Mastering Omniverse for Robotics
================================

NVIDIA Omniverse offers a large suite of tools for 3D content workflows.
There are three main components (relevant to robotics) in Omniverse:

-  **USD Composer**: This is based on a novel file format (Universal Scene
   Description) from the animation (originally Pixar) community that is
   used in Omniverse
-  **PhysX SDK**: This is the main physics engine behind Omniverse that
   leverages GPU-based parallelization for massive scenes
-  **RTX-enabled Renderer**: This uses ray-tracing kernels in NVIDIA RTX
   GPUs for real-time physically-based rendering

Of these, the first two require a deeper understanding to start working
with Omniverse and its constituent applications (Isaac Sim and Isaac Lab).

The main things to learn:

-  How to use the Composer GUI efficiently?
-  What are USD prims and schemas?
-  How do you compose a USD scene?
-  What is the difference between references and payloads in USD?
-  What is meant by scene-graph instancing?
-  How to apply PhysX schemas on prims? What all schemas are possible?
-  How to write basic operations in USD for creating prims and modifying
   their attributes?


Part 1: Using USD Composer
--------------------------

While several `video
tutorials <https://www.youtube.com/@NVIDIA-Studio>`__ and
`documentation <https://docs.omniverse.nvidia.com/>`__ exist
out there on NVIDIA Omniverse, going through all of them would take an
extensive amount of time and effort. Thus, we have curated these
resources to guide you through using Omniverse, specifically for
robotics.

Introduction to Omniverse and USD

-  `What is NVIDIA Omniverse? <https://youtu.be/dvdB-ndYJBM>`__
-  `What is the USD File Type? \| Getting Started in NVIDIA Omniverse <https://youtu.be/GOdyx-oSs2M>`__
-  `What Makes USD Unique in NVIDIA Omniverse <https://youtu.be/o2x-30-PTkw>`__

Using Omniverse USD Composer

-  `Introduction to Omniverse USD Composer <https://youtu.be/_30Pf3nccuE>`__
-  `Navigation Basics in Omniverse USD Composer <https://youtu.be/kb4ZA3TyMak>`__
-  `Lighting Basics in NVIDIA Omniverse USD Composer <https://youtu.be/c7qyI8pZvF4>`__
-  `Rendering Overview in NVIDIA Omniverse USD Composer <https://youtu.be/dCvq2ZyYmu4>`__

Materials and MDL

-  `Five Things to Know About Materials in NVIDIA Omniverse <https://youtu.be/C0HmcQXaENc>`__
-  `How to apply materials? <https://docs.omniverse.nvidia.com/materials-and-rendering/latest/materials.html#applying-materials>`__

Omniverse Physics and PhysX SDK

-  `Basics - Setting Up Physics and Toolbar Overview <https://youtu.be/nsJ0S9MycJI>`__
-  `Basics - Demos Overview <https://youtu.be/-y0-EVTj10s>`__
-  `Rigid Bodies - Mass Editing <https://youtu.be/GHl2RwWeRuM>`__
-  `Materials - Friction Restitution and Defaults <https://youtu.be/oTW81DltNiE>`__
-  `Overview of Simulation Ready Assets Physics in Omniverse <https://youtu.be/lFtEMg86lJc>`__

Importing assets

-  `Omniverse Create - Importing FBX Files \| NVIDIA Omniverse Tutorials <https://youtu.be/dQI0OpzfVHw>`__
-  `Omniverse Asset Importer <https://docs.omniverse.nvidia.com/extensions/latest/ext_asset-importer.html>`__
-  `Isaac Sim URDF impoter <https://docs.isaacsim.omniverse.nvidia.com/latest/robot_setup/ext_isaacsim_asset_importer_urdf.html>`__


Part 2: Scripting in Omniverse
------------------------------

The above links mainly introduced how to use the USD Composer and its
functionalities through UI operations. However, often developers
need to write scripts to perform operations. This is especially true
when you want to automate certain tasks or create custom applications
that use Omniverse as a backend. This section will introduce you to
scripting in Omniverse.

USD is the main file format Omniverse operates with. So naturally, the
APIs (from OpenUSD) for modifying USD are at the core of Omniverse.
Most of the APIs are in C++ and Python bindings are provided for them.
Thus, to script in Omniverse, you need to understand the USD APIs.

.. note::

   While Isaac Sim and Isaac Lab try to "relieve" users from understanding
   the core USD concepts and APIs, understanding these basics still
   help a lot once you start diving inside the codebase and modifying
   it for your own application.

Before diving into USD scripting, it is good to get acquainted with the
terminologies used in USD. We recommend the following `introduction to
USD basics <https://www.sidefx.com/docs/houdini/solaris/usd.html>`__ by
Houdini, which is a 3D animation software.
Make sure to go through the following sections:

-  `Quick example <https://www.sidefx.com/docs/houdini/solaris/usd.html#quick-example>`__
-  `Attributes and primvars <https://www.sidefx.com/docs/houdini/solaris/usd.html#attrs>`__
-  `Composition <https://www.sidefx.com/docs/houdini/solaris/usd.html#compose>`__
-  `Schemas <https://www.sidefx.com/docs/houdini/solaris/usd.html#schemas>`__
-  `Instances <https://www.sidefx.com/docs/houdini/solaris/usd.html#instancing>`__
   and `Scene-graph Instancing <https://openusd.org/dev/api/_usd__page__scenegraph_instancing.html>`__

As a test of understanding, make sure you can answer the following:

-  What are prims? What is meant by a prim path in a stage?
-  How are attributes related to prims?
-  How are schemas related to prims?
-  What is the difference between attributes and schemas?
-  What is asset instancing?

Part 3: More Resources
----------------------

- `Omniverse Glossary of Terms <https://docs.isaacsim.omniverse.nvidia.com/latest/reference_material/reference_glossary.html>`__
- `Omniverse Code Samples <https://docs.omniverse.nvidia.com/dev-guide/latest/programmer_ref.html>`__
- `PhysX Limitations <https://docs.isaacsim.omniverse.nvidia.com/latest/physics/physics_resources.html>`__
- `PhysX Documentation <https://nvidia-omniverse.github.io/PhysX/physx/>`__.
