take a shot at a tar_terra_tiles() function

NAMESPACE

@@ -4,6 +4,7 @@ export(geotargets_option_get)
 export(geotargets_option_set)
 export(tar_terra_rast)
 export(tar_terra_sprc)
+export(tar_terra_tiles)
 export(tar_terra_vect)
 importFrom(rlang,"%||%")
 importFrom(rlang,arg_match0)

R/tar_terra_tiles.R

@@ -0,0 +1,185 @@
+tar_terra_tiles_raw <- function(
+        name,
+        raster,
+        template, #E.g. terra::rast(ncols = 3, nrows = 3)
+        tiles_dir, #dir to save tiles to disk.  Can't be inside _targets/ store
+        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"),
+        iteration = targets::tar_option_get("iteration"),
+        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")
+) {
+    targets::tar_assert_chr(name, "name must be a character.")
+    targets::tar_assert_scalar(name, "name must have length 1.")
+    filetype <- filetype %||% "GTiff"
+    gdal <- gdal %||% character(0)
+    name_tiles <- paste0(name, "_tile")
+
+    #Upstream target splits raster into tiles and returns vector of filenames
+
+    #FIXME the upstream target isn't working with the error "cannot branch over empty target (rast_split_tile)" (that's `name_tiles` in this example)
+    upstream <- targets::tar_target_raw(
+        name = name_tiles,
+        command = expression(make_tiles(
+            raster = raster,
+            template = template,
+            tiles_dir = tiles_dir,
+            name_tiles = name_tiles,
+            filetype = filetype,
+            gdal = gdal
+        )),
+        pattern = NULL,
+        packages = packages,
+        library = library,
+        format = "file",
+        repository = repository,
+        iteration = iteration,
+        error = error,
+        memory = memory,
+        garbage_collection = garbage_collection,
+        deployment = deployment,
+        priority = priority,
+        resources = resources,
+        storage = storage,
+        retrieval = retrieval,
+        cue = targets::tar_cue(mode = "always"),
+        description = description
+    )
+
+    #downstream target reads those files in as SpatRaster objects
+    name_tiles_sym <- as.symbol(name_tiles)
+
+    downstream <- targets::tar_target_raw(
+        name = name,
+        command = as.expression(tarchetypes:::call_function("terra::rast", name_tiles_sym)),
+        pattern = as.expression(tarchetypes:::call_function("map", list(name_tiles_sym))),
+        packages = packages,
+        library = library,
+        format = targets::tar_format(
+            read = function(path) terra::rast(path),
+            write = function(object, path) {
+                terra::writeRaster(
+                    object,
+                    path,
+                    filetype = Sys.getenv("GEOTARGETS_GDAL_RASTER_DRIVER"),
+                    overwrite = TRUE,
+                    gdal = strsplit(
+                        Sys.getenv("GEOTARGETS_GDAL_RASTER_CREATION_OPTIONS",
+                                   unset = ";"),
+                        ";")[[1]]
+                )
+            },
+            marshal = function(object) terra::wrap(object),
+            unmarshal = function(object) terra::unwrap(object)
+        ),
+        repository = repository,
+        iteration = "list", #only list works (for now at least)
+        error = error,
+        memory = memory,
+        garbage_collection = garbage_collection,
+        deployment = "main",
+        priority = priority,
+        resources = utils::modifyList(
+            targets::tar_resources(
+                custom_format = targets::tar_resources_custom_format(
+                    #these envvars are used in write function of format
+                    envvars = c(
+                        "GEOTARGETS_GDAL_RASTER_DRIVER" = filetype,
+                        "GEOTARGETS_GDAL_RASTER_CREATION_OPTIONS" = (
+                            paste0(gdal, collapse = ";")
+                        )
+                    )
+                )
+            ), resources),,
+        storage = "main",
+        retrieval = "main",
+        cue = cue,
+        description = description
+    )
+    out <- list(upstream, downstream)
+    names(out) <- c(name_tiles, name)
+    out
+}
+
+#' @export
+tar_terra_tiles <- function(
+        name,
+        raster,
+        template, #E.g. terra::rast(ncols = 3, nrows = 3)
+        tiles_dir, #dir to save tiles to disk.  Can't be inside _targets/ store
+        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"),
+        iteration = targets::tar_option_get("iteration"),
+        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")
+) {
+    name <- targets::tar_deparse_language(substitute(name))
+    tar_terra_tiles_raw(
+        name = name,
+        raster = raster,
+        template = template, #E.g. terra::rast(ncols = 3, nrows = 3)
+        tiles_dir = tiles_dir, #dir to save tiles to disk.  Can't be inside _targets/ store
+        filetype = filetype,
+        gdal = gdal,
+        ...,
+        packages = packages,
+        library = library,
+        repository = repository,
+        iteration = iteration,
+        error = error,
+        memory = memory,
+        garbage_collection = garbage_collection,
+        deployment = deployment,
+        priority = priority,
+        resources = resources,
+        storage = storage,
+        retrieval = retrieval,
+        cue = cue,
+        description = description
+    )
+}
+
+make_tiles <- function(raster, template, tiles_dir, name_tiles, filetype, gdal) {
+    terra::ext(template) <- terra::ext(raster)
+    fs::dir_create(tiles_dir) #TODO use base R?
+    terra::makeTiles(
+        raster,
+        template,
+        filename = fs::path(tiles_dir, name_tiles),
+        overwrite = TRUE,
+        filetype = filetype,
+        gdal = gdal
+    )
+}
+## This works! Why doesn't the upstream target work?
+# raster <- terra::rast(system.file("ex/elev.tif", package="terra"))
+# template <- terra::rast(ncols = 2, nrows = 2)
+# tiles_dir<- "my_tiles"
+# name_tiles <- "myrast_tile"
+# filetype <- "GTiff"
+# gdal <- ""
+# make_tiles(raster, template, tiles_dir, name_tiles, filetype, gdal)