle (7) X/Y/Z arrow, drag your mouse to along the X/Y/Z axis.
     • From the list, click the 3 dots next to a point (8), select Edit X/Y/Z, type in a new value, then hit enter.
   • Ability to delete points, select a point from the list or 3D:
     • From the list, click the 3 dots next to the point, select Delete (9).
   • Hit Confirm when all points are placed to generate the surface -these can be edited later if needed.

4. The surface will be listed in the Scenario tree under the Terrain Reference Surface section -it will be hidden by default. Right click on the surface (1) to view options like Edit, Temporary Hide/Show, Delete and more. In the example below the surface (2) is Temporarily Shown for visualization/validation purposes. 

Using Reference Surfaces for Earthwork Operations

1. Start by creating an Earthwork cut or fill operation:
   • From the Toolbar and click Terrain (1), then select Earthwork (2).
   • From the Side Sheet on the right, select either a Cut or Fill earthwork operation (3).

2. Create the excavation operation boundary sketch:
   • Click in 3D to set the sketch elevation. This will be the top elevation for a Cut, or bottom for a Fill.
   • Sketch the area you want to cut in the Scenario and click Confirm (4).

3. Modify the cut/fill operation's settings as needed:
   • (Required) choose Cut (or Fill) to Surface (5).
   • From the Surface dropdown and select your Terrain Reference Surface (6).
   • (Optional) set an Offset (7) value
     • Positive values limit the cut to above the surface, while negative values limit the cut to below it.
   • Click Done (8) to apply the settings.

The Earthwork Cut will now align with the selected Terrain Reference Surface.

Common Use Cases

Adjust Google Maps Topography

When the Google Maps topography does not accurately represent the site, use points to trace the existing terrain and create a Terrain Reference Surface. You can then apply a single Site Condition across the area and cut the terrain to the reference surface instead of processing the same area multiple times. After creating the cut, apply the Map texture to help the modified terrain blend with the surrounding satellite imagery.

Recreate Excavations from an Existing Model

Use an imported model as a reference when recreating existing excavations such as ramps, slabs, or retaining walls. Place points along the relevant geometry to create a Terrain Reference Surface, then use the surface as the target for cutting or filling the terrain. If multiple cuts use the same reference surface, duplicate an existing cut and reuse the surface instead of tracing the geometry again.

Create Custom Cuts and Fills with Sloped Geometry

Create more complex excavations and fills by placing points at different elevations to define the required shape. A Terrain Reference Surface can include a sloped bottom, sloped walls, or both, allowing you to model stockpiles, irregular excavations, and curved ramps. The resulting terrain can then be used for more accurate quantity takeoffs and truck animations.

Create Curved Ramps

Create a Terrain Reference Surface that follows the intended shape and elevation of a curved ramp, then use it as the reference for a cut or fill. By defining points along the ramp at different elevations, you can create curved and customized ramp geometries. This also allows the ramp to be included in quantity takeoffs and truck animations, which may not work correctly when using a library resource alone.

Build Soil Profiles from Borehole Data

Use borehole data to create multiple terrain reference surfaces representing different soil layers. Start by creating a surface for the first layer, export its point data as a CSV, and reuse the points for subsequent layers by adjusting the elevations. This allows you to build separate reference surfaces for each soil layer and use them to represent the site's subsurface conditions.

Reference Water Levels

Use a Terrain Reference Surface to represent a water level alongside soil profiles or other site conditions. This provides a visual reference for understanding how the water level relates to planned cuts and other earthwork operations.

Video Tutorial

Watch the workshop video below to see these use cases demonstrated in practice