r.out.gdal: Skip nodata and range checks if export is forced (#6170)

* skip nodata and range checks if export is forced and nodata and data type are given by the user

* update documentation

* add tests using pytest

Author: ninsbl

raster/r.out.gdal/main.c

@@ -528,8 +528,11 @@ int main(int argc, char *argv[])
                         ? "DCELL"
                         : (maptype == FCELL_TYPE ? "FCELL" : "??"))));
 
-    /* if GDAL datatype set by user, do checks */
-    if (type->answer) {
+    if (flag_f->answer)
+        G_verbose_message(_("Forcing raster export"));
+
+    /* if GDAL datatype set by user and export not forced, do checks */
+    if (type->answer && !flag_f->answer) {
 
         /* Check if raster data range is outside of the range of
          * given GDAL datatype, not even overlapping */
@@ -575,13 +578,9 @@ int main(int argc, char *argv[])
             }
         }
         if (retval == -1) {
-            if (flag_f->answer)
-                G_warning(_("Forcing raster export"));
-            else
-                G_fatal_error(
-                    _("Raster export aborted. "
-                      "To override data loss check, use the -%c flag"),
-                    flag_f->key);
+            G_fatal_error(_("Raster export aborted. "
+                            "To override data loss check, use the -%c flag"),
+                          flag_f->key);
         }
     }
 
@@ -619,33 +618,34 @@ int main(int argc, char *argv[])
     }
 
     /* exact range and nodata checks for each band */
-    G_message(_("Checking GDAL data type and nodata value..."));
-    for (band = 0; band < ref.nfiles; band++) {
-        if (ref.nfiles > 1) {
-            G_verbose_message(
-                _("Checking options for raster map <%s> (band %d)..."),
-                G_fully_qualified_name(ref.file[band].name,
-                                       ref.file[band].mapset),
-                band + 1);
-        }
+    if (!flag_f->answer || !nodataopt->answer) {
+        G_message(_("Checking GDAL data type and nodata value..."));
+        for (band = 0; band < ref.nfiles; band++) {
+            if (ref.nfiles > 1) {
+                G_verbose_message(
+                    _("Checking options for raster map <%s> (band %d)..."),
+                    G_fully_qualified_name(ref.file[band].name,
+                                           ref.file[band].mapset),
+                    band + 1);
+            }
 
-        retval = exact_checks(datatype, ref.file[band].name,
-                              ref.file[band].mapset, &cellhead, maptype,
-                              nodataval, nodataopt->key, default_nodataval);
+            retval = exact_checks(datatype, ref.file[band].name,
+                                  ref.file[band].mapset, &cellhead, maptype,
+                                  nodataval, nodataopt->key, default_nodataval);
 
-        /* nodata value is present in the data to be exported */
-        if (retval == -1) {
-            if (flag_f->answer)
-                G_warning(_("Forcing raster export."));
-            else
+            /* nodata value is present in the data to be exported */
+            if (retval == -1) {
+                if (flag_f->answer)
+                    G_verbose_message(_("Forcing raster export."));
+                else
+                    G_fatal_error(_("Raster export aborted."));
+            }
+            /* data don't fit into range of GDAL datatype */
+            else if (retval == -2) {
                 G_fatal_error(_("Raster export aborted."));
-        }
-        /* data don't fit into range of GDAL datatype */
-        else if (retval == -2) {
-            G_fatal_error(_("Raster export aborted."));
+            }
         }
     }
-
     /* Create dataset for output with target driver or, if needed, with
      * in-memory driver */
     char **papszOptions = NULL;

raster/r.out.gdal/r.out.gdal.html

@@ -94,12 +94,19 @@ <h3>Ranges of GDAL data types</h3>
 available for a given file format, and certain compression methods may
 only be supported for certain data types (depends on vendor and version).
 <!-- e.g. data destined for ESRI software should use COMPRESS=LZW/PACKBITS/DEFLATE ??? -->
-<p>If the export settings are set such that data loss would occur in the output
-file (i.e, due to the particular choice of data type and/or file type), the
-normal behaviour of <em>r.out.gdal</em> in this case would be to issue an error
-message describing the problem and exit without exporting. The <b>-f</b> flag
-allows raster export even if some of the data loss tests are not passed, and
-warnings are issued instead of errors.
+<p>By default, <em>r.out.gdal</em> identifies suitable settings for
+<b>nodata</b> and data <b>type</b>, if not given by the user.
+If however the export settings are set such that data loss would occur
+in the output file (i.e, due to the particular choice of data type and/or
+file type), the normal behaviour of <em>r.out.gdal</em> in this case
+would be to issue an error message describing the problem and exit without
+exporting. However, depending on the size of the data, tests to check for
+data loss may take some time. For performance reasons, these tests can be
+skipped if the <b>-f</b>b> flag, the <b>nodata</b>b> option and the
+<b>type</b>b> option are all specified. The assumption here is that the
+user has made a deliberate choice about these settings and considered the
+potential risk of data loss when forcing the export with the <b>-f</b>b>
+flag.
 <p><em>r.out.gdal</em> exports may appear all black or gray on initial
 display in other GIS software. This is not a bug of <em>r.out.gdal</em>,
 but often caused by the default color table assigned by that software.

raster/r.out.gdal/r.out.gdal.md

@@ -99,12 +99,18 @@ Some software may not recognize all of the compression methods available
 for a given file format, and certain compression methods may only be
 supported for certain data types (depends on vendor and version).
 
-If the export settings are set such that data loss would occur in the
-output file (i.e, due to the particular choice of data type and/or file
-type), the normal behaviour of *r.out.gdal* in this case would be to
-issue an error message describing the problem and exit without
-exporting. The **-f** flag allows raster export even if some of the data
-loss tests are not passed, and warnings are issued instead of errors.
+By default, *r.out.gdal* identifies suitable settings for
+**nodata** and data **type**, if not given by the user.
+If however the export settings are set such that data loss would occur
+in the output file (i.e, due to the particular choice of data type and/or
+file type), the normal behaviour of *r.out.gdal* in this case would be
+to issue an error message describing the problem and exit without
+exporting. However, depending on the data size, data loss tests may take
+some time. For performance reasons, those tests can therefore be skipped
+if both the **-f** flag, the **nodata** option and the **type**
+option are given. Here the assumtion is that the user has made a
+deliberate choice about those settings and considered the potential risk
+for data loss when forcing the export with the **-f** flag.
 
 *r.out.gdal* exports may appear all black or gray on initial display in
 other GIS software. This is not a bug of *r.out.gdal*, but often caused

raster/r.out.gdal/tests/test_r_out_gdal.py

@@ -0,0 +1,107 @@
+import grass.script as gs
+import pytest
+from grass.tools import Tools
+
+FORMAT_DICT = {
+    "COG": "tif",
+    "GPKG": "gpkg",
+    "GTiff": "tif",
+    "VRT": "vrt",
+    "netCDF": "nc",
+    "ENVI": "img",
+}
+
+
+@pytest.fixture(scope="module")
+def simple_raster_map(tmp_path_factory):
+    """Fixture to create a basic GRASS environment with a simple raster map containing attributes.
+
+    Set up a temporary GRASS project and region and create a raster map
+    using r.mapcalc.
+
+    Yields:
+        tuple: (map name, GRASS session handle, tmp_path)
+
+    """
+    tmp_path = tmp_path_factory.mktemp("r_out_gdal_project")
+    project = tmp_path / "grassdata"
+    gs.create_project(project, epsg=4326)
+
+    with gs.setup.init(project) as session:
+        tools = Tools(session=session, consistent_return_value=True)
+        tools.g_region(n=10, s=0, e=10, w=0, res=1)
+
+        tools.r_mapcalc(
+            expression="test_raster=row() * col()",
+        )
+
+        yield "test_raster", session, tmp_path
+
+
+@pytest.mark.parametrize("file_format", list(FORMAT_DICT.keys()))
+def test_basic_cog_export(simple_raster_map, file_format):
+    """Test basic export of various formats using 'r.out.gdal'.
+
+    Verifies:
+    - Export of common format works with defaults.
+    """
+    mapname, session, tmp_path = simple_raster_map
+    tools = Tools(session=session, consistent_return_value=True)
+    suffix = FORMAT_DICT[file_format]
+    output_file = tmp_path / f"{mapname}_{file_format}.{suffix}"
+    export = tools.r_out_gdal(
+        input=mapname,
+        output=output_file,
+        format=file_format,
+    )
+    # Check successful export
+    assert output_file.exists(), f"{mapname} not exported to {output_file}"
+    # Check that nodata and data range checks are performed
+    assert "Checking GDAL data type and nodata value" in export.stderr
+
+
+def test_compressed_gtiff_export(simple_raster_map):
+    """Test export of compressed GeoTiff using 'r.out.gdal'.
+
+    Verifies:
+    - Export of common format works.
+    """
+    mapname, session, tmp_path = simple_raster_map
+    tools = Tools(session=session, consistent_return_value=True)
+
+    output_file = tmp_path / f"{mapname}_lzw.tif"
+    export = tools.r_out_gdal(
+        input=mapname,
+        output=output_file,
+        format="GTiff",
+        createopt="COMPRESS=LZW",
+    )
+    # Check successful export
+    assert output_file.exists(), f"{mapname} not exported to {output_file}"
+    # Check that nodata and data range checks are performed
+    assert "Checking GDAL data type and nodata value" in export.stderr
+
+
+def test_fast_gtiff_export(simple_raster_map):
+    """Test fast export of compressed GeoTiff using 'r.out.gdal'.
+
+    Verifies:
+    - Fast export of works if type, nodata and -f are given.
+    """
+    mapname, session, tmp_path = simple_raster_map
+    tools = Tools(session=session, consistent_return_value=True)
+
+    output_file = tmp_path / f"{mapname}_fast.tif"
+    export = tools.r_out_gdal(
+        flags="f",
+        input=mapname,
+        output=output_file,
+        format="GTiff",
+        type="Byte",
+        nodata=255,
+        createopt="COMPRESS=LZW",
+    )
+    # Check successful export
+    assert output_file.exists(), f"{mapname} not exported to {output_file}"
+    # Check that nodata and data range checks are NOT performed
+    assert "Checking GDAL data type and nodata value" not in export.stderr