read_RAST(): implement GDAL-GRASS driver by default (only with terra)

R/rast_link.R

@@ -5,7 +5,8 @@
 read_RAST <- function(
     vname, cat = NULL, NODATA = NULL,
     ignore.stderr = get.ignore.stderrOption(), return_format = "terra",
-    close_OK = return_format == "SGDF", flags = NULL) {
+    use_gdal_grass_driver = TRUE, close_OK = return_format == "SGDF",
+    flags = NULL) {
   if (!is.null(cat)) {
     if (length(vname) != length(cat)) {
       stop("vname and cat not same length")
@@ -18,6 +19,7 @@ read_RAST <- function(
     openedConns <- as.integer(row.names(showConnections()))
   }
   stopifnot(is.logical(ignore.stderr), !is.na(ignore.stderr))
+  stopifnot(is.logical(use_gdal_grass_driver), !is.na(use_gdal_grass_driver))
 
   if (!is.null(NODATA)) {
     if (any(!is.finite(NODATA)) || any(!is.numeric(NODATA))) {
@@ -54,20 +56,23 @@ read_RAST <- function(
     if (!(requireNamespace("terra", quietly = TRUE))) {
       stop("terra required for SpatRaster output")
     }
-    drv <- "RRASTER"
-    fxt <- ".grd"
-    ro <- FALSE
-    o <- execGRASS("r.out.gdal", flags = "l", intern = TRUE)
-    oo <- grep("RRASTER", o)
-    if (length(oo) == 0L) ro <- TRUE
-    if (!ro) {
-      RR <- o[oo]
-      RRs <- strsplit(RR, " ")[[1]]
-      if (length(grep("\\(rw", RRs)) == 0L) ro <- TRUE
-    }
-    if (ro) {
-      drv <- "GTiff"
-      fxt <- ".tif"
+    has_grassraster_drv <- gdal_has_grassraster_driver()
+    if (!has_grassraster_drv || !use_gdal_grass_driver) {
+      drv <- "RRASTER"
+      fxt <- ".grd"
+      ro <- FALSE
+      o <- execGRASS("r.out.gdal", flags = "l", intern = TRUE)
+      oo <- grep("RRASTER", o)
+      if (length(oo) == 0L) ro <- TRUE
+      if (!ro) {
+        RR <- o[oo]
+        RRs <- strsplit(RR, " ")[[1]]
+        if (length(grep("\\(rw", RRs)) == 0L) ro <- TRUE
+      }
+      if (ro) {
+        drv <- "GTiff"
+        fxt <- ".tif"
+      }
     }
     reslist <- vector(mode = "list", length = length(vname))
     names(reslist) <- gsub("@", "_", vname)
@@ -197,22 +202,29 @@ read_RAST <- function(
       } else {
         NODATAi <- NODATA[i]
       }
-      tmplist[[i]] <- tempfile(fileext = fxt)
-      if (is.null(flags)) flags <- c("overwrite", "c", "m")
-      if (!is.null(cat) && cat[i]) flags <- c(flags, "t")
-      if (is.null(typei)) {
-        execGRASS("r.out.gdal",
-          input = vname[i], output = tmplist[[i]],
-          format = drv, nodata = NODATAi, flags = flags,
-          ignore.stderr = ignore.stderr
-        )
+      if (has_grassraster_drv && use_gdal_grass_driver) {
+        args <- list(name = vca[1], type = "raster")
+        if (length(vca) == 2L) args <- c(args, mapset = vca[2])
+        tmplist[[i]] <- do.call(generate_header_path, args)
       } else {
-        execGRASS("r.out.gdal",
-          input = vname[i], output = tmplist[[i]],
-          format = drv, nodata = NODATAi, type = typei, flags = flags,
-          ignore.stderr = ignore.stderr
-        )
+        tmplist[[i]] <- tempfile(fileext = fxt)
+        if (is.null(flags)) flags <- c("overwrite", "c", "m")
+        if (!is.null(cat) && cat[i]) flags <- c(flags, "t")
+        if (is.null(typei)) {
+          execGRASS("r.out.gdal",
+                    input = vname[i], output = tmplist[[i]],
+                    format = drv, nodata = NODATAi, flags = flags,
+                    ignore.stderr = ignore.stderr
+          )
+        } else {
+          execGRASS("r.out.gdal",
+                    input = vname[i], output = tmplist[[i]],
+                    format = drv, nodata = NODATAi, type = typei, flags = flags,
+                    ignore.stderr = ignore.stderr
+          )
+        }
       }
+      # message("Reading ", tmplist[[i]])
       reslist[[i]] <- getMethod("rast", "character")(tmplist[[i]])
     }
     resa <- getMethod("rast", "list")(reslist)

man/readRAST.Rd

@@ -11,7 +11,8 @@ Read GRASS raster files from GRASS into R \pkg{terra} \code{"SpatRaster"} or \pk
 
 \usage{
 read_RAST(vname, cat=NULL, NODATA=NULL, ignore.stderr=get.ignore.stderrOption(),
- return_format="terra", close_OK=return_format=="SGDF", flags=NULL)
+ return_format="terra", use_gdal_grass_driver = TRUE, close_OK=return_format=="SGDF",
+ flags=NULL)
 write_RAST(x, vname, zcol = 1, NODATA=NULL, flags=NULL,
  ignore.stderr = get.ignore.stderrOption(), overwrite=FALSE, verbose=TRUE)
 }
@@ -20,6 +21,7 @@ write_RAST(x, vname, zcol = 1, NODATA=NULL, flags=NULL,
   \item{vname}{A vector of GRASS raster file names in mapsets in the current search path, as set by \dQuote{g.mapsets}; the file names may be given as fully-qualified map names using \dQuote{name@mapset}, in which case only the mapset given in the full path will be searched for the existence of the raster; if more than one raster with the same name is found in mapsets in the current search path, an error will occur, in which case the user should give the fully-qualified map name. If the fully-qualified name is used, \code{@} will be replaced by underscore in the output object.}
   \item{cat}{default NULL; if not NULL, must be a logical vector matching vname, stating which (CELL) rasters to return as factor}
   \item{return_format}{default \code{"terra"}, optionally \code{"SGDF"}}
+  \item{use_gdal_grass_driver}{Default \code{TRUE}. The \href{https://github.com/OSGeo/gdal-grass}{standalone GDAL-GRASS driver} for the raster format will be used if \code{return_format} is \code{"terra"} and if the driver is installed. The advantage is that no intermediate file(s) need to be written from GRASS GIS and subsequently read into R; instead the raster dataset(s) are read directly from the GRASS GIS database.}
   \item{ignore.stderr}{default taking the value set by \code{set.ignore.stderrOption}; can be set to TRUE to silence \code{system()} output to standard error; does not apply on Windows platforms}
   \item{close_OK}{default TRUE - clean up possible open connections used for reading metadata; may be set to FALSE to avoid the side-effect of other user-opened connections being broken}
   \item{x}{A \pkg{terra} \code{"SpatRaster"} or \pkg{sp} \code{"SpatialGridDataFrame"} object}
@@ -91,10 +93,17 @@ if (run) {
 }
 if (run) {
   print(system.time(sqdem <- read_RAST(c("sqdemSP", "elevation"),
-    return_format="terra")))
+                                       return_format="terra",
+                                       use_gdal_grass_driver = FALSE)))
 }
+# install the GDAL-GRASS driver to achieve higher speed:
 if (run) {
-names(sqdem)
+  print(system.time(sqdem <- read_RAST(c("sqdemSP", "elevation"),
+                                       return_format="terra",
+                                       use_gdal_grass_driver = TRUE)))
+}
+if (run) {
+  names(sqdem)
 }
 if (run) {
   sqdem1 <- read_RAST(c("sqdemSP@PERMANENT", "elevation@PERMANENT"))