I. Creating Raster* objects
Raster* objects can be created, from scracth, files, or from objects of other classes, with the following functions:
ll{
raster To create a RasterLayer
stack To create a RasterStack (multiple layers)
brick To create a RasterBrick (multiple layers)
addLayer Add a layer to a Raster* object
dropLayer Remove a layer from a RasterStack or RasterBrick
unstack Create a list of RasterLayer objects from a RasterStack
}
RasterLayer, RasterStack, and RasterBrick objects are, as a group, referred to as Raster* objectsII. Changing the spatial extent and/or resolution of Raster* objects
ll{
merge Combine Raster* objects with different extents (but same origin and resolution)
mosaic Combine RasterLayers with different extents and a function to set values in overlap areas
crop Select a geographic subset of a Raster* object
expand Enlarge a Raster* object
trim Trim a Raster* object by removing exterior rows and/or columns that only have NA values
aggregate Combine cells of a Raster* object to create larger cells
disaggregate Subdivide cells
resample Warp values to a Raster* object with a different origin or resolution
projectRaster Warp values to a Raster* object with a different coordinate reference system
shift Move the location of Raster
flip Flip values horizontally or vertically
rotate Rotate values around the date-line (for lon/lat data)
t Transpose a Raster* object
}III. Raster algebra
ll{
Arith-methods Arith functions (+, -, *, ^, %%, %/%, /)
Math-methods Math functions (abs, sqrt, trunc, log, log10, exp, sin, round among others)
Logic-methods Logic functions (!, &, |)
Summary-methods Summary functions (mean, max, min, range, prod, sum, any, all)
Compare-methods Compare functions (==, !=, >, <, <=",">=)
}IV. Cell based computation
ll{
calc Computations on a single Raster* object
overlay Computations on multiple RasterLayer objects
cover First layer covers second layer except where the first layer is NA
mask Use values from first Raster except where cells of the mask Raster are NA (these become NA)
cut Reclassify values using ranges
subs Reclassify values using a 'is-becomes' matrix
reclass Reclassify using a 'from-to-becomes' matrix
init Initialize cells with new values
stackApply Computations on groups of layers in Raster* object
stackSelect Select cell values from different layers using an index RasterLayer
}V. Spatial contextual computation
ll{
distance Shortest distance to a cell that is not NA
gridDistance Distance when traversing grid cells that are not NA
distanceFromPoints Shortest distance to any point in a set of points
direction Direction (azimuth) to or from cells that are not NA
focal Focal (neighborhood; moving window) functions
edge Edge detection
clump Find clumps (patches)
adjacent Identify cells that are adjacent to a set of cells on a raster
area Compute area of cells (for longitude/latitude data)
terrain Compute slope, aspect and other characteristics from elevation data
Moran Compute global or local Moran or Geary indices of spatial autocorrelation
}VI. Model predictions
ll{
predict Predict a non-spatial model to a RasterLayer
interpolate Predict a spatial model to a RasterLayer
}VII. Data type conversion
ll{
rasterize Rasterizing points, lines or polygons
rasterToPoints Create points from a RasterLayer
rasterToPolygons Create polygons from a RasterLayer
rasterToContour Contour lines from a RasterLayer
rasterFromXYZ RasterLayer from regularly spaces points
rasterFromCells RasterLayer from a Raster object and cell numbers
raster RasterLayer from SpatialGrid*, image, or matrix objects
}
You can coerce Raster* objects to Spatial* objects using as, as in as(object, 'SpatialGridDataFrame')VIII. Summarizing
ll{
cellStats Summarize a Raster cell values with a function
summary Summary of the values of a Raster* object (quartiles and mean)
freq Frequency table of Raster cell values
count Count the frequency of a single (range of) value(s)
crosstab Cross-tabulate two RasterLayer objects, or mulitple layers in a RasterStack/Brick
unique Get the unique values in a Raster* object
zonal Summarize a Raster* object by zones in a RasterLayer
}IX. Accessing values of Raster* object cells
ll{
getValues Get all cell values (fails with very large rasters), or a row of values (safer)
getValuesBlock Get values for a block (a rectangular area defined by start and end row and column
getValuesFocal Get focal values for one or more rows
as.matrix Get cell values as a matrix
as.array Get cell values as an array
extract Extract cell values from a Raster* object (e.g., by cell, coordinates, polygon)
sampleRandom Random sample
sampleRegular Regular sample
minValue Get the minimum value of the cells of a Raster* object (not always known)
maxValue Get the maximum value of the cells of a Raster* object (not always known)
setMinMax Compute the minimum and maximum value of a Raster* object if these are not known
}
You can also use indexing with [ for cell numbers, and [[ for row / column number combinationsX. Plotting
Maps
ll{
plot Plot a Raster* object. The main method to create a map
plotRGB Combine three layers (red, green, blue channels) into a single 'real color' image
spplot Plot a Raster* with the spplot function (sp package)
image Plot a Raster* with the image function
persp Perspective plot of a RasterLayer
contour Contour plot of a RasterLayer
filledContour Filled contour plot of a RasterLayer
text Plot the values of a RasterLayer on top of a map
}
The rasterVis packages has additional plotting methods for Raster objects using methods from the lattice package and from other packages.
Interacting with a map (plot of a RasterLayer)
ll{
zoom Zoom in on a plot of a RasterLayer
click Draw points and/or query values of RasterLayer by clicking on a map
drawPoly Create a SpatialPolygons object by drawing it
drawLine Create a SpatialLines object by drawing it
drawExtent Create an Extent object by drawing it
}
Other plots
ll{
plot x-y scatter plot of values of two RasterLayer objects
hist Histogram of Raster* object values
density Density plot of Raster* object values
pairs Pairs plot for layers in a RasterStack or RasterBrick
boxplot Box plot of the values of one or multiple layers
}XI. Getting and setting Raster* dimensions
Basic parameters of existing Raster* objects can be obtained, and in most cases changed, with:
ll{
ncol The number of columns
nrow The number of rows
ncell The number of cells (can not be set directly, only via ncol or nrow)
res The resolution (x and y)
nlayers How many layers does the object have?
names Get or set the layer names
xres The x resolution (can be set with res)
yres The y resolution (can be set with res)
xmin The minimum x coordinate (or longitude)
xmax The maximum x coordinate (or longitude)
ymin The minimum y coordinate (or latitute)
ymax The maximum y coordinate (or latitute)
extent The extent (minimum and maximum x and y coordinates)
origin The origin of a Raster* object
projection The coordinate reference system (map projection)
isLonLat Test if an object has a longitude/latitude coordinate reference system
filename Filename to which a RasterLayer or RasterBrick is linked
band Band (layer) of a multi-band file that this RasterLayer is linked to
nbands How many bands (layers) does the file have?
compare Compare for equality the basic parameters of two Raster* objects
NAvalue Get or set the NA value (for reading from file; see writeRaster for setting it when writing a file)
}
If there are values associated with a RasterLayer object (either in memory or via a link to a file) these are lost when you change the number of columns or rows or the resolution. This is not the case when the extent is changed (as the number of columns and rows will not be affected). Simlarly, with projection you can set the projection, but this does not transform the data (see projectRaster for that).XII. Computing row, column, cell numbers and coordinates
Cell numbers start at 1 in the upper-left corner. They increase within rows, from left to right, and then row by row from top to bottom. Likewise, row numbers start at 1 at the top of the raster, and column numbrers start at 1 at the left side of the raster.
ll{
xFromCol x-coordinates from column numbers
yFromRow y-coordinates from row numbers
xFromCell x-coordinates from row numbers
yFromCell y-coordinates from cell numbers
xyFromCell x and y coordinates from cell numbers
colFromX Column numbers from x-coordinates (or longitute)
rowFromY Row numbers from y-coordinates (or latitute)
cellFromXY Cell numbers from x and y coordinates
cellFromRowCol Cell numbers from row and column numbers
cellsFromExtent Cell numbers from extent object
coordinates x and y coordinates for all cells
validCell Is this a valid cell number?
validCol Is this a valid column number?
validRow Is this a valid row number?
}XIII. Writing files
Basic writing
ll{
setValues Put new values in a Raster* object
writeRaster Write all values of Raster* object to disk
KML Save raster as KML file
}
Advanced writing of entire files or parts thereof
ll{
blockSize Get suggested block size for reading and writing
writeStart Open a file for writing
writeValues Write some values
writeStop Close the file after writing
update Change the values of an existing file
}XIV. Extent objects
ll{
extent Create an extent object
intersect Intersect two extent objects
union Combine two extent objects
round round/floor/ceiling of the coordinates of an Extent object
alignExtent Align an extent with a Raster* object
drawExtent Create an Extent object by drawing it on top of a map (see plot)
}
You can also use S4 type coercion such as as(extent, 'SpatialPolygons')XVI. Miscellaneous
ll{
getData Download and geographic data
pointDistance Distance between points
readIniFile Read a (windows) 'ini' file
hdr Write header file for a number of raster formats
trim Remove leading and trainling blanks from a character string
extension Get or set the extentsion of a filename
cv Coefficient of variation
modal Modal value
sampleInt Random sample of (possibly very large) range of integer values
showTmpFiles Show temporary files
removeTmpFiles Remove temporary files
}Acknowledgements
Extensive suggestions were made by Jonathan Greenberg, Agustin Lobo, Matteo Mattiuzzi, Steven Mosher, Stefan Schlaffer, and Kevin Ummel. Contributions were also made by Neil Best, Andrew Bevan, Roger Bivand, Isabelle Boulangeat, Lyndon Estes, Josh Gray, Tim Haering, Herry Herry, Paul Hiemstra, Ned Hornig, Mayeul Kauffmann, Rainer Krug, Alice Laborte, John Lewis, Lennon Li, Justin McGrath, Richard Plant, Edzer Pebesma, Oscar Perpinan Lamigueiro, Etienne Racine, David Ramsey, Michael Sumner, Jon Olav Skoien, Shaun Walbridge, Julian Zeidler, and many others.