CREST

Copernicus Raster Elevation Simulation Toolkit

Browser-based DSM viewer and hydrological flow simulator.
No server. No build step. No framework. Two HTML files.

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What it does

map.html — worldwide satellite map cataloguing your local Copernicus DSM tiles.
Click a green square to open it in the viewer.

dsm.html — full DSM viewer with hydrological flow simulation.
Right-click anywhere on terrain to pour water. Watch it find its own path.

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Features

Feature	Detail
DSM rendering	GeoTIFF COG Float32, native DEFLATE decompression
Colour palette	Hypsometric LUT, histogram equalisation (10 000 bins)
Contour lines	4-neighbour detection, auto interval, major/minor
Flow simulation	Local flood-fill, downhill priority, canyon infiltration
Water overlay	Right-click = source, Space = reset, level rises +1m when blocked
Mouse overlay	Lon/lat DMS WGS84 + elevation or water depth
Altitude legend	Live colour bar, water level indicator
Road overlay	Leaflet + Carto labels (optional, on/off)
Recording	WebM 5 fps via MediaRecorder, auto-download
Tile catalogue	Scans ~/Downloads/copernicus/ — zero upload, filenames only
Communication	BroadcastChannel between tabs, works on file://

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Dependencies

Library	Used in	Why
Leaflet 1.9.4	both files	Satellite basemap + optional road overlay

Everything else is vanilla JavaScript — TIFF parsing, DEFLATE decompression (DecompressionStream), Float32 decoding, histogram equalisation, contour detection, flood simulation, WebM recording — all native browser APIs.

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Data source

Tiles come from the Copernicus DEM GLO-30 (30 m resolution), freely available from AWS:

https://copernicus-dem-30m.s3.amazonaws.com/
Copernicus_DSM_COG_10_{NS}{LAT}_00_{EW}{LON}_00_DEM/
Copernicus_DSM_COG_10_{NS}{LAT}_00_{EW}{LON}_00_DEM.tif

Expected local structure:

~/Downloads/copernicus/
  Copernicus_DSM_COG_10_N04_00_W053_00_DEM/
    Copernicus_DSM_COG_10_N04_00_W053_00_DEM.tif
  Copernicus_DSM_COG_10_S20_00_E169_00_DEM/
    Copernicus_DSM_COG_10_S20_00_E169_00_DEM.tif
  ...

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Usage

# 1. Clone
git clone https://github.com/yourname/crest.git
cd crest

# 2. Open map.html in Chrome or Firefox — no server needed
# 3. Click "Ouvrir copernicus/" and point to ~/Downloads/copernicus/
# 4. Green squares appear for every tile found locally
# 5. Click a green square — dsm.html opens and loads the tile

Popup note — Chrome may block the dsm.html popup on first use.
Allow popups for file:// and click again.

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Controls

map.html

Action	Result
Click green square	Open tile in dsm.html

dsm.html

Action	Result
Scroll wheel	Zoom (cursor-centred)
Drag	Pan
Right-click	Place water source
Space	Reset simulation
⇄ button	Toggle hypsometry / contour lines
🗺 button	Toggle road & label overlay
⏺ REC button	Start/stop WebM recording

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Flow simulation

Water follows local terrain at each step:

1. Downhill flow — spreads to the lowest accessible border pixel each tick
2. Flat terrain — spreads to all pixels at equal minimum elevation
3. Basin filling — when blocked, water level rises +1 m per tick
4. Canyon infiltration — beyond 10 m of accumulated rise, penetration increases by +2 m/tick to overcome averaging artefacts in 30 m pixels
5. Ocean stop — simulation halts when water reaches sea level

Status bar shows: surface elevation · accumulated rise · pixel count · active front size.

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Architecture

crest/
├── map.html          # Tile catalogue — Leaflet satellite + grid layer
├── dsm.html          # DSM viewer + flow simulator
└── README.md

Inter-tab communication: BroadcastChannel('crest_dsm')
map.html passes the File object directly — no re-upload, no copy.

Decompression pipeline:

.tif → ArrayBuffer → TIFF tags → tile offsets
     → Uint8Array(compressed) → DecompressionStream('deflate-raw')
     → Float32 predictor decode → elevGrid + OffscreenCanvas

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Browser compatibility

Browser	Minimum version
Chrome / Edge	80+
Firefox	113+
Safari	16.4+

Required APIs: DecompressionStream, OffscreenCanvas, BroadcastChannel, MediaRecorder.

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Changelog

Version	Change
2.0	Replaced pako with native DecompressionStream — sharper output, zero dependency
1.9	Reverted to local flood-fill (Manning removed), RAF full speed
1.8	Altitude legend panel, RAF loop
1.7	WebM 5 fps recording (MediaRecorder)
1.6	Canyon infiltration (+2 m/tick beyond 10 m rise)
1.5	Local flood-fill — water flows from adjacent wet pixel, not global level
1.4	Water level rises +1 m when blocked, mouse shows water depth
1.3	Flow simulation — right-click source, Space reset
1.2	Carto overlay on/off (light_only_labels, transparent container)
1.1	BroadcastChannel replacing postMessage (file:// compatibility)
1.0	map.html + dsm.html, tile catalogue, hypsometry, contour lines

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Licence

MIT — see LICENSE.

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Built by eperret with the Help of AI Claude Sonnet 4.6 / Anthropic — May 2026