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View several layers in one page

Source: R/view-list.R
view-layers.Rd

view() of a list draws each element as one or more layers of a single scene, in one view CRS, in list order: the first element at the bottom. view_add() adds a layer to a view already made, on top, and writes a new page, or, for a served view (see Transport in view()), serves the new scene on the same server, at the same URL. An embedded view whose local raster tiles pass the threshold with the new layer becomes served (its earlier page stays on disk). view(a) |> view_add(b) gives the same scene as view(list(a = a, b = b)) when the two have the same view CRS, that is when view_crs(a) equals view_crs(list(a, b)), as it does whenever a is projected, or a and b are both lon/lat south of 40S (or both north of 60N). Otherwise they differ: view_add() keeps a's view CRS, while the list's CRS is chosen from every element (below). Pass crs = to either form to fix it.

Usage

# S3 method for class 'list'
view(
  x,
  ...,
  crs = NULL,
  name = NULL,
  file = NULL,
  theme = c("auto", "light", "dark"),
  transport = getOption("aobview.transport", "auto")
)

view_add(
  v,
  x,
  ...,
  name = NULL,
  file = NULL,
  theme = NULL,
  transport = getOption("aobview.transport", "auto")
)

Arguments

x

For view(), a list of spatial objects. For view_add(), one spatial object (or a list of them) to add.

...

For view() of a list, nothing (per-layer arguments go to view_add()). For view_add(), the arguments view() or view-terra take for x's class, such as fill or zcol for sf data or palette for a SpatRaster.

crs

The view CRS, as for view(). NULL uses view_crs() of the list.

name

The page title. For a list, defaults to the layer labels joined by commas. For view_add(), the new layer's name, which defaults to the expression passed as x; the page title becomes the view's name and this one, joined by a comma.

file

Path of the HTML file to write. Defaults to a new file in the session's temporary directory. view_add() leaves v's page as it is. Not used by a served view (with a warning).

theme

As for view(). view_add() defaults to v's theme.

transport

As for view(). For view_add(), how the new layers are carried: on a served view, "embed" embeds a new local COG's tiles (the server delivers them as blobs) and "auto" or "serve" serve its file; the view stays served either way.

v

A view from view() or view_add().

Value

A view, as for view().

Details

Elements may be sf or sfc objects and 'terra' SpatRaster or SpatVector objects, in any mix of CRSs. Each is drawn as view() or view-terra draws it on its own, with its default style, and reprojected to the view CRS: vectors with sf::st_transform() (lon/lat edges densified first), rasters by aobcore::cog_plan()'s meshes.

View CRS. crs when given; otherwise view_crs() of the whole list: the CRS of the first element with a projected CRS, or, when every element is in lon/lat, the lon/lat rule applied once to their combined latitude range. view_add() keeps the view's CRS and reprojects x to it; it warns when that puts projected vector data into a geographic view (decision 0004 rules out that per-coordinate transform), and a crs argument to it is an error.

Names. List names become layer labels and, made valid and unique, layer ids. An unnamed element takes the expression that gave it in a call such as view(list(coast, r)), else x[[i]]. When an id is taken, _2, _3, ... is appended.

Initial view. The union of the layers' extents in the view CRS, clipped to the view's domain (aobcore::crs_domain(), carried as the scene's view.bounds, allboa/design decision 0005). The scene's spec version is the highest any of its layers or its view needs.

For a style of your own on one layer, such as colour by attribute (zcol), start with view() of it or add it with view_add(), which take each kind's arguments.

See also

view(), view-terra, view_crs().

Examples

coast <- sf::st_read(system.file("extdata", "coastline_south_40s.geojson",
                                 package = "aobcore"), quiet = TRUE)
stations <- sf::st_sfc(sf::st_point(c(110.53, -66.28)), sf::st_point(c(77.97, -68.58)),
                       crs = "OGC:CRS84")
v <- view(list(coast = coast, stations = stations))
vapply(v$scene$layers, function(l) l$id, "")
#> [1] "coast"    "stations"

v2 <- view_add(view(coast), stations, fill = c(220, 60, 40, 255))
v2$scene$layers[[2]]$fill
#> [1] 220  60  40 255

sites <- sf::st_sf(base = c("Casey", "Davis"), geometry = stations)
v3 <- view_add(view(coast), sites, zcol = "base")
v3$scene$layers[[2]]$fill
#> $column
#> [1] "color"
#> 
sst <- terra::rast(system.file("extdata", "polar_3031.tif", package = "aobcore"))
v3 <- view(list(sst = sst, coast = coast))
v3$scene$view$crs
#> [1] "EPSG:3031"