Datasmith Reimport Guide: Unreal Engine Scenes

This guide is based on the Datasmith reimport and scene transfer workflows described in Epic Games’ Unreal Engine documentation. When a source model changes, you can bring updates into Unreal Engine as a complete scene or as selected assets. However, because reimporting can overwrite some edits made in the Unreal Editor, choose a method based on the scope of the changes. The documentation does not specify a particular Unreal Engine version for these workflows.

1. Full scene or individual assets?

1. If the source file contains new objects or materials, or if objects have moved or their parent relationships have changed, consider a full-scene reimport. This updates the Datasmith Scene asset to reflect the latest state of the source scene.

2. Choose a single-asset reimport if changes are limited to a small number of Static Meshes, materials, or textures and you don’t want to bring in changes to the rest of the scene.

3. A full-scene reimport may be more suitable when the source has many changes or you don’t know which assets have changed. Use the individual-asset method when you need to apply different import settings to specific assets.

A full-scene reimport updates the Datasmith assets in the Content Browser to match the source scene. However, an instance of a Datasmith Scene placed in a Level may not immediately reflect the new hierarchy. The Datasmith Scene Actor in the Level needs to be synchronized with the updated asset. You can automatically update instances in the open Level during import. If the same scene is instanced in different Levels, synchronize each relevant instance separately as needed.

An individual-asset reimport recreates the selected item, even if that item has not changed in the source scene. For example, the geometry of a reimported Static Mesh is rebuilt from scratch, and edits made to the mesh geometry in the Unreal Editor may be lost. Because this method does not update the Datasmith Scene asset, it also does not change the scene hierarchy in the Level.

2. Manage the risk of overwriting Unreal Editor changes

Overrides tracked by Datasmith may be preserved during synchronization, but Unreal Editor changes to imported data that aren’t tracked as overrides may be lost during reimport. Pay particular attention to edits that are part of the source data, such as a Parent Material graph or Static Mesh geometry.

1. Before reimporting, identify which assets have been modified in Unreal Engine. If you need to preserve any edits, plan to back them up or work on a copy before proceeding.

2. If you don’t want to update a type of asset across the board, clear the corresponding Process checkbox in the reimport options. For example, you can disable Materials & Textures to prevent edits to a material graph from being overwritten. Keep in mind that this also excludes other assets of the same type that you may want to update.

3. If you need to keep Unreal Engine-specific changes to an asset, duplicate the original imported asset into another folder and edit the copy. Redirect references to use the copy as well. Recreating the source asset may affect the original, but the separate copy won’t be affected by that operation.

During a full-scene reimport, Static Mesh, Texture, and Material Instance assets are recreated if they have changed in the source file since the last import. Parent Material assets are recreated regardless of whether they have changed in the source. Assets for objects deleted from the source scene are not automatically removed from the Content Browser; they may remain in the project as independent assets. Whether instances in the Level are deleted or updated depends on synchronization and their override state.

3. Check the hierarchy and deleted objects

When the Datasmith Scene Actor in a Level is synchronized, new source objects are added to the Level, while counterparts of objects deleted from the source are generally removed. An Actor corresponding to a deleted object may not be removed automatically if it contains overrides. An Actor previously deleted in Unreal Engine is not restored to the Level by default, even if it still exists in the source; you can change this behavior during synchronization.

Parent-child relationships are also updated to match the hierarchy in the source scene. As a result, reimporting just one mesh won’t bring group or parent changes made in the source file into the Level. If objects have been added, deleted, regrouped, or repositioned, keep the full-scene workflow separate from asset updates.

4. Check scale, surface orientation, and CAD geometry

Datasmith automatically converts the units used in the source application to Unreal Engine’s centimeter-based scale. An object defined as 10 units long in inches in the source becomes 25.4 units long in Unreal Engine. So there’s no need to rescale the source model just because the units differ. The result may vary when non-uniform parent scales are combined with custom pivot transforms; simplifying the transform hierarchy in the source scene may help in that case.

For performance, Unreal Engine generally does not render triangles facing away from the camera. If the source application uses single-sided geometry or inward-facing normals, a surface may appear to disappear from certain angles. Where possible, model pieces that need to be visible from both sides with thickness and outward-facing normals. For a surface that only needs to be visible from one direction, flipping its normal in the source application is another option. You can change Static Mesh surface orientation in the Unreal Editor, but that edit may be lost when the source geometry is reimported.

The Two Sided property for a Material Instance is under General › Material Property Overrides › Two Sided in the Material Editor’s Details panel. Shadow Two Sided is in the Static Mesh Actor’s Details › Lighting section. Don’t use a two-sided material as a blanket fix for every surface: with static or stationary lighting, both sides of a surface may share the same lightmap area, causing visual artifacts.

5. Lightmaps and level of detail for CAD models

For static lighting, Datasmith automatically generates UVs for imported Static Meshes and adds two UV sets. The process aims to arrange mesh surfaces in the lightmap without overlap. If triangles share the same lightmap area, lighting and shadow information may not be separated correctly, causing lighting errors. If you have preconfigured lightmap UV channels in 3ds Max, refer to the relevant guidance in Datasmith’s 3ds Max documentation.

In CAD scenes, reimporting selected Static Meshes with different tessellation settings can help you manage triangle counts on a per-part basis. For example, you can import most of the model at a lower resolution while processing a few important meshes at a higher resolution. Retessellation lets you change the triangle mesh without reimporting the existing geometry from the source CAD file; it generates a new mesh from the most recently imported geometry.

Common mistakes

• Trying to transfer a hierarchy change by reimporting an individual asset: this method does not update the Datasmith Scene asset.

• Assuming all Unreal Editor changes will be preserved: edits to untracked assets may be overwritten.

• Expecting an asset for an object deleted from the source to also be deleted from the Content Browser: the asset may remain in the project.

• Assuming an invisible surface must have failed to import: check the normals and whether the geometry is single-sided.

• Enabling a two-sided material in every case: it may cause artifacts with static or stationary lighting.

Impact on architectural visualization workflows

In architectural projects where the source model is updated frequently, a full-scene reimport lets you bring in new objects and hierarchy changes together. By contrast, individual reimport may be a more controlled choice when you need to change the level of detail of a few CAD parts or update only selected assets. For scenes used in multiple Levels, include synchronization of instances in your update plan.

Identifying modified meshes and materials before importing helps reduce the risk of unexpected overwrites. If the problem is with the geometry or normal orientation, fixing it in the source model can help ensure consistent results in later imports. The documentation does not provide information about hardware, licensing costs, or a specific software version, so teams should evaluate their choices based on their project structure and the edits they need to preserve.