Modeling terrain and organic shapes

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SketchUp implements the concept of a sandbox which refers to a surface that can be generated and manipulated using sandbox tools. A sandbox in SketchUp (and in other 3D modeling tools) is commonly referred to as a triangulated irregular network or TIN in terrain Modeling terminology. The following image shows a TIN (sandbox) in SketchUp.

Note: This documentation uses the term TIN, sandbox, and terrain interchangeably. A TIN is like a sandbox because it has a boundary and contains a sculpted surface (sand). Sandbox tools are those tools that are included in SketchUp for creating and manipulating TINs.

The following image shows a TIN in SketchUp with hidden geometry displayed (so you can see the triangles that are the foundation of the TIN).

There is nothing special about a TIN, it is simply several connected triangular faces that, when smoothed, appear like one continuos smooth surface. Note that you are not limited to creating terrain with the sandbox tools, you can create other organic shapes (shapes that appear to be crafted by hand) using these tools. For example, you might create a person's face, a bowl, or a swimming pool using the sandbox tools.

Another type of TIN-like surface, which the sandbox tools can work with, is called a polygon mesh. A polygon mesh is similar to a TIN, but contains faces with more than three vertices.

Note: SketchUp's Sandbox From Scratch tool and Sandbox From Contours tool only create TINs, but you can import a polygon mesh or create a polygon mesh (manually) using other SketchUp tools.


Triangles in a TIN can be oriented in different directions. The orientation of triangles is referred to as triangulation. Notice in the previous image that some triangles are oriented vertically while others are oriented horizontally. This concept is important because some sandbox tools allow you to change the direction of the triangles as a way to further smooth TINs.

Creating a TIN

There are several ways to obtain a starting TIN as the foundation of your model. These are:

  • Create or import contour lines and use the Sandbox From Contours tool to create a TIN.
  • Import an image of a site plan or contour map and trace its contours with the Freehand tool. Then, adjust the contours to their proper elevation and use the Sandbox From Contours tool to create a TIN.
  • Import a TIN using the SketchUp ArcGIS Plug-in available on the SketchUp Plugins page. ArcGIS is an industry standard application suite or Geographic Information System for working with geographical information such as the location of buildings within a world-wide global coordinate system.
  • Import a digital terraIn Model (DTM) file.
  • Create sandbox (TIN) using the Sandbox From Scratch tool.

Modifying a TIN

SketchUp contains several tools for modifying TINs. The following table lists all of the sandbox tools in SketchUp.




Sandbox From Scratch

Create TIN

Creates a flat, rectangular shaped, TIN or sandbox that can be modified by other sandbox tools.

Sandbox From Contours

Create TIN

Creates TIN or a sandbox from contour lines at various elevations.


Large Modifications

Allows you sculpt or make large modifications to a TIN by moving groupings of vertices to create hills, berms, or other features.


Large Modifications

Allows you to sculpt or make large modifications to a TIN by stamping footprints into the TIN, such as the footprint of a building.


Large Modifications

Allows you to drape the outlines of roads, paths and buildings, drawn on a flat plane, onto a TIN.

Add Detail

Small, Detailed, Modifications

Allows you to sculpt or make small, detailed, modifications to the a TIN by adding additional triangles to a TIN.

Flip Edge

Small, Detailed, Modifications

Allows you to sculpt or make small, detailed, modifications to the TIN by adjusting the triangulation of a TIN.

Note: The sandbox tools can also be used to create organic geometry or geometry that appears to be hand-crafted.

Functional terrain

The term functional terrain is used to describe terrain that has no portion bending back upon itself creating overhangs, underhangs, or caves. If you draw a vertical line through your terrain at any point and the line only touches the terrain at one point, your terrain is functional.

This concept is important because certain tools, such as the Smoove tool, can create unexpected results when working on nonfunctional terrain (the neighboring points included in the sculpting operation by the Smoove tool are often undesirable)..

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