View source: R/ebirdst-extent.R
ebirdst_extent | R Documentation |
ebirdst_extent
object are used to subset the eBird Status and Trends data
spatially and temporally. This function constructs these objects.
ebirdst_extent(x, t, ...) ## S3 method for class 'bbox' ebirdst_extent(x, t, ...) ## S3 method for class 'numeric' ebirdst_extent(x, t, crs = 4326, ...) ## S3 method for class 'sfc' ebirdst_extent(x, t, ...) ## S3 method for class 'sf' ebirdst_extent(x, t, ...)
x |
the spatial extent; either a rectangular bounding box (defined as a
vector of numbers representing the coordinates of the boundaries or an
|
t |
the temporal extent; a 2-element vector of the start and end dates of the temporal extent, provided either as dates (Date objects or strings in ISO format "YYYY-MM-DD") or numbers between 0 and 1 representing the fraction of the year. Note that dates can wrap around the year, e.g. 'c("2021-12-01", "2021-01-31") is acceptable. See Details for further explanation of the format of t. Leave the argument blank to include the full year of data. |
... |
Additional arguments used by methods. |
crs |
coordinate reference system, provided as a |
The spatial extent, x
, can be either a rectangular bounding box or
a set of spatial polygons. The bounding box can be defined either as an
st_bbox()
object or by providing the coordinates of the rectangle edges
directly as a named vector with elements xmin, xmax, ymin, and ymax (note
that latitude and longitude correspond to y and x, respectively). In this
latter case, a coordinate reference system must be provided explicitly via
the crs
argument (crs = 4326
is the default and is a short form for
unprojected lat/long coordinates). For a polygon spatial extent, x
should
be either an sf or sfc object (with feature type POLYGON
or
MULTIPOLYGON
) from the sf
package. To import data from a Shapefile or
GeoPackage into this format, use read_sf()
.
The temporal extent defines the start and end dates of the time period.
These are most easily provided as Date objects or date strings in ISO
format ("YYYY-MM-DD"). If dates are defined as strings, the year can be
omitted (i.e. "MM-DD"). Alternatively, dates can be defined in terms of
fractions of the year, e.g. t = c(0.25, 0.5)
would subset to data within
the second quarter of the year. In all cases, dates can wrap around the
year, e.g. c("2021-12-01", "2021-01-31") would subset to data in December
or January.
An ebirdst_extent
object consisting of a list with three elements:
the spatial extent extent
, the temporal extent t
, and type
(either
"bbox" or "polygon").
ebirdst_extent(bbox)
: bounding box created with st_bbox()
ebirdst_extent(numeric)
: bounding box given as edges
ebirdst_extent(sfc)
: polygons as sfc spatial feature column
ebirdst_extent(sf)
: polygons as sf object
# bounding box of the north eastern united stats as a numeric vector bb_vec <- c(xmin = -80, xmax = -70, ymin = 40, ymax = 47) ebirdst_extent(bb_vec) # bbox object bb <- sf::st_bbox(bb_vec, crs = 4326) ebirdst_extent(bb) # polygon imported from a shapefile poly <- sf::read_sf(system.file("shape/nc.shp", package="sf")) ebirdst_extent(poly) # subset to january ebirdst_extent(bb, t = c("2021-01-01", "2021-01-31")) # dates can wrap around, e.g. to use dec-jan ebirdst_extent(bb, t = c("2021-12-01", "2021-01-31")) # dates can also be given without an associated year ebirdst_extent(bb, t = c("12-01", "01-31"))
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