Only apply enhancements once for CoordinateAxis variables

cdm/core/src/main/java/ucar/nc2/dataset/VariableDS.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998-2018 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.dataset;
@@ -494,9 +494,28 @@ protected Array _read(Section section) throws IOException, InvalidRangeException
   // do not call directly
   @Override
   public Array reallyRead(Variable client, CancelTask cancelTask) throws IOException {
-    if (orgVar == null)
+    if (orgVar == null) {
+      // possible aggregation
+      if (this.proxyReader != null && this.proxyReader instanceof ucar.nc2.ncml.Aggregation) {
+        return this.proxyReader.reallyRead(client, cancelTask);
+      }
       return getMissingDataArray(shape);
+    }
 
+    if (client instanceof CoordinateAxis) {
+      // If orgVar is a VariableDS (orgVar of a CoordinateAxis using the non-builder
+      // API, for example), call reallyRead on it, otherwise, enhancements will get
+      // applied twice in a second _read() call triggered by calling read() on the
+      // VariableDS.
+      if (orgVar instanceof VariableDS && !orgVar.hasCachedData()) {
+        return orgVar.reallyRead(client, cancelTask);
+      }
+      // Some aggregations use a DatasetProxyReader for reading a coordinate axis
+      // variable, so check to see if that's what we have and, if so, use it.
+      if (ucar.nc2.ncml.Aggregation.instanceOfDatasetProxyReader(this.proxyReader)) {
+        return this.proxyReader.reallyRead(client, cancelTask);
+      }
+    }
     return orgVar.read();
   }
 
@@ -508,9 +527,28 @@ public Array reallyRead(Variable client, Section section, CancelTask cancelTask)
     if ((null == section) || section.computeSize() == getSize())
       return reallyRead(client, cancelTask);
 
-    if (orgVar == null)
-      return getMissingDataArray(section.getShape());
+    if (orgVar == null) {
+      // possible aggregation
+      if (this.proxyReader != null && this.proxyReader instanceof ucar.nc2.ncml.Aggregation) {
+        return this.proxyReader.reallyRead(client, section, cancelTask);
+      }
+      return getMissingDataArray(shape);
+    }
 
+    if (client instanceof CoordinateAxis) {
+      // If orgVar is a VariableDS (orgVar of a CoordinateAxis using the non-builder
+      // API, for example), call reallyRead on it, otherwise, enhancements will get
+      // applied twice in a second _read() call triggered by calling read() on the
+      // VariableDS.
+      if (orgVar instanceof VariableDS && !orgVar.hasCachedData()) {
+        return orgVar.reallyRead(client, section, cancelTask);
+      }
+      // Some aggregations use a DatasetProxyReader for reading a coordinate axis
+      // variable, so check to see if that's what we have and, if so, use it.
+      if (ucar.nc2.ncml.Aggregation.instanceOfDatasetProxyReader(this.proxyReader)) {
+        return this.proxyReader.reallyRead(client, section, cancelTask);
+      }
+    }
     return orgVar.read(section);
   }
 

cdm/core/src/main/java/ucar/nc2/ncml/Aggregation.java

@@ -1,5 +1,5 @@
 /*
- * 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.txt for license information.
  */
 package ucar.nc2.ncml;
@@ -777,6 +777,11 @@ protected void setDatasetAcquireProxy(DatasetProxyReader proxy, Group g) throws
     }
   }
 
+  public static boolean instanceOfDatasetProxyReader(Object obj) {
+    if (obj == null)
+      return false;
+    return obj instanceof DatasetProxyReader;
+  }
 
   protected class DatasetProxyReader implements ProxyReader {
     Dataset dataset;

cdm/core/src/test/java/ucar/nc2/dataset/TestScaledCoordAxis1D.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2025 University Corporation for Atmospheric Research/Unidata
+ * See LICENSE.txt for license information.
+ */
+package ucar.nc2.dataset;
+
+import java.io.IOException;
+import java.util.Objects;
+import org.junit.Test;
+import ucar.ma2.Array;
+import ucar.nc2.Attribute;
+import ucar.nc2.NetcdfFile;
+import ucar.nc2.NetcdfFiles;
+import ucar.nc2.Variable;
+import ucar.nc2.constants.AxisType;
+import ucar.unidata.util.test.TestDir;
+import static com.google.common.truth.Truth.assertThat;
+
+public class TestScaledCoordAxis1D {
+
+  @Test
+  public void testEnhancedOnce() throws IOException {
+    String testfile = TestDir.cdmLocalTestDataDir + "scaledCoordAxis1D.nc4";
+    try (NetcdfFile ncf = NetcdfFile.open(testfile, null); NetcdfDataset ncd = NetcdfDataset.openDataset(testfile)) {
+      checkAxis(ncf, ncd, "x", AxisType.GeoX);
+      checkAxis(ncf, ncd, "y", AxisType.GeoY);
+    }
+  }
+
+  @Test
+  public void testEnhancedOnceBuilders() throws IOException {
+    String testfile = TestDir.cdmLocalTestDataDir + "scaledCoordAxis1D.nc4";
+    try (NetcdfFile ncf = NetcdfFiles.open(testfile, null); NetcdfDataset ncd = NetcdfDatasets.openDataset(testfile)) {
+      checkAxis(ncf, ncd, "x", AxisType.GeoX);
+      checkAxis(ncf, ncd, "y", AxisType.GeoY);
+    }
+  }
+
+  public void checkAxis(NetcdfFile ncf, NetcdfDataset ncd, String axisName, AxisType axisType) throws IOException {
+    Variable var = ncf.findVariable(axisName);
+    assertThat(var != null).isTrue();
+    Array vals = var.read();
+    Attribute scaleAttr = var.findAttribute("scale_factor");
+    assertThat(scaleAttr).isNotNull();
+    float scale = Objects.requireNonNull(scaleAttr.getNumericValue()).floatValue();
+    Attribute offsetAttr = var.findAttribute("add_offset");
+    assertThat(offsetAttr).isNotNull();
+    float offset = Objects.requireNonNull(offsetAttr.getNumericValue()).floatValue();
+    assertThat(vals.getShape().length).isEqualTo(1);
+    int len = vals.getShape()[0];
+    final float[] valsEnhanced = new float[len];
+    for (int i = 0; i < len; i++) {
+      valsEnhanced[i] = vals.getShort(i) * scale + offset;
+    }
+    // vals have a scale and offset.
+    assertThat(vals).isNotNull();
+    CoordinateAxis coodAxis = ncd.findCoordinateAxis(axisType);
+    Array coordVals = coodAxis.read();
+    for (int i = 0; i < len; i++) {
+      assertThat(coordVals.getFloat(i)).isWithin(1e-6f).of(valsEnhanced[i]);
+    }
+  }
+}