ENH: minor consistency improvements for bounding box

- a valid() method (same as !empty() call) for consistency with other
  containers and data types

- a centre() method (same as midpoint() method) for consistency with
  other OpenFOAM geometric entities

src/OpenFOAM/meshes/treeBoundBox/treeBoundBox.C

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011-2016 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2017 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2017-2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -63,10 +63,7 @@ Foam::treeBoundBox::treeBoundBox(const UList<point>& points)
     if (points.empty())
     {
         WarningInFunction
-            << "cannot find bounding box for zero-sized pointField, "
-            << "returning zero" << endl;
-
-        return;
+            << "No bounding box for zero-sized pointField" << nl;
     }
 }
 
@@ -82,10 +79,7 @@ Foam::treeBoundBox::treeBoundBox
     if (points.empty() || indices.empty())
     {
         WarningInFunction
-            << "cannot find bounding box for zero-sized pointField, "
-            << "returning zero" << endl;
-
-        return;
+            << "No bounding box for zero-sized pointField" << nl;
     }
 }
 
@@ -108,7 +102,7 @@ Foam::tmp<Foam::pointField> Foam::treeBoundBox::points() const
 
 Foam::treeBoundBox Foam::treeBoundBox::subBbox(const direction octant) const
 {
-    return subBbox(midpoint(), octant);
+    return subBbox(centre(), octant);
 }
 
 

src/OpenFOAM/meshes/treeBoundBox/treeBoundBox.H

@@ -25,7 +25,7 @@ Class
     Foam::treeBoundBox
 
 Description
-    Standard boundBox + extra functionality for use in octree.
+    Standard boundBox with extra functionality for use in octree.
 
     Numbering of corner points is according to octant numbering.
 
@@ -153,7 +153,7 @@ public:
 
     // Constructors
 
-        //- Construct null setting points to zero
+        //- Construct without any points - an inverted bounding box
         inline treeBoundBox();
 
         //- Construct from a boundBox

src/OpenFOAM/meshes/treeBoundBox/treeBoundBoxI.H

@@ -3,7 +3,7 @@
   \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
    \\    /   O peration     |
     \\  /    A nd           | Copyright (C) 2011 OpenFOAM Foundation
-     \\/     M anipulation  | Copyright (C) 2017 OpenCFD Ltd.
+     \\/     M anipulation  | Copyright (C) 2017-2019 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -80,7 +80,7 @@ inline Foam::point Foam::treeBoundBox::corner(const direction octant) const
 // Returns octant in which point resides. Reverse of subBbox.
 inline Foam::direction Foam::treeBoundBox::subOctant(const point& pt) const
 {
-    return subOctant(midpoint(), pt);
+    return subOctant(centre(), pt);
 }
 
 
@@ -121,7 +121,7 @@ inline Foam::direction Foam::treeBoundBox::subOctant
     bool& onEdge
 ) const
 {
-    return subOctant(midpoint(), pt, onEdge);
+    return subOctant(centre(), pt, onEdge);
 }
 
 
@@ -234,7 +234,7 @@ inline void Foam::treeBoundBox::searchOrder
     FixedList<direction,8>& octantOrder
 ) const
 {
-    vector dist = midpoint() - pt;
+    vector dist = centre() - pt;
 
     direction octant = 0;
 

src/OpenFOAM/meshes/treeBoundBox/treeBoundBoxTemplates.C

@@ -41,10 +41,7 @@ Foam::treeBoundBox::treeBoundBox
     if (points.empty())
     {
         WarningInFunction
-            << "cannot find bounding box for zero-sized pointField, "
-            << "returning zero" << endl;
-
-        return;
+            << "No bounding box for zero-sized pointField" << nl;
     }
 }