tar_terra_tiles {geotargets} | R Documentation |
Split a raster into tiles that can be iterated over with dynamic branching
Description
Creates two targets, a list of extents defining tiles and a downstream
pattern that maps over these extents to create a list of SpatRaster
objects
that can be used with dynamic branching.
Usage
tar_terra_tiles(
name,
raster,
tile_fun,
filetype = geotargets_option_get("gdal.raster.driver"),
gdal = geotargets_option_get("gdal.raster.creation.options"),
...,
packages = targets::tar_option_get("packages"),
library = targets::tar_option_get("library"),
repository = targets::tar_option_get("repository"),
error = targets::tar_option_get("error"),
memory = targets::tar_option_get("memory"),
garbage_collection = targets::tar_option_get("garbage_collection"),
deployment = targets::tar_option_get("deployment"),
priority = targets::tar_option_get("priority"),
resources = targets::tar_option_get("resources"),
storage = targets::tar_option_get("storage"),
retrieval = targets::tar_option_get("retrieval"),
cue = targets::tar_option_get("cue"),
description = targets::tar_option_get("description")
)
Arguments
name |
Symbol, name of the target. A target name must be a valid name
for a symbol in R, and it must not start with a dot. See
targets::tar_target() for more information.
|
raster |
a SpatRaster object to be split into tiles.
|
tile_fun |
a helper function that returns a list of numeric vectors such
as tile_grid() , tile_n() or tile_blocksize specified in one of the
following ways:
A named function, e.g. tile_blocksize or "tile_blocksize" .
An anonymous function, e.g. \(x) tile_grid(x, nrow = 2, ncol = 2) .
|
filetype |
character. File format expressed as GDAL driver names passed
to terra::makeTiles() .
|
gdal |
character. GDAL driver specific datasource creation options
passed to terra::makeTiles() .
|
... |
additional arguments not yet used.
|
packages |
Character vector of packages to load right before
the target runs or the output data is reloaded for
downstream targets. Use tar_option_set() to set packages
globally for all subsequent targets you define.
|
library |
Character vector of library paths to try
when loading packages .
|
repository |
Character of length 1, remote repository for target
storage. Choices:
Note: if repository is not "local" and format is "file"
then the target should create a single output file.
That output file is uploaded to the cloud and tracked for changes
where it exists in the cloud. The local file is deleted after
the target runs.
|
error |
Character of length 1, what to do if the target
stops and throws an error. Options:
-
"stop" : the whole pipeline stops and throws an error.
-
"continue" : the whole pipeline keeps going.
-
"null" : The errored target continues and returns NULL .
The data hash is deliberately wrong so the target is not
up to date for the next run of the pipeline. In addition,
as of targets version 1.8.0.9011, a value of NULL is given
to upstream dependencies with error = "null" if loading fails.
-
"abridge" : any currently running targets keep running,
but no new targets launch after that.
-
"trim" : all currently running targets stay running. A queued
target is allowed to start if:
It is not downstream of the error, and
It is not a sibling branch from the same tar_target() call
(if the error happened in a dynamic branch).
The idea is to avoid starting any new work that the immediate error
impacts. error = "trim" is just like error = "abridge" ,
but it allows potentially healthy regions of the dependency graph
to begin running.
(Visit https://books.ropensci.org/targets/debugging.html
to learn how to debug targets using saved workspaces.)
|
memory |
Character of length 1, memory strategy. Possible values:
-
"auto" (default): equivalent to memory = "transient" in almost
all cases. But to avoid superfluous reads from disk,
memory = "auto" is equivalent to memory = "persistent" for
for non-dynamically-branched targets that other targets
dynamically branch over. For example: if your pipeline has
tar_target(name = y, command = x, pattern = map(x)) ,
then tar_target(name = x, command = f(), memory = "auto")
will use persistent memory in order to avoid rereading all of x
for every branch of y .
-
"transient" : the target gets unloaded
after every new target completes.
Either way, the target gets automatically loaded into memory
whenever another target needs the value.
-
"persistent" : the target stays in memory
until the end of the pipeline (unless storage is "worker" ,
in which case targets unloads the value from memory
right after storing it in order to avoid sending
copious data over a network).
For cloud-based file targets
(e.g. format = "file" with repository = "aws" ),
the memory option applies to the
temporary local copy of the file:
"persistent" means it remains until the end of the pipeline
and is then deleted,
and "transient" means it gets deleted as soon as possible.
The former conserves bandwidth,
and the latter conserves local storage.
|
garbage_collection |
Logical: TRUE to run base::gc()
just before the target runs, in whatever R process it is about to run
(which could be a parallel worker).
FALSE to omit garbage collection.
Numeric values get converted to FALSE .
The garbage_collection option in tar_option_set()
is independent of the
argument of the same name in tar_target() .
|
deployment |
Character of length 1. If deployment is
"main" , then the target will run on the central controlling R process.
Otherwise, if deployment is "worker" and you set up the pipeline
with distributed/parallel computing, then
the target runs on a parallel worker. For more on distributed/parallel
computing in targets , please visit
https://books.ropensci.org/targets/crew.html.
|
priority |
Deprecated on 2025-04-08 (targets version 1.10.1.9013).
targets has moved to a more efficient scheduling algorithm
(https://github.com/ropensci/targets/issues/1458)
which cannot support priorities.
The priority argument of tar_target() no longer has a reliable
effect on execution order.
|
resources |
Object returned by tar_resources()
with optional settings for high-performance computing
functionality, alternative data storage formats,
and other optional capabilities of targets .
See tar_resources() for details.
|
storage |
Character string to control when the output of the target
is saved to storage. Only relevant when using targets
with parallel workers (https://books.ropensci.org/targets/crew.html).
Must be one of the following values:
-
"worker" (default): the worker saves/uploads the value.
-
"main" : the target's return value is sent back to the
host machine and saved/uploaded locally.
-
"none" : targets makes no attempt to save the result
of the target to storage in the location where targets
expects it to be. Saving to storage is the responsibility
of the user. Use with caution.
|
retrieval |
Character string to control when the current target
loads its dependencies into memory before running.
(Here, a "dependency" is another target upstream that the current one
depends on.) Only relevant when using targets
with parallel workers (https://books.ropensci.org/targets/crew.html).
Must be one of the following values:
-
"auto" (default): equivalent to retrieval = "worker" in almost all
cases. But to avoid unnecessary reads from disk, retrieval = "auto"
is equivalent to retrieval = "main" for dynamic branches that
branch over non-dynamic targets. For example: if your pipeline has
tar_target(x, command = f()) , then
tar_target(y, command = x, pattern = map(x), retrieval = "auto")
will use "main" retrieval in order to avoid rereading all of x
for every branch of y .
-
"worker" : the worker loads the target's dependencies.
-
"main" : the target's dependencies are loaded on the host machine
and sent to the worker before the target runs.
-
"none" : targets makes no attempt to load its
dependencies. With retrieval = "none" , loading dependencies
is the responsibility of the user. Use with caution.
|
cue |
An optional object from tar_cue() to customize the
rules that decide whether the target is up to date.
|
description |
Character of length 1, a custom free-form human-readable
text description of the target. Descriptions appear as target labels
in functions like tar_manifest() and tar_visnetwork() ,
and they let you select subsets of targets for the names argument of
functions like tar_make() . For example,
tar_manifest(names = tar_described_as(starts_with("survival model")))
lists all the targets whose descriptions start with the character
string "survival model" .
|
Details
When a raster is too large or too high resolution to work on
in-memory, one possible solution is to iterate over tiles. Raster tiles can
then be operated on one at a time, or possibly in parallel if resources are
available, and then the results can be aggregated. A natural way to do this
in the context of a targets
pipeline is to split the raster into multiple
raster targets with dynamic branching so that downstream targets can be
applied to each branch of the upstream target with the pattern
argument
to tar_terra_rast()
or tar_target()
. tar_terra_tiles()
facilitates
creation of such a dynamically branched target. This workflow isn't
appropriate for operations that aggregate spatially, only pixel-wise
operations (possibly aggregating across multiple layers).
This target factory is useful when a raster is too large or too high
resolution to work on in-memory. It can instead be split into tiles that can
be iterated over using dynamic branching.
Value
a list of two targets: an upstream target that creates a list of
extents and a downstream pattern that maps over these extents to create a
list of SpatRaster objects.
Note
The iteration
argument is unavailable because it is hard-coded to
"list"
, the only option that works currently.
When using the tile_blocksize()
helper function, you may need to set
memory = "transient"
on the upstream target provided to the raster
argument of tar_terra_tiles()
. More details are in the help file for
tile_blocksize()
.
Author(s)
Eric Scott
See Also
tile_n()
, tile_grid()
, tile_blocksize()
, tar_terra_rast()
, tar_terra_vrt()
Examples
# For CRAN. Ensures these examples run under certain conditions.
# To run this locally, run the code inside this if statement
if (Sys.getenv("TAR_LONG_EXAMPLES") == "true") {
targets::tar_dir({
targets::tar_script({
library(targets)
library(geotargets)
library(terra)
list(
tar_target(
my_file,
system.file("ex/elev.tif", package="terra"),
format = "file"
),
tar_terra_rast(
my_map,
terra::rast(my_file)
),
tar_terra_tiles(
name = rast_split,
raster = my_map,
tile_fun = \(x) tile_grid(x, ncol = 2, nrow = 2)
)
)
})
targets::tar_manifest()
})
}
[Package
geotargets version 0.3.0
Index]