Unscale false_easting/false_northing when writing Coverage

cdm-test/src/test/java/ucar/nc2/dt/grid/TestCFWriter2.java

@@ -1,37 +1,41 @@
 /*
- * Copyright (c) 1998-2018 University Corporation for Atmospheric Research/Unidata
+ * Copyright (c) 1998-2025 University Corporation for Atmospheric Research/Unidata
  * See LICENSE for license information.
  */
 
 package ucar.nc2.dt.grid;
 
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
 import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.experimental.categories.Category;
 import org.junit.rules.TemporaryFolder;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import ucar.nc2.Attribute;
 import ucar.nc2.NetcdfFile;
 import ucar.nc2.NetcdfFileWriter;
 import ucar.nc2.NetcdfFiles;
 import ucar.nc2.Variable;
+import ucar.nc2.constants.CF;
 import ucar.nc2.grib.collection.Grib;
 import ucar.nc2.time.CalendarDate;
 import ucar.nc2.time.CalendarDateRange;
 import ucar.nc2.util.DebugFlagsImpl;
 import ucar.unidata.geoloc.LatLonPoint;
 import ucar.unidata.geoloc.LatLonRect;
 import ucar.unidata.geoloc.ProjectionPoint;
-import ucar.unidata.geoloc.ProjectionPointImpl;
 import ucar.unidata.geoloc.ProjectionRect;
 import ucar.unidata.util.test.category.NeedsCdmUnitTest;
 import ucar.unidata.util.test.TestDir;
 import java.lang.invoke.MethodHandles;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
-import static org.junit.Assert.assertTrue;
 
 /**
  * Test CFGridWriter2
@@ -256,6 +260,51 @@ private void testFileSize(String fileIn, String gridNames, String startDate, Str
     }
   }
 
+  @Test
+  @Category(NeedsCdmUnitTest.class)
+  public void testAxisProjUnitMismatch() throws Exception {
+    String fileOut = tempFolder.newFile().getAbsolutePath();
+    String varName = "HNW";
+
+    final double falseEastingMeters = 400000.0;
+    final double falseEastingKm = falseEastingMeters / 1000;
+
+    try (GridDataset gds = GridDataset.open(TestDir.cdmUnitTestDir + "ncss/test/falseEastingNorthingScaleReset.nc4")) {
+      Variable x = gds.getNetcdfFile().findVariable("x");
+      assertNotNull(x);
+      Attribute xUnits = x.findAttribute(CF.UNITS);
+      assertNotNull(xUnits);
+      assertThat(xUnits.getStringValue()).isEqualTo("m");
+
+      Variable proj = gds.getNetcdfFile().findVariable("lambert_conformal_conic");
+      assertNotNull(proj);
+      Attribute feAttr = proj.findAttribute(CF.FALSE_EASTING);
+      assertNotNull(feAttr);
+      // false_easting in meters
+      assertThat(feAttr.getNumericValue()).isEqualTo(falseEastingMeters);
+
+      // setup subset
+      List<String> gridList = new ArrayList<>();
+      gridList.add(varName);
+
+      NetcdfFileWriter writer = NetcdfFileWriter.createNew(NetcdfFileWriter.Version.netcdf3, fileOut);
 
+      // write subset
+      CFGridWriter2.writeFile(gds, gridList, null, null, 1, null, null, 1, true, writer);
+    }
 
+    try (NetcdfFile ncf = NetcdfFiles.open(fileOut)) {
+      Variable proj = ncf.findVariable("lambert_conformal_conic");
+      assertNotNull(proj);
+      Attribute feAttr = proj.findAttribute(CF.FALSE_EASTING);
+      assertNotNull(feAttr);
+      // GeoX in km
+      Variable x = ncf.findVariable("x");
+      Attribute xUnits = x.findAttribute(CF.UNITS);
+      assertNotNull(xUnits);
+      assertThat(xUnits.getStringValue()).isEqualTo("km");
+      // false_easting in km
+      assertThat(feAttr.getNumericValue()).isEqualTo(falseEastingKm);
+    }
+  }
 }

cdm/core/src/main/java/ucar/nc2/ft2/coverage/writer/CFGridCoverageWriter.java

@@ -1,7 +1,8 @@
 /*
- * Copyright (c) 1998-2020 John Caron and University Corporation for Atmospheric Research/Unidata
+ * Copyright (c) 1998-2025 John Caron and University Corporation for Atmospheric Research/Unidata
  * See LICENSE for license information.
  */
+
 package ucar.nc2.ft2.coverage.writer;
 
 import com.google.common.base.Preconditions;
@@ -13,13 +14,15 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.stream.Collectors;
 import javax.annotation.Nullable;
 import ucar.ma2.Array;
 import ucar.ma2.DataType;
 import ucar.ma2.InvalidRangeException;
 import ucar.ma2.Section;
 import ucar.nc2.Attribute;
 import ucar.nc2.AttributeContainer;
+import ucar.nc2.AttributeContainerMutable;
 import ucar.nc2.Dimension;
 import ucar.nc2.Group;
 import ucar.nc2.Variable;
@@ -28,6 +31,7 @@
 import ucar.nc2.constants.CDM;
 import ucar.nc2.constants.CF;
 import ucar.nc2.constants._Coordinate;
+import ucar.nc2.dataset.transform.AbstractTransformBuilder;
 import ucar.nc2.ft2.coverage.Coverage;
 import ucar.nc2.ft2.coverage.CoverageCollection;
 import ucar.nc2.ft2.coverage.CoverageCoordAxis;
@@ -308,8 +312,53 @@ private void addCoordTransforms(CoverageCollection subsetDataset, Group.Builder
       // scalar coordinate transform variable - container for transform info
       Variable.Builder ctv = Variable.builder().setName(ct.getName()).setDataType(DataType.INT);
       group.addVariable(ctv);
-      ctv.addAttributes(ct.attributes());
+      AttributeContainer ctAttrs = ct.attributes();
+
+      AttributeContainerMutable newAttrs = AttributeContainerMutable.copyFrom(ctAttrs);
+      // adjust false_easting/false_northing if needed
+      // possibly needed if the subset dataset includes GeoX or GeoY axes, so first find those
+      Map<AxisType, CoverageCoordAxis> mapCoordAxes = subsetDataset.getCoordAxes().stream()
+          .filter(ca -> ca.getAxisType() == AxisType.GeoX || ca.getAxisType() == AxisType.GeoY)
+          .collect(Collectors.toMap(CoverageCoordAxis::getAxisType, mca -> mca));
+      // if we found GeoX and/or GeoY axes, start checking
+      if (!mapCoordAxes.isEmpty()) {
+        boolean eastScaled = false;
+        if (mapCoordAxes.containsKey(AxisType.GeoX)) {
+          eastScaled = scaleFalseEastingNorthing(CF.FALSE_EASTING, ctAttrs, newAttrs,
+              mapCoordAxes.get(AxisType.GeoX).attributes().findAttributeString(CF.UNITS, null));
+        }
+        boolean northScaled = false;
+        if (mapCoordAxes.containsKey(AxisType.GeoY)) {
+          northScaled = scaleFalseEastingNorthing(CF.FALSE_NORTHING, ctAttrs, newAttrs,
+              mapCoordAxes.get(AxisType.GeoY).attributes().findAttributeString(CF.UNITS, null));
+        }
+        // do not propagate the unit attribute on the projection variable if we ensured the
+        // units match, as this is state matchs CF (likely this attribute was added when creating
+        // a coverage from the NetcdfDataset.
+        if (!ctAttrs.findAttributeString(CF.UNITS, "").isEmpty()) {
+          if (eastScaled || northScaled) {
+            newAttrs.removeAttribute(CF.UNITS);
+          }
+        }
+      }
+      ctv.addAttributes(newAttrs.toImmutable());
+    }
+  }
+
+  private boolean scaleFalseEastingNorthing(String falseValueType, AttributeContainer cta,
+      AttributeContainerMutable newCta, String caUnits) {
+    double falseValue = cta.findAttributeDouble(falseValueType, Double.MIN_VALUE);
+    boolean scaled = false;
+    if (falseValue != Double.MIN_VALUE) {
+      double scalef = AbstractTransformBuilder.getFalseEastingScaleFactor(caUnits);
+      if (scalef != 1.0) {
+        scaled = true;
+        newCta.removeAttribute(falseValueType);
+        // here we divide by scalef, to undo the scalef applied when creating the Coverage
+        newCta.addAttribute(Attribute.builder(falseValueType).setNumericValue(falseValue / scalef, false).build());
+      }
     }
+    return scaled;
   }
 
   private void addLatLon2D(CoverageCollection subsetDataset, Group.Builder group) {

cdm/core/src/test/java/ucar/nc2/ft2/coverage/writer/TestCFGridCoverageWriter.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2025 University Corporation for Atmospheric Research/Unidata
+ * See LICENSE for license information.
+ */
+
+package ucar.nc2.ft2.coverage.writer;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertNotNull;
+
+import java.io.IOException;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.junit.rules.TemporaryFolder;
+import ucar.ma2.InvalidRangeException;
+import ucar.nc2.Attribute;
+import ucar.nc2.NetcdfFile;
+import ucar.nc2.NetcdfFiles;
+import ucar.nc2.Variable;
+import ucar.nc2.constants.CF;
+import ucar.nc2.constants.FeatureType;
+import ucar.nc2.ft2.coverage.CoverageCollection;
+import ucar.nc2.ft2.coverage.CoverageDatasetFactory;
+import ucar.nc2.ft2.coverage.FeatureDatasetCoverage;
+import ucar.nc2.write.NetcdfFileFormat;
+import ucar.nc2.write.NetcdfFormatWriter;
+import ucar.unidata.util.test.TestDir;
+import ucar.unidata.util.test.category.NeedsCdmUnitTest;
+
+public class TestCFGridCoverageWriter {
+
+  @Rule
+  public final TemporaryFolder tempFolder = new TemporaryFolder();
+
+  @Test
+  @Category(NeedsCdmUnitTest.class)
+  public void testCFGridCoverageWriterNonKmProjectionParams() throws IOException, InvalidRangeException {
+    String fileOut = tempFolder.newFile().getAbsolutePath();
+    String fileIn = TestDir.cdmUnitTestDir + "ncss/test/falseEastingNorthingScaleReset.nc4";
+
+    try (FeatureDatasetCoverage cc = CoverageDatasetFactory.open(fileIn)) {
+      CoverageCollection gcs = cc.findCoverageDataset(FeatureType.GRID);
+      assertNotNull(gcs);
+      NetcdfFormatWriter.Builder writerb =
+          NetcdfFormatWriter.builder().setNewFile(true).setFormat(NetcdfFileFormat.NETCDF3).setLocation(fileOut);
+
+      CFGridCoverageWriter.Result result = CFGridCoverageWriter.write(gcs, null, null, false, writerb, 0);
+      if (!result.wasWritten()) {
+        throw new InvalidRangeException("Error writing: " + result.getErrorMessage());
+      }
+    }
+
+    try (NetcdfFile ncf = NetcdfFiles.open(fileOut)) {
+      Variable proj = ncf.findVariable("lambert_conformal_conic");
+      assertNotNull(proj);
+      Attribute feAttr = proj.findAttribute(CF.FALSE_EASTING);
+      assertNotNull(feAttr);
+      Attribute fnAttr = proj.findAttribute(CF.FALSE_NORTHING);
+      assertNotNull(fnAttr);
+      // GeoX axis in meters
+      Variable x = ncf.findVariable("x");
+      assertNotNull(x);
+      assertThat(x.getUnitsString()).isEqualTo("m");
+      // false_easting in m
+      assertThat(feAttr.getNumericValue()).isEqualTo(400000.0);
+      assertThat(fnAttr.getNumericValue()).isEqualTo(400000.0);
+      // should not have a units attribute on the proj variable
+      Attribute unitsAttr = proj.findAttribute(CF.UNITS);
+      assertThat(unitsAttr).isNull();
+    }
+  }
+}