spex

Description

Tools for spatial extents that are agnostic regarding format (i.e. sp, sf, or raster). These functions fill some of the gaps within and between these packages for dealing with object extents in flexible ways. Generally, spex considers extents of raster cells, and extents of objects as first-class objects (with projection metadata). and provides helpers for latitudinal boundaries within projected data.

Spatial Extent

Atomic vector extent

Description

Coerce a extent to an atomic vector of c(xmin(x), xmax(x), ymin(x), ymax(x)).

Usage

as_double(x, ...)

## S3 method for class 'Extent'
as_double(x, ...)

as_integer(x, ...)

## S3 method for class 'Extent'
as_integer(x, ...)

Arguments

Details

Note that as_integer results in truncation, see rasterOps for positive buffering.

Value

numeric vector

See Also

base::as.double

Whole grain buffers

Description

Ensure a raster extent aligns to a clean divisor.

Usage

buffer_extent(e1, e2)

Arguments

Details

This function is used to generate extents that have tidy boundaries, i.e. extents that align to a clean whole number like "10000".

(We can't use the S4 group generic because raster has set that specifically for use with '+' and '-'.)

Examples

library(raster)
buffer_extent(extent(0.1, 2.2, 0, 3), 2)

p <- par(xpd = NA) 
plot(lux)
plot(extent(lux), lty = 2, add = TRUE, col = "grey")
plot(buffer_extent(lux, 0.1), add = TRUE)
abline(v = c(5.7, 6.6), h = c(49.4, 50.2))
title("boundaries on clean alignment to 0.1")
par(p)

Extent of simple features

Description

This is the simplest of the missing "raster support" for the sf package, here using the xmin, xmax, ymin, ymax convention used by raster rather than the transpose version favoured in sp and sf.

Usage

extent_sf(x, ...)

Arguments

A raster data set with southern ocean sea ice concentration

Description

When first created this data set was from 2018-04-28.

Latitude circle

Description

Create a circular polygon using a latitude value in a map projection. The longitude range can be modified from global to give a portion of a circle.

Usage

latitudecircle(
  latitude = 0,
  crs = "+proj=stere +lon_0=0 +lat_0=-90 +lat_ts=-71 +ellps=WGS84",
  lonlim = c(-180, 180),
  nverts = 1800
)

Arguments

Details

The argument nverts controls the total number of vertices of the circle within a linearly within the lonlim range of longitudes at latitude

This is for use on classic polar projections centred on the north or the south pole, particularly Polar Stereographic and Lambert Azimuthal Equal Area but will also work with some caveats on other families and situations. We have not explored this more general use. Feel free to contact the maintainer if you have interest in less typical usage or find problems.

Value

SpatialPolygonsDataFrame

Examples

latitudecircle(seq(0, -65, by = -5))
library(raster)
plot(ice)
circ <- latitudecircle(-71, crs = projection(ice))
plot(circ, add = TRUE)

Latitude mask for polar raster

Description

Mask out values based on latitude for a raster. This works by finding all cells at latitudes less than latitude and setting them to missing. If southern = FALSE the inequality is reversed, and all cells at latitudes greater than latitude are masked out.

Usage

latmask(x, latitude = 0, southern = TRUE, trim = FALSE, ...)

Arguments

Details

The trim option allows for the result to be reduced to the common bounding box within which any row or column has a non-missing value.

Value

RasterLayer

See Also

raster::trim, latitudecircle

Examples

 
library(raster)
plot(latmask(ice, -60))
plot(latmask(ice, -60, trim = TRUE))
ice[!ice > 0] <- NA
plot(ice)
plot(latmask(ice, -55, trim = TRUE))

The 'lux' Spatial Polygons from the 'raster' package.

Description

The 'lux' Spatial Polygons from the 'raster' package.

Format

SpatialPolygonsDataFrame-class with columns:

• ID_1

• NAME_1

• ID_2

• NAME_2

• AREA

Examples

library(sp)
plot(lux)

Create a polygon layer from a raster.

Description

This method uses the quadmesh to generate the coordinates, and creates a simple features layer. It's faster by turning off the checking done in the simple features package, but it's also faster than raster because it uses a dense mesh to generate the coordinates.

Usage

## S3 method for class 'RasterLayer'
polygonize(x, na.rm = TRUE, ...)

polygonize(x, ...)

qm_rasterToPolygons(x, na.rm = TRUE, ...)

## S3 method for class 'RasterStack'
polygonize(x, na.rm = TRUE, ...)

## S3 method for class 'RasterBrick'
polygonize(x, na.rm = TRUE, ...)

qm_rasterToPolygons_sp(x, na.rm = TRUE, ...)

Arguments

Details

If na.rm is TRUE (the default) only cells that are not-NA across all layers are created. An exception to this is the empty raster raster::hasValues(x) is FALSE and all the cells will be turned into polygons - since this is what the whole scene is really for, easily creating polygons from a grid.

Value

simple features POLYGON layer, or SpatialPolygonsDataFrame

Warning

Please don't try this on large rasters (> ~1e5 cells), use quadmesh itself for efficient vector based use of a raster's coordinates. It will work reasonably on largish grids, but you won't want to try plotting them or perform operations on them, simple features is incredibly wasteful for objects like this.

Examples

#library(raadtools)
library(raster)
r <- raster(volcano)
r[sample(ncell(r), 3000)] <- NA
b <- brick(r, r*1.5)
psf <- qm_rasterToPolygons(r, na.rm = TRUE)
#psp <- qm_rasterToPolygons_sp(r)
#pspr <- rasterToPolygons(r)
#library(rbenchmark)
#benchmark(qm_rasterToPolygons(r), qm_rasterToPolygons_sp(r), rasterToPolygons(r), replications = 2)
#                        test replications elapsed relative user.self sys.self user.child sys.child
# 1    qm_rasterToPolygons(r)            2   0.476    1.000     0.476    0.000          0         0
# 2 qm_rasterToPolygons_sp(r)            2   4.012    8.429     3.964    0.048          0         0
# 3       rasterToPolygons(r)            2   2.274    4.777     2.268    0.008          0         0

A polygon data set with sf class.

Description

A polygon data set with sf class.

Polygon extent

Description

Create Spatial Polygons with projection metadata from a 'Spatial Extent'.

Usage

spex(x, crs, byid = FALSE, .id, ..., clipboard = FALSE)

## Default S3 method:
spex(x, crs = NULL, byid = FALSE, .id, ..., clipboard = FALSE)

## S3 method for class 'sf'
spex(x, crs, byid = FALSE, .id, ..., clipboard = FALSE)

## S3 method for class 'sfc'
spex(x, crs, byid = FALSE, .id, ..., clipboard = FALSE)

Arguments

Details

Called with no arguments will return the extent of the current 'par("usr")' setting.

Called with a matrix, list, or data frame it will create an extent from a two columned thing.

Called with clipboard = TRUE and x will be treated as the JSON-ic output of the clipboard copy from leafem (WIP). If x is missing, it will be attempted to be read from the clipboard. Clipboard read cannot work on RStudio Server, so we allow the text value to be passed in. I.e. spex(clipboard = TRUE) will read from the clipboard, spex(tx, clipboard = TRUE) will read from tx with value like '{"_southWest":{"lat":-1.307259612275665,"lng":23.411865234375},"_north...}"'.

This function is to replace a common pattern in spatial packages which is

• create an Extent-class, a bounding box in xmin,xmax,ymin,ymax but without projection metadata

• coerce the Extent to SpatialPolygons

• restore the 'CRS', the "coordinate reference system", i.e. projection metadata

• elevate the object to be a SpatialPolygonsDataFrame-class.

In short, this pattern exists because there is no projection metadata stored with either sp's bbox or raster's Extent-class.

Value

'SpatialPolygonsDataFrame'

Warning

Please note that an extent converted to polygons consists of only four unique coordinates, and so this is not necessarily suited for projection transformations.

See Also

This pattern is displayed in the example code for cover.

Examples

library(raster)
data(lux)
exlux <- spex(lux)

plot(lux)
plot(exlux, add = TRUE)

## put an extent and a CRS together
spex(extent(0, 1, 0, 1), crs = "+proj=laea +ellps=WGS84")

Axis ranges from extent

Description

Functions xlim and ylim return the two-value counterparts of an extent.

Usage

xlim(x, ...)

## Default S3 method:
xlim(x, ...)

ylim(x, ...)

## Default S3 method:
ylim(x, ...)

Arguments

Details

Any projection metadata is dropped since this is a one-dimensional entity.