When subsetting a coverage axis, use original values instead of midpoints; these coords are used to find a record

Author: Tara Drwenski

cdm/core/src/main/java/ucar/nc2/ft2/coverage/CoordAxisHelper.java

@@ -496,8 +496,7 @@ CoverageCoordAxisBuilder subsetByIndex(Range range) throws InvalidRangeException
 
     // subset(int ncoords, double start, double end, double[] values)
     CoverageCoordAxisBuilder builder = new CoverageCoordAxisBuilder(axis);
-    builder.subset(ncoords, axis.getCoordMidpoint(range.first()), axis.getCoordMidpoint(range.last()), resolution,
-        subsetValues);
+    builder.subset(ncoords, axis.getCoord(range.first()), axis.getCoord(range.last()), resolution, subsetValues);
     builder.setRange(range);
     return builder;
   }

cdm/core/src/main/java/ucar/nc2/ft2/coverage/CoverageCoordAxis1D.java

@@ -114,6 +114,25 @@ public boolean isAscending() {
     throw new IllegalStateException("unknown spacing" + spacing);
   }
 
+  public double getCoord(int index) {
+    if (index < 0 || index >= getNcoords()) {
+      throw new IllegalArgumentException("Index out of range=" + index);
+    }
+    loadValuesIfNeeded();
+
+    switch (spacing) {
+      case regularPoint:
+      case regularInterval:
+        return startValue + index * getResolution();
+
+      case irregularPoint:
+      case contiguousInterval:
+      case discontiguousInterval:
+        return values[index];
+    }
+    throw new IllegalStateException("Unknown spacing=" + spacing);
+  }
+
   public double getCoordMidpoint(int index) {
     if (index < 0 || index >= getNcoords())
       throw new IllegalArgumentException("Index out of range=" + index);