Overview#

omni.usd.schema.geospatial provides USD schema definitions for representing geospatial coordinate systems and geodetic positions within USD scenes. This extension enables the integration of real-world geographic coordinate systems into USD stages, allowing prims to be positioned using WGS84 geodetic coordinates (latitude, longitude, altitude) that can be transformed to local Cartesian coordinate systems.

Concepts#

Geodetic Coordinate Systems#

The extension implements a coordinate transformation system that converts between geodetic WGS84 coordinates and local Cartesian coordinates. WGS84 positions are represented as (latitude, longitude, altitude) where longitude and latitude are in degrees and altitude is in meters above the surface, regardless of the stage’s metersPerUnit setting.

Reference Frame Hierarchy#

The schema system operates on a hierarchical reference model where local positions are defined relative to reference positions within the prim hierarchy. Each local position must have a corresponding reference position defined by the same prim or a parent prim to establish the coordinate transformation context.

Key Components#

WGS84ReferencePositionAPI #

WGS84ReferencePositionAPI establishes the reference point and coordinate frame parameters for geodetic coordinate transformations. This schema defines the target reference point for translating geodetic coordinates to Cartesian coordinates in a specified tangent plane coordinate system.

The schema supports transformation through the Earth Centered Earth Fixed (ECEF) coordinate system to either East-North-Up (ENU) or North-East-Down (NED) local coordinate systems, with configurable orientation parameters for Yaw, Pitch, and Roll rotations.

WGS84LocalPositionAPI #

WGS84LocalPositionAPI defines geodetic positions for individual prims relative to a reference position in the prim hierarchy. This schema allows prims to specify their world position using geodetic coordinates while maintaining proper transformation to the local Cartesian coordinate system.

Local positions are always relative to the first reference position found in the parent hierarchy. If no reference position is defined in the hierarchy, the local position schema should be ignored.

Tokens #

The Tokens class provides standardized token definitions for the geospatial schema system, including coordinate frame identifiers (ENU, NED) and schema attribute names used throughout the geospatial coordinate transformation pipeline.

Limitations#

The schemas enforce that WGS84ReferencePositionAPI and WGS84LocalPositionAPI cannot be applied to the same prim simultaneously, as this would create an undefined coordinate transformation state. Additionally, both schemas can only be applied to Xformable prims, ensuring proper integration with USD’s transformation system.