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The Disc node creates a flat disc or circle, with or without a hole in the middle, suitable for surface displacements. It is a polygonal object, not a procedural one, and as such can also be used to create polygonal shapes like hexagons and triangles.

In Terragen, 3d objects fall into one of two categories; “Displaceable” or “Populatable”.

Displaceable objects rely on micropoly displacement at render time, which adapts to distance, resolution, etc. Worldspace texture coordinates are used for displacement, making these types of objects ideal for building world environments. By using Transform shaders, colour and other shaders can also take advantage of the worldspace texture coordinates. Displaceable objects update within the 3D Preview in non-RTP mode. Examples of displaceable objects are the Cube, Disc, Lake, Octahedron, Plane, Planet and Sphere objects.

Populatable objects can be instanced via a Populator node. On object nodes with displacement features implemented they rely on per-vertex/Mesh displacement in object space prior to instancing. These objects cast very precise shadow, reflections and subsurface scattering. They render faster, especially with reflections or in the Path Tracer, and have better motion blur and depth of field due to ray tracing. While these objects can also update within the 3D Preview in non-RTP mode, ideally the RTP mode is better suited for populatable and ray traceable items. Note that populations may need an extra repopulation step. Examples of populateable objects are the Card, Grass Clump, Poly Cube, Poly Sphere, Rock, and imported geometry in TGO/OBJ/LWO formats.

If you find that after making changes to the Octahedron’s settings, the 3D Preview or renderer does not seem to update and reflect those changes, select the Octahedron node and disable it by pressing “D” on your keyboard, then enable it again by pressing “D”.


  • Name: This setting allows you to apply a descriptive name to the node, which can be helpful when using multiple Disc nodes in a project.

  • Enable: When checked, the node is active and the Disc object will appear in the scene with the settings below applied to its surface. When unchecked, the node is ignored.

  • Show b-box in preview: When checked, the bounding box of the disc shape will be displayed in 3D Preview.
    Show bounding box in preview on and off

  • Render: An object's render state can be set to Visible, Invisible or Holdout. When set to Holdout, an object is visible in the rendered image as a black shape with an alpha value of zero. When using render layers the object's render state is combined with the group visibility parameter to determine its least visible setting. Invisible is less visible than Holdout, which is less visible than Visible.
    Render options

    Example of Render modes

  • Visible to other rays: When enabled, the Disc object will be taken into account by all the rays determined by the renderer including those from the camera, direct and indirect lighting, etc. In the example below, a 100% reflective 3D object has been placed behind three coloured spheres in order to mirror the effect of the calculated rays.
    Visible to other rays comparison

  • Cast shadow:When checked, the Disc object will cast shadows.
    Cast Shadows comparison

  • Render method: This popup has three options.
    Render method options

    Default: Ray Tracing is the default rendering method for an object. Typically it results in higher quality and faster rendering. When displacement is applied to a 3D object the render method should be changed to Force Displacement. When the object's render method is set to Default, the object is rendered according to the Ray trace objects setting in the render node.

    Force Displacement: When enabled for the Disc object, its surfaces will be subdivided into micropolygons at render time, which allows the 3D geometry to be displaced correctly but at the expense of slightly longer render times. It is useful when you have some objects you want to render with displacement but you don't want to change how all the rest of your objects are rendered, i.e. Ray traced.

    Force Ray Trace: When enabled for the Disc object, its surfaces will be ray traced at render time, even if Ray trace objects is disabled in the Renderer settings. This can be useful when Ray trace objects is disabled in the Renderer in order for other 3D objects to use displacement, but you want this object to use ray tracing for the highest quality rendering and it has not been displaced.

  • Sorting bias (metres): This setting gives you control over the order in which objects are rendered when using the micropolygon renderer. This does not apply to objects being rendered with the ray tracer. A large positive value, e.g. 10,000,000 (or 1e7) will usually force the object to render first. A large negative value, e.g. -10,000,000 (or -1e7) will usually force the object to render last, or after the terrain. This can be useful when rendering large objects with displacement, such as a lake object that lies mostly below the displaced terrain. By setting the lake object’s Sorting bias (metres) value to something like -10,000,000 forces it to render after the terrain.

  • Double sided surface: When checked, the shader or function nodes assigned under the Surface Shaders Tab apply to both sides of the Disc object. When unchecked, only the surface facing the positive axis direction is visible, therefore when viewing the Disc from behind, below, or from the negative axis, it would appear invisible.
    Double sided surface off and on

Transform Tab[edit]

Transform Tab

  • Center: This setting positions the Disc in the 3D scene.

  • Axis: This setting controls the orientation and up direction of the Disc.
    The Axis controls the orientation of the Disc.

  • Radius: This setting controls the outside radius of the Disc in metres.
    The Radius setting determine how large the Disc is.

  • Inner radius: This setting controls the inner radius for the Disc in metres. If you think of the disc as a donut, this is the radius of the donut 'hole'.
    The Inner radius setting determines if the Disc has a hole in it.

  • Divisions: This setting controls the number of polygonal slices that make up the Disc. The greater the number of slices the smoother the edge of the disc and more circular it appears. Other polygonal shapes can be created by using other values, for example a value of 6 will create a hexagon shape.
    Increasing the number of Divisions resutles in a smoother and more circular shape.

Surface Shaders Tab[edit]

Surface Shaders Tab

This tab lets you assign a surface shader to texture the Disc object.

  • Surface shader: Use this setting to assign a surface shader or function nodes to the Disc object.
    Various Surface shader with displacments.

  • Displacement tolerance: If you find that rough or spikey surfaces are showing problems at bucket edges, for example spikes having cut off tops, or gaps in ray traced shadows then increasing this value may help. However this can greatly increase render times. Relatively flat surfaces may render more quickly with smaller values. The default value is 1. However this is an advanced setting and you should not change it unless you have a specific problem you need to address. If you are having problems try starting with 2 and then increase it by small increments until they're resolved. A value of 4 would be considered a high value.

Literally, to change the position of something. In graphics terminology to displace a surface is to modify its geometric (3D) structure using reference data of some kind. For example, a grayscale image might be taken as input, with black areas indicating no displacement of the surface, and white indicating maximum displacement. In Terragen 2 displacement is used to create all terrain by taking heightfield or procedural data as input and using it to displace the normally flat sphere of the planet.

A single object or device in the node network which generates or modifies data and may accept input data or create output data or both, depending on its function. Nodes usually have their own settings which control the data they create or how they modify data passing through them. Nodes are connected together in a network to perform work in a network-based user interface. In Terragen 2 nodes are connected together to describe a scene.

The bounding box is a box which surrounds (or bounds) an object or shader. This box shows the maximum extents of the item inside it. Sometimes abbreviated as "b-box".

A parameter is an individual setting in a node parameter view which controls some aspect of the node.

A shader is a program or set of instructions used in 3D computer graphics to determine the final surface properties of an object or image. This can include arbitrarily complex descriptions of light absorption and diffusion, texture mapping, reflection and refraction, shadowing, surface displacement and post-processing effects. In Terragen 2 shaders are used to construct and modify almost every element of a scene.

When Terragen renders, it divides the image up into buckets or tiles. Each bucket is rendered separately, allowing multiple buckets to be rendered at once. It also allows memory to be used more efficiently.