Support some physical geodesy and generic geophysical operations

[busstoptaktik]

Explore some roads toward a more smooth handling of parametric and gravity related height systems in ISO 19111/OGC Topic 2, by providing access to some geophysical context.

As a start:

• [x] Normal gravity models, for conversion between gravity and gravity anomalies
  • https://encyclopedia.pub/entry/33797
• [ ] Conversion between the "tide free", "mean tide", and "zero tide" systems
  • ICEsat geodesy guide
• [ ] Normal atmosphere and ocean models for approximate parametric/metric conversions
  • https://en.wikipedia.org/wiki/Atmospheric_pressure
• [x] Deflections of the vertical (ξ, η) from the astronomical (Φ, Λ) and geodetic (φ, λ) latitude and longitude https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017334/ the local gradient of a geoid model