Terrain: DEM & geoid¶
Terrain support for conversion: auto-fetch the covering
Copernicus GLO-30 DEM tiles and the EGM geoid grid, so umbra convert --dem
auto --geoid auto needs no hand-found elevation data.
DEM¶
fetch_dem_for_bbox(bbox, dest_dir=None, *, base=COPERNICUS_DEM_30M_BASE, download=download_url, session=None)
Fetch the Copernicus GLO-30 DEM covering bbox and return a local raster path.
bbox is (west, south, east, north) in EPSG:4326 degrees. Every 1°×1°
tile covering it is downloaded to dest_dir (default
:func:default_dem_cache_dir) via the resume-safe download callable;
tiles Copernicus omits because they are all-ocean (a 404) are skipped. The
return is a single rasterio-openable DEM: the one tile as-is when the bbox
falls in a single cell, or a merged mosaic (dem_mosaic_*.tif in
dest_dir) when it spans several.
Raises :class:DemUnavailableError when no covering tile exists (e.g. a
scene entirely over open water — pass an explicit --dem PATH there).
download is injectable so the whole path is offline-testable without the
bucket; only the multi-tile mosaic step imports rasterio.
Copernicus GLO-30 tile id for the 1°×1° cell whose SW corner is (lat, lon).
Copernicus tiles are named by their south-west integer-degree corner, so
the cell containing a point is found by flooring its coordinates. lat_deg
/ lon_deg are those floored degrees (lat_deg in [-90, 89]).
copernicus_tile_id(45, 6) 'Copernicus_DSM_COG_10_N45_00_E006_00_DEM' copernicus_tile_id(-1, -1) 'Copernicus_DSM_COG_10_S01_00_W001_00_DEM'
Tile ids of every Copernicus DEM cell covering the bbox.
See :func:tiles_covering_bbox for the coverage rule.
Where auto-fetched DEM tiles are cached.
$UMBRA_DEM_DIR overrides everything; otherwise tiles sit beside the
catalog index under the XDG cache dir ($XDG_CACHE_HOME or ~/.cache)
at umbra-py/dem.
Geoid¶
fetch_geoid_grid(dest_dir=None, *, name=DEFAULT_GEOID_GRID, base=PROJ_CDN_BASE, download=download_url, session=None)
Fetch a global geoid-undulation grid and return its local path.
The grid name (default :data:DEFAULT_GEOID_GRID, the EGM96 15′ model) is
downloaded once to dest_dir (default :func:default_geoid_cache_dir) via
the resume-safe download callable and cached there, so a repeat call
re-downloads nothing. The return is a single rasterio-openable raster whose
band 1 is the geoid undulation N in metres — exactly what
:func:umbra_py.convert._geoid_corrected_sampler adds to each sampled DEM
height, so it feeds straight into the --geoid PATH path.
Unlike a DEM there is nothing to tile: the EGM grid is global, so one file
covers every scene and no footprint bbox is needed. download is injectable
so the whole path is offline-testable without the CDN.
Public HTTPS URL of the geoid grid name on the PROJ CDN.
Where the auto-fetched geoid grid is cached.
$UMBRA_GEOID_DIR overrides everything; otherwise the grid sits beside the
catalog index and DEM tiles under the XDG cache dir ($XDG_CACHE_HOME or
~/.cache) at umbra-py/geoid.