Netcdf 6195 assume longlat

autotest/gdrivers/netcdf.py

@@ -1107,6 +1107,34 @@ def test_netcdf_27():
     gdal.SetConfigOption("GDAL_NETCDF_BOTTOMUP", config_bak)
 
 
+###############################################################################
+# check support for GDAL_NETCDF_ASSUME_LONGLAT configuration option
+
+
+def test_netcdf_assume_longlat():
+
+    # test default config
+    with gdaltest.config_option("GDAL_NETCDF_ASSUME_LONGLAT", "YES"):
+        ds = gdal.Open("data/netcdf/trmm-nc2.nc")
+        srs = ds.GetSpatialRef()
+        assert srs is not None
+        assert srs.ExportToWkt().startswith('GEOGCS["WGS 84')
+    with gdaltest.config_option("GDAL_NETCDF_ASSUME_LONGLAT", "NO"):
+        ds = gdal.Open("data/netcdf/trmm-nc2.nc")
+        assert ds.GetSpatialRef() is None
+
+    # test open option and config overrides
+    with gdaltest.config_option("GDAL_NETCDF_ASSUME_LONGLAT", "YES"):
+        ds = gdal.OpenEx("data/netcdf/trmm-nc2.nc", open_options=["ASSUME_LONGLAT=NO"])
+        srs = ds.GetSpatialRef()
+        assert srs is None
+    with gdaltest.config_option("GDAL_NETCDF_ASSUME_LONGLAT", "NO"):
+        ds = gdal.OpenEx("data/netcdf/trmm-nc2.nc", open_options=["ASSUME_LONGLAT=YES"])
+        srs = ds.GetSpatialRef()
+        assert srs is not None
+        assert srs.ExportToWkt().startswith('GEOGCS["WGS 84')
+
+
 ###############################################################################
 # check support for writing multi-dimensional files (helper function)
 

doc/source/drivers/raster/netcdf.rst

@@ -283,6 +283,12 @@ The following open options are available:
    same dimensions, then they should be reported as multiple bands of a same dataset.
    Default is NO (that is each variable will be reported as a separate
    subdataset)
+
+-  **ASSUME_LONGLAT=[YES/NO]** :  (GDAL >= 3.7) Whether a Geographic CRS should
+    be assumed and applied when, none has otherwise been found, a meaningful 
+    geotransform has been found, and that geotransform is within the bounds 
+    -180,360 -90,90, if YES assume OGC:CRS84. Default is NO.
+
 
 Creation Issues
 ---------------
@@ -510,6 +516,11 @@ Configuration Options
    should be always considered as geospatial axis, even if the lack
    conventional attributes confirming it. Default is NO.
 
+-  **GDAL_NETCDF_ASSUME_LONGLAT=[YES/NO]** :  GDAL >= 3.7) Whether a Geographic CRS should
+    be assumed and applied when, none has otherwise been found, a meaningful 
+    geotransform has been found, and that geotransform is within the bounds 
+    -180,360 -90,90, if YES assume OGC:CRS84. Default is NO.
+
 VSI Virtual File System API support
 -----------------------------------
 

frmts/netcdf/netcdfdataset.cpp

@@ -2873,7 +2873,6 @@ netCDFDataset::netCDFDataset() :
     nYDimID(-1),
     bIsProjected(false),
     bIsGeographic(false),  // Can be not projected, and also not geographic
-
     // State vars.
     bDefineMode(true),
     bAddedGridMappingRef(false),
@@ -4777,6 +4776,49 @@ void netCDFDataset::SetProjectionFromVar( int nGroupId, int nVarId,
     if( !bGotGeogCS && !bGotCfSRS && !bGotGdalSRS && !bGotCfGT && !bGotCfWktSRS)
         CPLDebug("GDAL_netCDF", "did not get projection from CF nor GDAL!");
 
+    // wish of 6195
+    // we don't have CS/SRS, but we do have GT, and we live in -180,360 -90,90
+    if (!bGotGeogCS && !bGotCfSRS && !bGotGdalSRS && !bGotCfWktSRS)  
+    {
+      if (bGotCfGT || bGotGdalGT) 
+      {
+        bool bAssumedLongLat = CPLTestBool(
+          CSLFetchNameValueDef(papszOpenOptions, "ASSUME_LONGLAT",
+                               CPLGetConfigOption("GDAL_NETCDF_ASSUME_LONGLAT", "NO"))); 
+
+        if (bAssumedLongLat && 
+            adfTempGeoTransform[0] >= -180 && adfTempGeoTransform[0] < 360 &&
+            (adfTempGeoTransform[0] + adfTempGeoTransform[1] * poDS->GetRasterXSize()) <= 360 &&
+            adfTempGeoTransform[3] <= 90 && adfTempGeoTransform[3] > -90 &&
+            (adfTempGeoTransform[3] + adfTempGeoTransform[5] * poDS->GetRasterYSize()) >= -90) 
+        {
+
+          poDS->bIsGeographic = true; 
+          char *pszTempProjection = nullptr;
+          // seems odd to use 4326 so OGC:CRS84
+          oSRS.SetFromUserInput("OGC:CRS84");
+          oSRS.exportToWkt(&pszTempProjection);
+          if(returnProjStr != nullptr)
+          {
+            (*returnProjStr) = std::string(pszTempProjection);
+          } 
+          else 
+          {
+            m_bAddedProjectionVarsDefs = true;
+            m_bAddedProjectionVarsData = true;
+            SetSpatialRefNoUpdate(&oSRS);
+          }
+          CPLFree(pszTempProjection);
+
+          CPLDebug("netCDF",
+                   "Assummed Longitude Latitude CRS 'OGC:CRS84' because "
+                   "none otherwise available and geotransform within suitable bounds. "
+                   "Set GDAL_NETCDF_ASSUME_LONGLAT=NO as configuration option or "
+                   "    ASSUME_LONGLAT=NO as open option to bypass this assumption.");
+        }
+      }
+    }
+
     // Search for Well-known GeogCS if got only CF WKT
     // Disabled for now, as a named datum also include control points
     // (see mailing list and bug#4281
@@ -10567,6 +10609,10 @@ void GDALRegister_netCDF()
     "description='Whether 2D variables that share the same indexing dimensions "
     "should be exposed as several bands of a same dataset instead of several "
     "subdatasets.' default='NO'/>"
+"   <Option name='ASSUME_LONGLAT' type='boolean' scope='raster' "
+    "description='Whether when all else has failed for determining a CRS, a "
+    "meaningful geotransform has been found, and is within the  "
+    "bounds -180,360 -90,90, assume OGC:CRS84.' default='NO'/>"
 "</OpenOptionList>" );
 
 

frmts/netcdf/netcdfdataset.h

@@ -90,6 +90,11 @@
 /* Config Options
 
    GDAL_NETCDF_BOTTOMUP=YES/NO overrides bottom-up value on import
+   GDAL_NETCDF_VERIFY_DIMS=[YES/STRICT] : Try to guess which dimensions represent the latitude and longitude only by their attributes (STRICT) or also by guessing the name (YES), default is YES.
+   GDAL_NETCDF_IGNORE_XY_AXIS_NAME_CHECKS=[YES/NO] Whether X/Y dimensions should be always considered as geospatial axis, even if the lack conventional attributes confirming it. Default is NO.
+   GDAL_NETCDF_ASSUME_LONGLAT=[YES/NO] Whether when all else has failed for determining a CRS, a meaningful geotransform has been found, and is within the bounds -180,360 -90,90, if YES assume OGC:CRS84. Default is NO. 
+
+   // TODO: this unusued and a few others occur in the source that are not documented, flush out unused opts and document the rest mdsumner@gmail.com 
    GDAL_NETCDF_CONVERT_LAT_180=YES/NO convert longitude values from ]180,360] to [-180,180]
 */