Scripting OpenUSD data interchange: Worked Example — Data Exchange (NVIDIA-Certified Professional: OpenUSD Development)

Scripting OpenUSD Data Interchange: A Worked Example

In the context of the NVIDIA-Certified Professional: OpenUSD Development certification, scripting OpenUSD data interchange is a critical skill. This involves automating the import and export of USD (Universal Scene Description) data to enable seamless data exchange between 3D content creation tools and pipelines.

Below is a detailed, step-by-step worked example demonstrating how to script a simple OpenUSD data interchange task using Python and the USD Python API. The scenario involves exporting a custom 3D scene with basic geometry and then importing it back to verify the data integrity.

Scenario

You are tasked with creating a script that:

• Creates a USD stage with a simple geometric primitive (a cube).
• Sets some custom attributes on the cube.
• Exports the stage to a USD file.
• Imports the USD file back and reads the attributes to verify the data.

Step 1: Setting Up the Environment

Ensure you have the USD Python bindings installed and accessible in your environment. Import the necessary modules:

from pxr import Usd, UsdGeom, Sdf

Step 2: Creating a USD Stage and Adding Geometry

Create a new USD stage in memory and define a cube primitive:

stage = Usd.Stage.CreateNew("example_scene.usda") cube = UsdGeom.Cube.Define(stage, "/World/Cube")

Set the size of the cube:

cube.CreateSizeAttr(2.0)

Step 3: Adding Custom Attributes

Add a custom string attribute to the cube to store metadata, for example, the material name:

cube.CreateCustomDataAttr().Set({"material": "plastic_blue"})

Alternatively, you can use the CreateAttribute method:

cube.CreateAttribute("custom:material", Sdf.ValueTypeNames.String).Set("plastic_blue")

Step 4: Saving the USD Stage

Save the stage to disk:

stage.GetRootLayer().Save()

Step 5: Importing the USD File and Reading Data

Open the saved USD file and access the cube primitive:

imported_stage = Usd.Stage.Open("example_scene.usda") imported_cube = UsdGeom.Cube(imported_stage.GetPrimAtPath("/World/Cube"))

Read the size attribute:

size = imported_cube.GetSizeAttr().Get()

Read the custom material attribute:

material = imported_cube.GetPrim().GetAttribute("custom:material").Get()

Step 6: Verification and Output

Print the values to verify correct data interchange:

print(f"Cube size: {size}") print(f"Cube material: {material}")

Worked Example Summary

Problem: Automate the creation, export, and import of a USD scene containing a cube with custom attributes.

Solution Steps:

1. Import USD Python API modules.
2. Create a new USD stage and define a cube primitive.
3. Set the cube size and add a custom attribute for material.
4. Save the USD stage to a file.
5. Open the USD file and retrieve the cube primitive.
6. Read and print the cube's size and custom material attribute to verify.

This scripting approach enables developers to build custom importers/exporters and automate data exchange workflows efficiently, a key competency for the NVIDIA-Certified Professional: OpenUSD Development exam.

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