[sis] branch geoapi-4.0 updated: Avoid a rounding error which caused the creation of unnecessary concatenated transforms.

[desruisseaux]

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desruisseaux pushed a commit to branch geoapi-4.0
in repository https://gitbox.apache.org/repos/asf/sis.git


The following commit(s) were added to refs/heads/geoapi-4.0 by this push:
     new edabd5aee9 Avoid a rounding error which caused the creation of 
unnecessary concatenated transforms.
edabd5aee9 is described below

commit edabd5aee986f857dbf77ba9fb134eebdf184a52
Author: Martin Desruisseaux <martin.desruisse...@geomatys.com>
AuthorDate: Mon Jul 11 11:23:20 2022 +0200

    Avoid a rounding error which caused the creation of unnecessary 
concatenated transforms.
---
 .../internal/referencing/WraparoundApplicator.java | 27 +++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git 
a/core/sis-referencing/src/main/java/org/apache/sis/internal/referencing/WraparoundApplicator.java
 
b/core/sis-referencing/src/main/java/org/apache/sis/internal/referencing/WraparoundApplicator.java
index 9f6a5c60d6..943f853273 100644
--- 
a/core/sis-referencing/src/main/java/org/apache/sis/internal/referencing/WraparoundApplicator.java
+++ 
b/core/sis-referencing/src/main/java/org/apache/sis/internal/referencing/WraparoundApplicator.java
@@ -29,6 +29,7 @@ import org.opengis.referencing.operation.TransformException;
 import org.apache.sis.referencing.operation.transform.MathTransforms;
 import org.apache.sis.referencing.operation.transform.WraparoundTransform;
 import org.apache.sis.util.collection.BackingStoreException;
+import org.apache.sis.internal.util.Numerics;
 import org.apache.sis.measure.Longitude;
 import org.apache.sis.measure.Units;
 
@@ -38,7 +39,7 @@ import org.apache.sis.measure.Units;
  * Each {@code WraparoundTransform} instance should be used only once.
  *
  * @author  Martin Desruisseaux (Geomatys)
- * @version 1.2
+ * @version 1.3
  * @since   1.1
  * @module
  */
@@ -165,10 +166,34 @@ public final class WraparoundApplicator {
             // Some `DirectPosition` implementations compute coordinates only 
when first needed.
             throw e.unwrapOrRethrow(TransformException.class);
         }
+        /*
+         * If the two medians are very close to each other, make them equal. 
It simplifies the chain of operations.
+         * This code applies an arbitrary threshold for avoiding the effect of 
rounding errors, because `create(…)`
+         * will use the difference between those two values.
+         */
+        final double max = Math.max(Math.abs(sm), Math.abs(m));
+        if (Math.abs(sm - m) < max * Numerics.COMPARISON_THRESHOLD) {
+            // Arbitrarily take the value closest to an integer.
+            final int n = Math.getExponent(max);
+            if (error(sm, n) <= error(m, n)) {
+                m = sm;
+            } else {
+                sm = m;
+            }
+        }
         final MathTransform wraparound = 
WraparoundTransform.create(tr.getTargetDimensions(), wraparoundDimension, 
period, sm, m);
         return MathTransforms.concatenate(tr, wraparound);
     }
 
+    /**
+     * Returns an arbitrary measurement of the error of given value.
+     * We use this measurement for arbitrarily taking the value closest to an 
integer.
+     */
+    private static double error(double m, final int n) {
+        m = Math.scalb(m, 6 - n);           // 6 is an arbitrary extra 
accuracy to keep for comparison.
+        return Math.abs(m - Math.rint(m));
+    }
+
     /**
      * Returns the range (maximum - minimum) of axis in specified dimension if 
it has wraparound meaning,
      * or {@link Double#NaN} otherwise. This method implements a fallback for 
longitude axis if it does