Covariates the pipeline computes rather than downloads: spatial and temporal gradients, distances to fronts and contours, lags, integrals, and flow diagnostics. The computation is derivoce throughout, which owns the definitions so every consumer computes them identically; this package supplies the config block naming which ones a run wants and threads the results through the rest of the pipeline.
Value
a named list, one entry per supported step type, each with label,
units, description, inputs, neighbourhood, required (extra fields
with no default), and outputs (a function giving the column names a step of
that type produces)
Details
Every entry describes one derivoce function that a covariates.derivoce step
can name. inputs gives the step fields that name covariate columns, with
their defaults: "" marks a field the config must supply, NA an optional one
with no default. neighbourhood marks the steps that read a point's
surroundings rather than only its own value, which is what makes upsampling
matter (see add_derivoce_covariates()).
References
Each step implements a published method, and the citation belongs to that method rather than to this package. derivoce's own help pages carry the reference for each function, and its README collects them; the ones behind the steps here that are not simply arithmetic on the grid:
Belkin IM, O'Reilly JE (2009). An algorithm for oceanic front detection in
chlorophyll and SST satellite imagery. Journal of Marine Systems 78(3),
319-326. doi:10.1016/j.jmarsys.2008.11.018
— distance_to_front
Haller G (2015). Lagrangian coherent structures. Annual Review of Fluid
Mechanics 47, 137-162. doi:10.1146/annurev-fluid-010313-141322
—
ftle, fsle
d'Ovidio F, Fernández V, Hernández-García E, López C (2004). Mixing
structures in the Mediterranean Sea from finite-size Lyapunov exponents.
Geophysical Research Letters 31(17). doi:10.1029/2004GL020328
—
fsle
distance_to_shore measures against Natural Earth coastlines
(https://www.naturalearthdata.com/, public domain), via rnaturalearth.
See also
add_derivoce_covariates(), which runs the configured steps
Examples
names(derivoce_covariates())
#> [1] "horizontal_gradient" "vertical_gradient" "temporal_gradient"
#> [4] "lag_covariate" "integrate_covariate" "current_speed"
#> [7] "eke" "ftle" "fsle"
#> [10] "distance_to_front" "distance_to_contour" "distance_to_isobath"
#> [13] "distance_to_shore"
derivoce_covariates()$horizontal_gradient$units
#> [1] "source units per km"
# The column names a step will produce, before running it.
derivoce_covariates()$lag_covariate$outputs(list(vars = "CHL", n = 2))
#> [1] "CHL_lag2"