Package 'tabularaster'

Title: Tidy Tools for 'Raster' Data
Description: Facilities to work with vector and raster data in efficient repeatable and systematic work flow. Missing functionality in existing packages is included here to allow extraction from raster data with 'simple features' and 'Spatial' types and to make extraction consistent and straightforward. Extract cell numbers from raster data and return the cells as a data frame rather than as lists of matrices or vectors. The functions here allow spatial data to be used without special handling for the format currently in use.
Authors: Michael D. Sumner [aut, cre]
Maintainer: Michael D. Sumner <[email protected]>
License: GPL-3
Version: 0.7.2
Built: 2024-11-05 04:13:12 UTC
Source: https://github.com/hypertidy/tabularaster

Help Index

Convert a Raster to a data frame.

Description

Generate a data frame version of any raster object. Use the arguments 'cell', 'dim', 'split_date' and 'value' to control the columns that are included in the output.

Usage

## S3 method for class 'BasicRaster'
as_tibble(
  x,
  cell = TRUE,
  dim = nlayers(x) > 1L,
  value = TRUE,
  split_date = FALSE,
  xy = FALSE,
  ...
)

Arguments

x

a RasterLayer, RasterStack or RasterBrick
cell

logical to include explicit cell number
dim

logical to include slice index
value

logical to return the values as a column or not
split_date

logical to split date into components
xy

logical to include the x and y centre coordinate of each cell
...

unused

Details

If the raster has only one layer, the slice index is not added. Use 'dim = FALSE' to not include the slice index value.

Value

a data frame (tibble) with columns:

  • cellvalue the actual value of the raster cell

  • cellindex the index of the cell (numbered from 1 to ncell() in the raster way).

Columns cellindex or cellvalue may be omitted if either or both of cell and/or value are FALSE, respectively

Other columns might be included depending on the properties of the raster and the arguments to the function:

  • year,month,day if split_date is TRUE

  • x,y if xy is TRUE

  • dimindex if the input has more than 1 layer and dim is TRUE.

Examples

## basic data frame version of a basic raster
as_tibble(raster::raster(volcano))

## data frame with time column since raster has that set
r <- raster::raster(volcano)
br <- raster::brick(r, r)
as_tibble(raster::setZ(br, Sys.Date() + 1:2), cell = TRUE)

Extract cell numbers from a Raster object.

Description

Provide the 'cellnumbers' capability of raster::extract and friends directly, returning a data frame of query-object identifiers 'object_' and the cell number.

Usage

cellnumbers(x, query, ...)

## Default S3 method:
cellnumbers(x, query, ...)

## S3 method for class 'SpatialLines'
cellnumbers(x, query, ...)

## S3 method for class 'sfc'
cellnumbers(x, query, ...)

## S3 method for class 'sf'
cellnumbers(x, query, ...)

Arguments

x

Raster object
query

Spatial object or matrix of coordinates
...

unused

Details

Raster data is inherently 2-dimensional, with a time or 'level' dimension treated like a layers of these 2D forms. The 'raster' package cell number is counted from 1 at the top-left, across the rows and down. This corresponds the the standard "raster graphics" convention used by 'GDAL' and the 'sp' package, and many other implementations. Note that this is different to the convention used by the graphics::image function.

Currently this function only operates as if the input is a single layer objects, it's not clear if adding an extra level of grouping for layers would be sensible.

Value

a data frame (tibble) with columns

  • object_ - the object ID (what row is it from the spatial object)

  • cell_ - the cell number of the raster

Examples

library(raster)
library(dplyr)
r <- raster(volcano) %>% aggregate(fact = 4)
cellnumbers(r, rasterToContour(r, level = 120))
library(dplyr)

cr <- cut(r,  pretty(values(r)))

suppressWarnings(tt <- cellnumbers(cr, polycano))
library(dplyr)
tt %>% mutate(v = extract(r, cell_)) %>% 
group_by(object_) %>% 
summarize(mean(v)) 
head(pretty(values(r)), -1)

Decimate swiftly and ruthlessly

Description

Reduce the resolution of a raster by ruthless decimation.

Usage

decimate(x, dec = 10)

Arguments

x

raster object (single layer).
dec

decimation factor, raw multiplier for the resolution of the output

Details

This is fast, it's just fast extraction with no care taken for utility purposes when you need to reduce the detail.

Value

raster layer

Examples

library(raster)
plot(decimate(raster(volcano)))
contour(raster(volcano), add = TRUE)

Sea surface temperature data.

Description

A smoothed subset of GHRSST.

Format

A raster created GHRSST data and raster smoothing.

Details

See "data-raw/ghrsst.R" and "data-raw/ghrsst-readme.txt" for details.

sst_regions is a simple polygon region layer to sit over the SST data.

Examples

library(raster)
plot(ghrsst, col = hcl.colors(12, "YlOrRd", rev = TRUE))
plot(sst_regions, add = TRUE, col = NA)
cellnumbers(ghrsst, sst_regions)

Index extent

Description

Extent in index space.

Usage

index_extent(x, ex)

Arguments

x

raster layer
ex

extent

Details

Convert a geographic extent into purely index space.

Value

extent object

Examples

## the index extent is the rows/cols
index_extent(raster::raster(volcano), raster::extent(0, 1, 0, 1))

index_extent(raster::raster(volcano), raster::extent(0, 1, 0, .5))

Optimally interpolated SST in near-native form.

Description

See data-raw/oisst.R in the source repository. The file was avhrr-only-v2.20170729.nc, its extent -180, 180, -90, 90 with dimensions 1440x720 in the usual raster configuration.

Format

A data frame of sst values created from OISST data.

Examples

oisst

The raster volcano as polygons.

Description

See data-raw/rastercano.r in the source repository.

Format

A sp::SpatialPolygonsDataFrame with variables: volcano_elevation.

Examples

exists("polycano")

The raster volcano.

Description

See data-raw/rastercano.r in the source repository.

Format

A raster created from the volcano data.

Examples

library(raster)
plot(rastercano)

Sharkcano, the shark and the volcano.

Description

This is just a free image off the internet. The image was read in and all non-essential items dropped. The dimensions in raster::raster terms is stored in attr(sharkcano, "rasterdim").

Format

A data frame with 117843 rows and 2 variables:

cell_

integer, cell index

byte

integer, byte value of shark image pixels

These are cell values on a grid that is 648x958.

References

This is the small version from here, see script in data-raw/sharkcano.r http://www.freestockphotos.biz/stockphoto/16214 Thanks to @jennybc for pointers on finding free stuff: https://github.com/jennybc/free-photos

Examples

library(raster)
rd <- attr(sharkcano, "rasterdim")
rastershark <- raster(matrix(NA_integer_, rd[1], rd[2]))
rastershark[sharkcano$cell_] <- sharkcano$byte  ## byte, heh
## I present to you, Sharkcano!  (Just wait for the 3D version, Quadshark).
plot(rastercano)
contour(rastershark, add = TRUE, labels = FALSE)
plot(rastershark, col = "black")
## another way
plot(rastercano)
points(xyFromCell(rastershark, sharkcano$cell_), pch = ".")

Tabular tools for raster

Description

Extract and index with raster tidy tools for raster.

Details

Tabularaster includes these main functions.

as_tibble convert raster data to data frame form, with control over output and form of dimension/coordinate columns
cellnumbers extract a data frame of query identifiers and cell,pixel index numbers
decimate fast and loose resizing of a raster to coarser resolution
index_extent build an extent in row column form, as opposed to coordinate value form