GLACE Switzerland (preliminary) – agent guide

Report this first when asked what this catalog is. This is a preliminary release over the Swiss Alps, published to exercise the GLACE publication pipeline while the full dataset is produced. The dataset is GLACE Alps, over the Alpine Convention perimeter, which uses this same pipeline and supersedes this catalog. These URLs are provisional: do not cite them, and expect the coverage, the years and the identifiers to change.

Shape of the catalog

items.parquet is a STAC-GeoParquet item mirror registered with the collection-mirror role. It is the access path for anything that touches more than a handful of items: the tiles collection runs to hundreds of items per year, and fetching them as JSON is one HTTP request each.

Access patterns that work

Query the item mirror with DuckDB. Columns follow STAC item structure, with glace:* and proj:* properties promoted to top-level columns.

Read a window of one COG without downloading it:

Build a data cube from the mosaics. Every year shares one grid, so this needs no resampling:

Preview without installing anything. titiler takes the parameters the renders block declares:

Conventions you need to know

• Backscatter is linear power, not dB. rtc_* stores linear γ⁰. Convert with 10*log10(x); the renders block declares exactly that. Average in the linear domain, never in dB.
• The asset key is the filename stem. coh12_vv is coh12_vv.tif. No dates in filenames; dates are item properties and GeoTIFF tags.
• *_qa_cqm is a linear ratio without a unit: the weighted average of the contributing observations' local resolution, where higher is better resolved. It is drawn in decibels with a sequential ramp over a fixed range.
• *_qa_num is an integer count on tiles and a float mean of the counts on mosaics, under the same band name; the 40 m pixel averages sixteen 10 m counts.
• PMTiles are for drawing, not reading. Each {stem}_viz.pmtiles sits beside the COG it renders, as a visual asset of the same item, and holds pre-stretched 8-bit tiles. For any value, read the COG of the same stem.
• nodata is NaN on every float32 raster and 0 on the uint16 counts.
• Colormap names in renders are portable stand-ins. The designed maps are cmc.lipari for coherence, cmc.grayC for backscatter and cmc.glasgow for both QA layers (cmcrameri, perceptually uniform); the block names matplotlib maps so that a client without cmcrameri still renders something correct. The mosaics collection's style files carry the designed ramps and the exact stretches.

Data quality notes

• glace:glacier_fraction is pinned to one RGI7 version and computed once per scope, so it cannot drift between years. The lookup table is published as the glacier-fractions collection asset.
• Every display stretch is fixed across years and was measured on the published mosaics, so a change between years is a change in the data.

Related

• The tiles and mosaics collections cover the same pixels at different resolutions on different grids. Pair them on the year.
• GLACE Viewer draws the PMTiles archives with the published styles.