louis-e/arnis · error · Error

No preview data available

Error message

No preview data available

What it means

ensureProtocol registers a custom maplibregl protocol handler for arnisdem:// URLs; when maplibre requests a tile, the handler parses the dataset id from the URL and looks it up in the module-local datasets Map. If no dataset with that id is registered (or the regex doesn't match), the handler rejects with this Error, surfacing as a failed tile request in the map.

Source

Thrown at src/gui/js/preview3d.js:199

        px[i++] = whole % 256;
        px[i++] = Math.floor((e - whole) * 256);
        px[i++] = 255;
      }
    }
    return img;
  }

  // The terrain and hillshade sources request every tile with the same URL;
  // caching the synthesized ImageData halves the per-tile sampling work.
  const tileCache = new Map();
  const TILE_CACHE_MAX = 48;

  function ensureProtocol() {
    if (protocolRegistered) return;
    maplibregl.addProtocol(PROTOCOL, async (params) => {
      const m = params.url.match(/^arnisdem:\/\/(\d+)\/(\d+)\/(\d+)\/(\d+)/);
      const d = m && datasets.get(+m[1]);
      if (!d) throw new Error("No preview data available");
      let img = tileCache.get(params.url);
      if (!img) {
        img = renderDemTile(d, +m[2], +m[3], +m[4]);
        tileCache.set(params.url, img);
        if (tileCache.size > TILE_CACHE_MAX) {
          tileCache.delete(tileCache.keys().next().value);
        }
      }
      return { data: await createImageBitmap(img) };
    });
    protocolRegistered = true;
  }

  function landCoverUrl(grid, gw, gh) {
    const canvas = document.createElement("canvas");
    canvas.width = gw;
    canvas.height = gh;
    const ctx = canvas.getContext("2d");

View on GitHub (pinned to 34048924d9)

Solutions

1. Ensure the dataset is registered via datasets.set(id, d) before adding/using any arnisdem:// source, and keep the id consistent with the tile URLs in the source.
2. Remove the map source and detach the map when the dataset is deleted/regenerated instead of leaving stale arnisdem:// URLs live.
3. Catch the rejection in the protocol handler flow (maplibre surfaces it as a source error event); listen to map.on('error') and ignore/suppress errors for known-stale dataset ids.
4. If ids are derived from user input, validate they are numeric before building arnisdem:// URLs.
5. Clear tileCache and rebuild the source with the new dataset id whenever the preview is regenerated.

Example fix

// before
map.setTerrain({ source: "dem", ... }); // dem source still uses old arnisdem://7/... id after regen
// after
map.on("error", (e) => {
  if (String(e.error && e.error.message).includes("No preview data available")) return; // stale tile
  console.error(e);
});
// and on regeneration:
if (map.getSource("dem")) map.removeSource("dem");
addDemSource(map, newDatasetId);

const ds = typeof datasetId === "number" && Number.isInteger(datasetId) ? datasetId : null;
if (ds == null || !datasetRegistryHas(ds)) { skipMapSetup(); return; }

function hasDataset(id) { return Number.isInteger(id) && datasets.has(id); }

map.on("error", (e) => {
  if (e && e.error && e.error.message === "No preview data available") return; // stale tile for old dataset
  console.error("map error:", e);
});

When it happens

Trigger: A maplibre source with tiles under arnisdem://<datasetId>/... is still attached to a live map after the dataset was removed from the datasets Map (e.g. preview regenerated, selection cleared, or module state reset), or the URL does not match the /^arnisdem:\/\/(\d+)\/(\d+)\/(\d+)\/(\d+)/ pattern (e.g. non-numeric id), so `d` is undefined.

Common situations: Stale DEM tile requests from a previous map instance racing with a regenerated preview; a cached map style JSON referencing an old dataset id; calling createTerrainMap before the dataset was added to the registry; hot module reload clearing the module-level Map while the map keeps requesting tiles.

Related errors

• Unexpected preview payload format
• land cover grid mismatch
• Failed to get main window
• Error while starting the application UI (Tauri)

AI-assisted analysis of louis-e/arnis@34048924d9 (2026-09-03). Data as JSON: /api/errors/55096fc25cfbe1c2. Report an issue: GitHub.