For time intervals, use interval midpoint as coordinate value

Author: Tara Drwenski

grib/src/main/java/ucar/nc2/grib/collection/GribIosp.java

@@ -780,12 +780,7 @@ private Array makeLazyTime2Darray(Variable coord, Time2Dinfo info) {
           CoordinateTimeIntv timeIntv = (CoordinateTimeIntv) time2D.getTimeCoordinate(runIdx);
           int timeIdx = 0;
           for (TimeCoordIntvValue tinv : timeIntv.getTimeIntervals()) {
-            data[runIdx * ntimes + timeIdx] = timeUnit.getValue() * tinv.getBounds2() + time2D.getOffset(runIdx); // use
-                                                                                                                  // upper
-                                                                                                                  // bounds
-                                                                                                                  // for
-                                                                                                                  // coord
-                                                                                                                  // value
+            data[runIdx * ntimes + timeIdx] = timeUnit.getValue() * tinv.getCoordValue() + time2D.getOffset(runIdx);
             timeIdx++;
           }
         }
@@ -796,8 +791,7 @@ private Array makeLazyTime2Darray(Variable coord, Time2Dinfo info) {
         for (int runIdx = 0; runIdx < nruns; runIdx++) {
           CoordinateTimeIntv timeIntv = (CoordinateTimeIntv) time2D.getTimeCoordinate(runIdx);
           for (TimeCoordIntvValue tinv : timeIntv.getTimeIntervals()) {
-            data[count++] = timeUnit.getValue() * tinv.getBounds2() + time2D.getOffset(runIdx); // use upper bounds for
-                                                                                                // coord value
+            data[count++] = timeUnit.getValue() * tinv.getCoordValue() + time2D.getOffset(runIdx);
           }
         }
         break;
@@ -910,9 +904,8 @@ private void makeTimeCoordinate1D(NetcdfFile ncfile, Group g, CoordinateTimeIntv
     double[] data = new double[ntimes];
     int count = 0;
 
-    // use upper bounds for coord value
     for (TimeCoordIntvValue tinv : coordTime.getTimeIntervals()) {
-      data[count++] = tinv.getBounds2();
+      data[count++] = tinv.getCoordValue();
     }
     v.setCachedData(Array.factory(DataType.DOUBLE, new int[] {ntimes}, data));
 

grib/src/main/java/ucar/nc2/grib/collection/GribIospBuilder.java

@@ -580,12 +580,7 @@ private Array makeLazyTime2Darray(Variable coord, Time2Dinfo info) {
           CoordinateTimeIntv timeIntv = (CoordinateTimeIntv) time2D.getTimeCoordinate(runIdx);
           int timeIdx = 0;
           for (TimeCoordIntvValue tinv : timeIntv.getTimeIntervals()) {
-            data[runIdx * ntimes + timeIdx] = timeUnit.getValue() * tinv.getBounds2() + time2D.getOffset(runIdx); // use
-            // upper
-            // bounds
-            // for
-            // coord
-            // value
+            data[runIdx * ntimes + timeIdx] = timeUnit.getValue() * tinv.getCoordValue() + time2D.getOffset(runIdx);
             timeIdx++;
           }
         }
@@ -596,8 +591,7 @@ private Array makeLazyTime2Darray(Variable coord, Time2Dinfo info) {
         for (int runIdx = 0; runIdx < nruns; runIdx++) {
           CoordinateTimeIntv timeIntv = (CoordinateTimeIntv) time2D.getTimeCoordinate(runIdx);
           for (TimeCoordIntvValue tinv : timeIntv.getTimeIntervals()) {
-            data[count++] = timeUnit.getValue() * tinv.getBounds2() + time2D.getOffset(runIdx); // use upper bounds for
-            // coord value
+            data[count++] = timeUnit.getValue() * tinv.getCoordValue() + time2D.getOffset(runIdx);
           }
         }
         break;
@@ -715,9 +709,8 @@ private void makeTimeCoordinate1D(Group.Builder g, CoordinateTimeIntv coordTime)
     double[] data = new double[ntimes];
     int count = 0;
 
-    // use upper bounds for coord value
     for (TimeCoordIntvValue tinv : coordTime.getTimeIntervals()) {
-      data[count++] = tinv.getBounds2();
+      data[count++] = tinv.getCoordValue();
     }
     v.setCachedData(Array.factory(DataType.DOUBLE, new int[] {ntimes}, data), false);
 

grib/src/main/java/ucar/nc2/grib/coord/TimeCoordIntvValue.java

@@ -28,6 +28,11 @@ public int getIntervalSize() {
     return Math.abs(b2 - b1);
   }
 
+  public double getCoordValue() {
+    // Choose interval midpoint as the coordinate value
+    return (b1 + b2) / 2.0;
+  }
+
   public TimeCoordIntvValue convertReferenceDate(CalendarDate fromDate, CalendarPeriod fromUnit, CalendarDate toDate,
       CalendarPeriod toUnit) {
     CalendarDate start = fromDate.add(fromUnit.multiply(b1));