Geometry Streaming

Overview

The External Scene extension streams in geometry from external USD files using an assigned probe. It does this by intersecting the probe with an assigned bounding box to the geometry.

Getting Started

To start using the extension, make sure the External Scene extension is enabled in the extensions manager, located at Windows -> Extension.

Using Geometry Streaming

In this section, we’ll be discussing options for geometry streaming from the External Scene Extension

Prep your geometry

You’ll need to create sets of geometry you want to stream separated into different USD files. For example: city blocks, or sections of a large scene.

Divide up your scene into ways that would visually stream in and out without visual popping.

After separating the different source files, create a new scene and import your files to stream into it.

Add External Scene

Create a transform for your geometry and right click select -> +Add -> External Scene.

or

With the transform selected click the +Add button in the property window and select External Scene.

The External Scene properties have been added to your transform.

Add External Geometry

With your transform selected go to Property -> External Scene and click on the +Add External Scene button.

A Select External Scene window will appear

Navigate to your external scene, select it and click the Select button.

The geometry will be viewable in the Viewport by default and the Asset Path will be added in the window

Note

You can add multiple geometry paths to a single transform.

The file button allows you to select a new path

The delete button will remove the asset from the External Geometry properties.

External Scene Parameters

External Scene Parameters	Description
Add External Scene	This button allows you to add an external scene to your existing geometry
Load	Toggle: if true, the scene will be loaded when the scene is loaded
Auto Load	Toggle: If true, the scene will be loaded when a probe is within the bounding box
Use External Scene bounds	This button will adjust the bound based on the imported geometry
Bound Box Min	Vector 3 is a minimum bounds of an AABB used to auto load the scenes
Bound Box Max	Vector 3 is a maximum bounds of an AABB used to auto load the scenes
Remove External Scene from Prim	This will remove the External Scene from the primitive

Note

Load and Auto Load are mutually exclusive, if one is true the other must be false.

Probes

External Scenes can be loaded and unloaded interactively.

We’ve included a simple probe component to demonstrate that

The extension identifies them by an attribute that is added to the prim.

When a probe intersects a bound, it streams in your geometry. Using this technique the state of an External Scene can be influenced by overlapping the Zform Prm with the External Scene’s world bounding box.

A probe can be any prim. We’ve provided a convenient API that will allow users to design their own control mechanisms. For example: unloading External scenes when outside the camera frustum.

To make a prim into a probe, right click your prim and select +Add -> External Scene probe

Filters and Options

You can create a column for your External Scenes in the Stage window.

go to the Stage window and click on the Options button. Go to Columns -> External Scene

Your column is created in the Stage window.