dem_cell_size_webmercator — DEM `geodesy` op

• Data kinds: none → measurement (an op determined by its arguments alone — it takes no image or data input)

• Call: import fullseye as fs; fs.ledger.dem_cell_size_webmercator(zoom, lat_deg) (to call the implementation directly, import demops; demops.dem_cell_size_webmercator(zoom, lat_deg); from the registry, opsdem.get("dem_cell_size_webmercator"))

Usage

Ground resolution of a Web Mercator tile [m/px]. It varies with latitude.

156543.03392804097 * cos(lat) / 2^zoom (for 256 px tiles).

Measured guide: Tokyo (35.68 degrees north) at z=15 gives 3.880 m, the equator 4.777 m. Using the equator value as is makes slopes in Tokyo 23 % too small —— this throws no exception and skews every downstream number, making it the most common accident in this family.

Detailed usage guide

• dem_terrain_analysis family guide

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

• The canonical algorithm (author, year) and its uses are named in the family usage guide above.

Runnable examples (verified samples that actually call this op)

• dem_geodesy_tour — py -3.11 examples/dem_geodesy_tour.py

Ops the type connects to (they accept `measurement` as input)

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Same category (`geodesy`)

dem_geodetic_to_ecef · dem_ecef_to_geodetic · dem_geocentric_grid · dem_earth_curvature_drop · dem_geodetic_slope · dem_geoid_height · dem_height_frame_convert · dem_height_frame_residual

*Provenance: demops.py — DEM operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

dem_cell_size_webmercator — DEM geodesy op