GravityModels API

This document describes the API required for a gravity model. The user can add new models by overloading the functions listed here.

Structure

All models require a structure with supertype AbstractGravityModel{T<:Number}, where T is the type of the coefficients in the model.

API Functions

function coefficients(model::AbstractGravityModel{T}, degree::Int, order::Int, time::DataTime) where T<:Number -> T, T

This function must return the coefficients Clm and Slm of the gravity model for the specified degree, order, and time. Hence:

coefficients(model, 10, 8, DateTime("2023-06-19"))

must return a Tuple{T, T} with the Clm and Slm, respectively, for the degree 10, order 8, and computed at day 2023-06-19.

Note If the model has constant coefficients, the function must still accept the positional argument time, but it will be neglected.

function coefficient_norm(model::AbstractGravityModel) where T<:Number -> Symbol

This function must return the normalization we must use in the spherical harmonics when computing the Legendre associated functions. The accepted values are:

• :full: Use full normalization.
• :schmidt: Use Schmidt quasi-normalization.
• :unnormalized: Do not perform normalization.

function gravity_constant(model::AbstractGravityModel{T}) where T<:Number -> T

This function must return the gravity constant [m³ / s²] for the gravity model.

function load(::Type{T}, args...; kwargs...) where T<:AbstractGravityModel -> T

This function must return gravity model structure, which is loaded using the arguments args... and keywords kwargs....

function maximum_degree(model::AbstractGravityModel) -> Int

This function must return the maximum degree of the gravity model.

function radius(model::AbstractGravityModel{T}) where T<:Number -> T

This function must return the radius [m] for the gravity model.