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_earth_curvature_drop(distance_m, refraction=0.13) (to call the implementation directly, import demops; demops.dem_earth_curvature_drop(distance_m, refraction=0.13); from the registry, opsdem.get("dem_earth_curvature_drop"))
Earth-curvature drop [m] for line-of-sight computations. (1 - k) d^2 / (2 R).
Distant ground appears lowered by the Earth's curvature, and atmospheric refraction partly cancels this. Guide values for the standard atmosphere (k = 0.13):
========== ================ ================
Distance Curvature only With refraction
========== ================ ================
1 km 0.078 m 0.068 m
5 km 1.962 m 1.707 m
10 km 7.848 m 6.828 m
30 km 70.63 m 61.45 m
========== ================ ================
For a line of sight 30 km away the ground drops by more than 60 m, so a viewshed computed as a plane is meaningless at that distance. refraction is a conventional value for the standard atmosphere, not a constant —— in a night-time inversion layer it can be negative or even 0.25.
• dem_terrain_analysis family guide
• 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.
• dem_geodesy_tour — py -3.11 examples/dem_geodesy_tour.py
• poc_geodetic_height_frames — py -3.11 examples/poc_geodetic_height_frames.py
measurement as input)—
geodesy)dem_geodetic_to_ecef · dem_ecef_to_geodetic · dem_geocentric_grid · dem_cell_size_webmercator · 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).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.