From 565fa4278eb11a675e80961a3f3e6dca583c8e6e Mon Sep 17 00:00:00 2001
From: osae <osae@iris.no>
Date: Thu, 10 Sep 2015 18:23:00 +0200
Subject: [PATCH] Add some comments and limit to 3 dimensions.

---
 opm/core/grid/GridHelpers.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/opm/core/grid/GridHelpers.cpp b/opm/core/grid/GridHelpers.cpp
index 03528a18..afbaf9b4 100644
--- a/opm/core/grid/GridHelpers.cpp
+++ b/opm/core/grid/GridHelpers.cpp
@@ -59,13 +59,22 @@ const double* beginCellCentroids(const UnstructuredGrid& grid)
 
 double cellCenterDepth(const UnstructuredGrid& grid, int cell_index) 
 {
+    // This method is an alternative to the method cellCentroidCoordinate(...) below.
+    // The cell center depth is computed as a raw average of cell corner depths.
+    // For cornerpoint grids, this is likely to give slightly different depths that seem
+    // to agree with eclipse.
+    assert(grid.dimensions == 3);
+    const int nd = 3; // Assuming 3-dimensional grid ...
+    const int nv = 8; // Assuming 2*4 vertices ...
     double zz = 0.0;
+    // Traverse the bottom and top cell-face
     for (int i=grid.cell_facepos[cell_index+1]-2; i<grid.cell_facepos[cell_index+1]; ++i) {
+        // Traverse the vertices associated with each face
         for (int j=grid.face_nodepos[grid.cell_faces[i]]; j<grid.face_nodepos[grid.cell_faces[i]+1]; ++j) {
-            zz += (grid.node_coordinates+dimensions(grid)*(grid.face_nodes[j]))[2];
+            zz += (grid.node_coordinates+nd*(grid.face_nodes[j]))[nd-1];
         }
     }
-    return zz/8.0;
+    return zz/nv;
 }
 
 double cellCentroidCoordinate(const UnstructuredGrid& grid, int cell_index,