> ## Documentation Index
> Fetch the complete documentation index at: https://www.agentworldprotocol.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Grounding

> Shared conventions — units, frames, clocks, encodings — so payloads mean the same thing in every world.

Interoperability dies in the details, so Layer 3 pins them down:

* **Units** — SI everywhere, encoded in field names (`_m`, `_rad`, `_mps`, `_n`). No implicit unit negotiation. See [units and frames](/spec/semantics/units-and-frames).
* **Coordinate frames** — right-handed, with an explicit **frame tree** (named frames and parent transforms) published at `session.ready`, borrowed conceptually from ROS tf. Every pose names its frame.
* **Time** — monotonic nanosecond timestamps against a session clock, anchored to wall-clock and (in sims) to sim-time. See [timestamps and clocks](/spec/semantics/timestamps-and-clocks).
* **Modalities** — a registry of standard encodings (`image/jpeg`, `audio/pcm`, `proprio/json`, `text/event+json`, …) with `x-vendor.*` extension naming. See [modalities](/spec/semantics/modalities).
* **Scene graphs** — an optional semantic channel exposing entities, affordances, and relations as structured JSON. Enormously valuable for LLM agents that reason in symbols rather than pixels. See [scene graphs](/spec/semantics/scene-graphs).