Package 'lazyraster'

Convert to in-memory raster

Description

Create an actual raster::raster object by breaking the lazy contract and demanding pixel values at a given resolution.

Usage

as_raster(
  x,
  dim = NULL,
  resample = "NearestNeighbour",
  native = FALSE,
  band = 1L
)

Arguments

x	a lazyraster
dim	dimensions, pixel size in rows and columns
resample	resampling method, see vapour::vapour_read_raster
native	return raster at native resolution, default is FALSE
band	set to 1-based band numbers to return (independently of those set with lazyraster())

Details

Control the dimensions and method for resampling with the 'dim' and 'resample' arguments.

If dim is non-integer it is rounded according to what raster does with the dimensions.

When native = TRUE the dim argument is ignored, and no resampling is performed.

Value

a regular raster 'BasicRaster' in-memory object

---

Lazy raster

Description

A lazyraster is a metadata-only shell around a raster file source. Only metadata is read and and used for extent and resolution logic. A lazyraster may be cropped lazily and if plotted or converted to in-memory raster only a reasonable level-of-detail is actually used.

Usage

lazyraster(gdalsource, band = NULL, sds = NULL, ...)

Arguments

gdalsource	a file name or other source string
band	which band to use, defaults to all present
sds	which subdataset to use, set to 1 if in doubt (see vapour::vapour_sds_names)
...	ignored for now

Details

See crop() for cropping - it works the same but returns a lazyraster, and as_raster() for converting to an in-memory raster.

Value

a lazyraster object, a simple shell around a GDAL raster source

Warning

If the inferred Y extents appear to be reversed (ymax > ymin) then they are reversed, with a warning. This occurs for any GDAL data source that does not have a geotransform and so is required for use with raster. This might not be the right interpretation, geotransforms are very general and it might mean the data is meant to be oriented that way. (I don't know why GDAL sets a positive Y pixel height as the default, it's a bit of a pain - should the data be flipped, or should Y be interpreted negative - no way to know!).

Examples

sstfile <- system.file("extdata/sst.tif", package = "vapour")
lazyraster(sstfile)
## convert to raster (in memory, but not all of the source)
as_raster(lazyraster(sstfile))
## crop and stay as lazyraster
crop(lazyraster(sstfile), raster::extent(142, 143, -50, -45))
## crop and convert to raster
as_raster(crop(lazyraster(sstfile), raster::extent(142, 143, -50, -45)))

---

Lazy raster S3 methods

Description

Print and format for lazyraster.

Plot for lazyraster, data pulled on-demand at a reasonable level-of-detail.

Usage

## S3 method for class 'lazyraster'
print(x, ...)

## S3 method for class 'lazyraster'
format(x, ...)

## S3 method for class 'lazyraster'
plot(x, y, ...)

Arguments

x	a lazyraster
...	passed to raster::plot
y	ignored

Details

Data is pulled from the GDAL source at a resolution suited for the currently open graphics device.

Examples

fl <- system.file("images/ga_srtm.png", package = "lazyraster")
print(lazyraster(fl))
## won't work with dumb images with gdalwarp, need rethink
#plot(lazyraster(fl))

---

Raster methods (S4) for lazyraster.

Description

These methods are generics from the raster package, extended to work for lazyrasters.

Usage

## S4 method for signature 'lazyraster'
crop(x, y, ...)

Arguments

x	various (raster, extent)
y	an object with extent (for crop)
...	arguments passed to underlying raster function

Details

For crop() this set an active window of data using the same crop() function as the raster package. This is the data window that will be pulled by conversion to an actual raster by as_raster().

Value

lazyraster() and crop() return a lazyraster object, extent() returns a regular raster extent

See Also

raster::raster(), raster::extent(), raster::crop()

Examples

sstfile <- system.file("extdata/sst.tif", package = "vapour")
lr <- lazyraster(sstfile)
## crop and stay as lazyraster
crop(lazyraster(sstfile), raster::extent(142, 143, -50, -45))

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Mercator extent

Description

Create an extent in Mercator projection from a longitude, latitude, and a width,height.

Usage

merc(x = 146.7, y = -42, wh = 256000)

Arguments

x	longitude
y	latitude
wh	width and height, in metres - if only one vaue provided it is also used for height

Value

four values, xmin, xmax, ymin, ymax in global Mercator

Examples

merc()  ## a parochial default
library(lazyraster)
vearth <- '<GDAL_WMS> <Service name="VirtualEarth">
<ServerUrl>http://a${server_num}.ortho.tiles.virtualearth.net/tiles/a${quadkey}.jpeg?g=90</ServerUrl></Service>
<MaxConnections>4</MaxConnections>    <Cache/>    </GDAL_WMS>'
lr <- lazyraster(vearth)
## Not run: \donttest{
raster::plotRGB(as_raster(crop(lr, merc(-90, 52, 256e4)), band = 1:3))
}
## End(Not run)

---

Quadmesh for lazyrasters

Description

Provides a re-exported generic quadmesh and a method for lazyraster.

Usage

## S3 method for class 'lazyraster'
quadmesh(x, z = x, na.rm = FALSE, ..., texture = NULL, texture_filename = NULL)

Arguments

x	raster object for mesh structure
z	raster object for height values
na.rm	remove quads where missing values?
...	arguments passed to as_raster, for both x and z if necessary
texture	optional input RGB raster, 3-layers
texture_filename	optional input file path for PNG texture

Details

A quadmesh is a 'rgl::mesh3d' extension, and can be plotted in 3D with 'rgl::shade3d'.

Value

a quadmesh, derived from 'rgl::mesh3d'

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