Using Datasmith with Rhino

Describes special considerations that apply when you use Datasmith to import scenes from McNeel Rhinoceros 3D.

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This page describes how Datasmith imports scenes from McNeel Rhinoceros (Rhino) into Unreal Editor. It follows the basic process outlined in the Datasmith Overview and About the Datasmith Import Process, but adds some special translation behavior that is specific to Rhino. If you're planning to use Datasmith to import scenes from Rhino into Unreal Editor, reading this page can help you understand how your scene is translated, and how you can work with the results in Unreal Editor.

Rhino Workflow

Datasmith uses a Direct workflow for Rhino. That means that to get your Rhino content into Unreal using Datasmith, you simply need to save your Rhino scene to a .3dm file, and use the Datasmith CAD importer to bring that file into the Unreal Editor. See Importing Datasmith Content into Unreal Engine 4.

Converting Geometry into Static Meshes

Datasmith creates a separate Static Mesh Asset for each separate mesh, solid, or surface in the Rhino file. If the object has its Name property set in the Properties panel in Rhino (shown on the left in the image below), Datasmith uses that name for the Static Mesh Asset (shown on the right in the image below). Any Actors that Datasmith creates in your Level that refer to that Static Mesh Asset also use the same name.

Instancing

When Datasmith detects multiple instances of the same block in your Rhino scene, it only creates one set of Static Mesh Assets for the geometry in that block, and places multiple instances of those Static Meshes into the scene. This is typically better for the runtime memory requirements and performance of your Project, as well as making it easier to manage the number of Static Meshes in your Content Browser.

Wherever possible, we recommend taking advantage of this by making any repeating elements in your scene (such as windows, doors, or chairs) into blocks in Rhino. For details, see the Rhino documentation.

Tessellation and Render Meshes

Datasmith tessellates the surfaces of the objects in your Rhino scene into triangular meshes using the same process as it uses for other types of CAD files.

For details on this process, and the settings you can use to control how closely the final triangular mesh in the Unreal Engine matches the original surface in your source scene, see Using Datasmith with CAD FIle Formats.

Triangle Facing Direction

Rhino typically displays all surfaces as two-sided, regardless of the direction of their surface normals. However, the Unreal Engine automatically culls triangles that face away from the camera. This may cause some geometry in your scene to disappear when viewed from certain angles.

For example, the image below shows a wheel well cover that was modeled with its surface normals facing inward. After the scene is imported into Unreal, the sides at first appear to be missing. In this case, flipping the normal direction of the object makes the sides appear as they should.

backward-facing

forward-facing

For a complete discussion and recommended solutions, see About the Datasmith Import Process.

Rhino Materials

For each different surface color and material that Datasmith finds in your Rhino scene, it creates a separate Material Asset in Unreal, and places it in the Materials folder next to your Datasmith Scene Asset.

  • Unreal Materials that represent Rhino materials keep the names they have in Rhino. These Material Instances use the Datasmith_Material as their Parent. For details, see Rhino Material Properties below.

  • Unreal Materials that represent Rhino display colors have names automatically generated for them based on the values of the RGB channels. These Material Instances use the Datasmith_Color as their Parent Material. For details, see About the Datasmith Import Process.

Material and Color Assignment

In Rhino, the material or color used to draw an object's surface can be assigned to the object itself, to its layer, or to its parent, and may depend on the properties of the current viewport. However, in Unreal, each triangle that makes up the surface of a Static Mesh Asset needs a single Material to define its rendering properties. Datasmith therefore needs to interpret the surface display properties for each geometry object in Rhino to determine a single way for that object's surface to be rendered in Unreal.

To do this, it uses the following rules:

  • It first tries to find a material for each surface. It uses each object's Assign material by setting in Rhino to determine the source of the material that should be used to shade that surface.
    Assign material by

  • If that source does not have a material assigned to it, Datasmith falls back on using the Display Color property set for the object.
    Display Color
    That setting may in turn be defined directly on the object itself, or it may point to the object's layer or the object's parent block.

Rhino Material Properties

The goal of the Rhino Material conversion process is to take the settings you're familiar with from Rhino, and interpret them in a way that produces similar results with Unreal's physically based renderer.

As you can see from looking at the settings side-by-side, each Material Asset created by Datasmith offers the same Basic properties and the same Texture types that you can set in Rhino:

The only Rhino properties that are missing from the Datasmith Material are the ambient color and diffuse color settings:

  • In Unreal, you can take care of adding extra ambient lighting when you set up lighting for your Level, not in individual Materials.

  • You can simulate the effect of unchecking Rhino's Enable Diffuse Lighting checkbox by changing your Unreal Material's General > Material Property Override > Shading Model** setting to Unlit.

Note: If your Rhino material uses a texture with a blend percentage, the percentage value is not automatically carried over into the Unreal Material. However, you can set it in Unreal using the corresponding Percentage setting that appears alongside any active textures:

Color Percentage

Building the Datasmith Scene Hierarchy

Datasmith builds its scene hierarchy from your Rhino model as follows:

  • For each layer in your Rhino scene, Datasmith creates an Actor in Unreal to act as the parent for all objects on that layer.
    Note that unlike the layers that are created in the Layers panel of the Unreal Editor, this hierarchy of Actors is not flattened. The Actors are nested exactly like the layers in your Rhino scene.

  • Under the Actor that represents each layer, every instanced block on the corresponding layer is represented by another Actor.

    Warning: Pivot points on Rhino blocks are currently imported at the wrong position in world space.

  • Finally, the Actor that represents each layer and each block contains Static Mesh Actors that represent the actual geometry objects that make up that layer or block.

  • Groups in Rhino do not affect the Unreal scene hierarchy, as they are considered selection helpers rather than important elements in the scene hierarchy.

For example, in the image below, you can see that every layer in the Rhino hierarchy has a counterpart Actor in Unreal. Layers like lights > turn signals, which contain only geometry objects in Rhino, contain only the corresponding Static Mesh Actors in Unreal. The lights layer in Rhino also contains two block instances, named left_headlight and right_headlight. Each of these is represented by a nested Actor in Unreal, which in turn contains the geometry objects that make up those blocks.

Credit: The model used on this page is courtesy of Turbosquid user tomashorin.design.

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