From 0c8915472975b3123d91d7f3ee6ddb0dbb2c51f1 Mon Sep 17 00:00:00 2001
From: Mark Olesen <Mark.Olesen@esi-group.com>
Date: Thu, 29 Jul 2021 15:43:05 +0200
Subject: [PATCH] ENH: add fallback behaviour for distanceSurface proximity
 regions (#1631)

- using the proximityRegions filter when there is no enclosing surface
  to segregate domains causes a surface of zero-faces to be created.

  In most cases, this means that a simpler proximityFaces filter would
  have been more appropriate. To increase overall robustness, revert
  to the simpler proximityFaces filter logic when the proximityRegions
  would otherwise result in zero faces (globally seen).
---
 .../surface/distanceSurface/distanceSurface.C |  2 ++
 .../distanceSurface/distanceSurfaceFilter.C   | 21 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/sampling/surface/distanceSurface/distanceSurface.C b/src/sampling/surface/distanceSurface/distanceSurface.C
index 3f634f04f9..e2baa1b14c 100644
--- a/src/sampling/surface/distanceSurface/distanceSurface.C
+++ b/src/sampling/surface/distanceSurface/distanceSurface.C
@@ -279,6 +279,7 @@ Foam::distanceSurface::distanceSurface
      || (distance_ < 0)
      || dict.getOrDefault<bool>("signed", true)
     ),
+
     isoParams_
     (
         dict,
@@ -374,6 +375,7 @@ Foam::distanceSurface::distanceSurface
      || (distance_ < 0)
      || useSignedDistance
     ),
+
     isoParams_(params),
     topoFilter_(topologyFilterType::NONE),
     nearestPoints_(),
diff --git a/src/sampling/surface/distanceSurface/distanceSurfaceFilter.C b/src/sampling/surface/distanceSurface/distanceSurfaceFilter.C
index 0ca4e4961b..b3e8779a04 100644
--- a/src/sampling/surface/distanceSurface/distanceSurfaceFilter.C
+++ b/src/sampling/surface/distanceSurface/distanceSurfaceFilter.C
@@ -429,6 +429,27 @@ void Foam::distanceSurface::filterRegionProximity
     }
 
 
+    // If filtering with region proximity results in zero faces,
+    // revert to face-only proximity filter
+    if (returnReduce(acceptFaces.none(), andOp<bool>()))
+    {
+        acceptFaces.reset();
+        prune = false;
+
+        // Consider the absolute proximity of the face centres
+        forAll(faceDistance, facei)
+        {
+            if (absProximity_ < faceDistance[facei])
+            {
+                prune = true;
+            }
+            else
+            {
+                acceptFaces.set(facei);
+            }
+        }
+    }
+
     if (prune)
     {
         labelList pointMap, faceMap;