Memento experiment

Memento is a built-in Experiment mode in spARcl, created for our ISMAR2026 tutorial. In AR, after localization, you pick a 3D model, preview it on a hit-test reticle, and place it at your feet. The client writes two Spatial Content Records (SCRs) to a Spatial Content Discovery (SCD) service so you and others can see the same mementos when querying the same map cell and topic again.

Implementation lives under src/experiments/oarc/memento/.

Models

Models are served from public/media/models/memento/ but note that all users must use the same spARcl deployment to access to models.

In our ISMAR2026 tutorial, we used models from 3d-emoji-assets-generator (CC-BY-4.0), but we do not want to add these to git. Specific to these models, the code uses the kMementoModelSizePercent, kMementoTextSizePercent, kMementoModelOriginToBottomModelUnits, kTextHeightOffsetM variables to place these models on the ground. If you use other models, you will need to adjust or remove these numbers.

Serving models from other external URLs requires a little refactoring.

What it does

  1. Localize — Uses the normal spARcl viewer flow (GeoPose / world alignment). Placement is only allowed when alignment is active.
  2. Browse models — Loads catalog.json and shows a list of model labels. The selected model is previewed on the hit-test reticle.
  3. Place here — On confirm, posts to SCD:
    • A MODEL_3D SCR: GLB from the catalog, SPIN_UP animation
    • A TEXT SCR: display name from SCD Auth0 profile in description (and title), floating ~2 m above the model, content.size 20, billboard toward camera.
  4. Discover others’ mementos — Enables periodic H3 content re-query on the configured SCD topic (default history) via the parent Viewer.svelte, same as other OSCP content.

How to run it (developers and testers)

Dashboard

  1. Open the Dashboard (tap the top-right corner of the screen).
  2. Set AR mode to Experiment.
  3. Choose Memento in the experiment selector.
  4. Configure Memento settings (see below).
  5. In Application state, ensure a content service that points at your SCD (or the default demo SCD) is selected, so placed and existing mementos can be retrieved.
  6. Start AR from the main UI.

Rendering engine

Memento preview and placement use GLB loading. Use the Three.js engine (for example ?engine=three in the URL). The OGL engine does not support complex indexed models.

SCD Auth0 (required to place)

Placing a memento calls postContent and needs an access token with create:scrs. This is separate from logging into the spARcl app.

Add to your .env (see also the root README):

VITE_SCD_AUTH_AUTH0_DOMAIN="your-scd-auth0-domain.auth0.com"
VITE_SCD_AUTH_AUTH0_CLIENTID="your-scd-client-id-from-auth0"
VITE_SCD_AUTH_AUTH0_AUDIENCE="https://your-scd.your-domain.com"
VITE_SCD_AUTH_AUTH0_SCOPE="openid profile email create:scrs"
VITE_AUTH_REDIRECT_URI="YOUR_APP_REDIRECTION_URI"

In the dashboard, under Memento settings, use Sign in to SCD. Default SCD URL is https://scd.orbit-lab.org if left empty.

Topic is fixed to history in code (DEFAULT_MEMENTO_TOPIC in Settings.svelte); the topic field in settings is disabled and always normalized to that value when placing or syncing the content query.

Seeing TEXT labels (name tags)

Posted name tags use SCR type TEXT. The main viewer only renders TEXT when Enable OGC PoI contents is checked on the dashboard (debug_enableOGCPoIContents). Turn that on when testing Memento end-to-end, or name labels will not appear even though the MODEL_3D emoji loads.

Device capabilities

The experiment requests WebXR features: dom-overlay, camera-access, hit-test, and local-floor. You need a browser and device that support hit testing for the reticle and preview.

Filling in catalog.json

Location 

public/media/models/memento/catalog.json

At runtime the client fetches:

/media/models/memento/catalog.json

Each catalog file must be a basename of a GLB in the same directory:

public/media/models/memento/<file>

JSON shape

The file must be a JSON array. Each element is an object with two required string fields:

Field Meaning
file GLB filename only (e.g. camera.glb). No path, no URL. Must be non-empty after trim.
label Short text shown in the model picker and stored in the MODEL_3D SCR description / keywords.

Invalid entries (missing file or label, empty file) are dropped. If the array is empty, the file is missing, or HTTP fetch fails, the overlay shows No models are available and placement stays disabled.

Example

After adding GLBs under public/media/models/memento/:

[
  { "file": "camera.glb", "label": "Camera" },
  { "file": "gift.glb", "label": "Gift" },
  { "file": "flamingo.glb", "label": "Flamingo" }
]

The first entry becomes the default selection when the catalog loads.

Developer checklist for new models

  1. Copy or generate binary GLB files into public/media/models/memento/.
  2. Add one { "file", "label" } object per GLB to catalog.json.
  3. Keep file exactly equal to the on-disk name (case-sensitive on Linux servers).
  4. Prefer glTF binary (.glb) with contentType model/gltf-binary as used when posting SCRs (URLs are /media/models/memento/<file>).
  5. Reload the app (or restart dev server) so the static catalog and new GLBs are served.

You do not register models in TypeScript: the catalog is the only picker configuration. Constants such as model scale (kMementoModelSizePercent) and ground offset (kMementoModelOriginToBottomModelUnits) are shared for all emoji-style assets in Viewer.svelte; custom GLB layouts may need code changes if they are not center-origin with a similar bounding box.

In-session UI

After localization, the Memento overlay provides:

  • Relocalize — Same as the main viewer relocalize control.
  • Place here — Enabled when a model is selected, hit-test reticle is active, world alignment exists, and SCD sign-in is ready (when Auth0 is configured).
  • Horizontal model browser driven entirely by catalog.json.

Errors such as missing SCD token or failed postContent are shown above the toolbar.

Piece Path
Experiment viewer src/experiments/oarc/memento/Viewer.svelte
Dashboard settings src/experiments/oarc/memento/Settings.svelte
Session overlay src/experiments/oarc/memento/Overlay.svelte
SCD Auth0 helper src/experiments/oarc/memento/scdAuth0Service.ts
Experiment registration src/experiments/Selector.svelte (memento key)
Parent content query / SCR dispatch src/components/Viewer.svelte

For general experiment wiring, see Creating an experiment and Integrating experiments.

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