Creating data mapping documents: Worked Example — Data Exchange (NVIDIA-Certified Professional: OpenUSD Development)

Creating Data Mapping Documents: A Worked Example for OpenUSD Development

In the NVIDIA-Certified Professional: OpenUSD Development certification, data exchange is a critical topic, especially the creation of data mapping documents. These documents serve as blueprints that define how data from one format or pipeline maps to USD schemas and structures, enabling seamless interoperability in 3D content creation pipelines.

Scenario Overview

Imagine you are tasked with integrating a proprietary 3D asset format, Proprietary3D, into an OpenUSD-based pipeline. Your goal is to create a data mapping document that clearly defines how Proprietary3D attributes correspond to USD attributes, facilitating the development of custom importers and exporters.

Step 1: Analyze Source and Target Data Structures

Begin by thoroughly understanding the Proprietary3D format:

• List all relevant attributes (e.g., geometry, materials, transforms).
• Note data types and hierarchies.

Next, review the USD schemas that will represent these attributes, such as UsdGeomMesh for geometry and UsdShadeMaterial for materials.

Step 2: Define Mapping Objectives

Clarify what data must be preserved during import/export:

• Vertex positions → points attribute in UsdGeomMesh
• Normals → normals attribute
• Material assignments → UsdShadeMaterial bindings
• Transformations → xformOp:transform

Step 3: Create the Data Mapping Document Structure

Organize the document into sections:

1. Source Attribute: Name and type in Proprietary3D
2. Target USD Attribute: Corresponding USD schema and attribute
3. Data Type Conversion: Any required conversions (e.g., float array to VtArray)
4. Notes: Special handling or constraints

Step 4: Populate the Document with Mappings

Example entries:

Source Attribute	Target USD Attribute	Data Type Conversion	Notes
vertex_positions (float3 array)	UsdGeomMesh.points	Direct mapping to VtVec3fArray	Ensure coordinate system alignment
vertex_normals (float3 array)	UsdGeomMesh.normals	Direct mapping	Normalize vectors if necessary
material_id (integer)	UsdShadeMaterial binding	Map ID to material path	Requires material lookup table
transform_matrix (4x4 float)	UsdGeomXformOp.transform	Convert to GfMatrix4d	Apply coordinate system transform

Step 5: Review and Validate the Document

Check for completeness and clarity. Confirm that all source attributes have a corresponding USD target and that data type conversions are feasible within the USD API.

Step 6: Use the Document to Guide Scripting

This mapping document will guide the development of custom importers/exporters. For example, when scripting the importer, you will:

• Read Proprietary3D vertex positions and convert them to VtVec3fArray.
• Assign these to UsdGeomMesh.points.
• Bind materials using the mapped material paths.

Summary

Creating a data mapping document is a foundational step in OpenUSD data exchange workflows. This worked example demonstrates a structured approach to mapping proprietary format attributes to USD schemas, ensuring accurate and efficient data interchange.

For more detailed guidance on OpenUSD development and data exchange, refer to the official NVIDIA resources and documentation.

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