Anisotropy is when spatial correlation is directionally dependent. In
`sdmTMB()`

, the default spatial correlation is isotropic, but anisotropy can
be enabled with `anisotropy = TRUE`

. These plotting functions help visualize
that estimated anisotropy.

## Arguments

- object
An object from

`sdmTMB()`

.- return_data
Logical. Return a data frame?

`plot_anisotropy()`

only.- model
Which model if a delta model (only for

`plot_anisotropy2()`

;`plot_anisotropy()`

always plots both).

## Value

`plot_anisotropy()`

: One or more ellipses illustrating the estimated
anisotropy. The ellipses are centered at coordinates of zero in the space of
the X-Y coordinates being modeled. The ellipses show the spatial and/or
spatiotemporal range (distance at which correlation is effectively
independent) in any direction from zero. Uses ggplot2. If anisotropy
was turned off when fitting the model, `NULL`

is returned instead of a
ggplot2 object.

`plot_anisotropy2()`

: A plot of eigenvectors illustrating the estimated
anisotropy. A list of the plotted data is invisibly returned. Uses base
graphics. If anisotropy was turned off when fitting the model, `NULL`

is
returned instead of a plot object.