Map covariates on an unstructured mesh, or anywhere else

plot_env() rasterises, which is right for a regular grid and wrong for an FVCOM mesh: a triangulation has no rows and columns to rasterise onto, so the result is either blocky or interpolated over cells the model does not have. This draws the geometry it is given.

Usage

plot_mesh(
  x,
  var = NULL,
  values = NULL,
  time = 1,
  palette = "viridis",
  border = NA,
  main = NULL,
  ...
)

Arguments

x: an sf object with polygon or point geometry — typically from fvcom_mesh(), but any sf object works
var: which column to shade by; NULL draws the bare geometry
values: optional sf object holding the values, from accessFVCOM() or any access function. Joined to x spatially.
time: which time step of values to use, as an index or a named vector of YEAR/MONTH/DAY. Only needed when values carries more than one.
palette: a grDevices::hcl.colors() palette name
border: colour for cell edges. NA hides them, which is what you want on a fine mesh where the edges would otherwise be all you see.
main: plot title
...: passed to plot()

Value

the sf object that was drawn, invisibly, with the joined column if values was given

What it is for

Two jobs. With a mesh from fvcom_mesh() and nothing else, it draws the grid itself — which is how you see where a model resolves a shelf finely and where it does not. With var naming a column, it shades each cell by that value.

Shading a mesh with fetched values

accessFVCOM() returns points and fvcom_mesh() returns triangles, so the two are joined spatially rather than by position — a fetch is subset to the bounding box, so its row order says nothing about the mesh's own numbering. Pass values and that join is done for you:

mesh <- fvcom_mesh(bounding_box = bb)
sst  <- accessFVCOM(vars = "SST", years = 2010, months = 6, bounding_box = bb)
plot_mesh(mesh, "SST", values = sst)

Element-centred values (UO, UBAR, TAUX) sit at the centroid, one per triangle. Node-centred ones (SST, BOTS) sit at the corners, shared between the triangles meeting there, so each triangle takes the mean of its three — which is why the join tests intersection rather than containment: a corner is on the boundary, and nothing contains it.

Examples

if (FALSE) { # \dontrun{
bb <- list(xmin = -70, xmax = -66, ymin = 41, ymax = 44)
mesh <- fvcom_mesh(bounding_box = bb)

plot_mesh(mesh)                      # the grid itself
plot_mesh(mesh, "DEPTH")             # shaded by bathymetry

sst <- accessFVCOM(vars = "SST", years = 2010, months = 6, bounding_box = bb)
plot_mesh(mesh, "SST", values = sst)
} # }