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diff --git a/thirdparty/thekla_atlas/nvmath/ProximityGrid.h b/thirdparty/thekla_atlas/nvmath/ProximityGrid.h
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+++ b/thirdparty/thekla_atlas/nvmath/ProximityGrid.h
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+#pragma once
+#ifndef NV_MATH_PROXIMITYGRID_H
+#define NV_MATH_PROXIMITYGRID_H
+
+#include "Vector.h"
+#include "ftoi.h"
+
+#include "nvcore/Array.inl"
+
+
+// A simple, dynamic proximity grid based on Jon's code.
+// Instead of storing pointers here I store indices.
+
+namespace nv {
+
+    class Box;
+
+    struct Cell {
+        Array<uint> indexArray;
+    };
+
+    struct ProximityGrid {
+        ProximityGrid();
+
+        void reset();
+        void init(const Array<Vector3> & pointArray);
+        void init(const Box & box, uint count);
+
+        int index_x(float x) const;
+        int index_y(float y) const;
+        int index_z(float z) const;
+        int index(int x, int y, int z) const;
+        int index(const Vector3 & pos) const;
+        
+        uint32 mortonCount() const;
+        int mortonIndex(uint32 code) const;
+
+        void add(const Vector3 & pos, uint key);
+        bool remove(const Vector3 & pos, uint key);
+
+        void gather(const Vector3 & pos, float radius, Array<uint> & indices);
+
+        Array<Cell> cellArray;
+
+        Vector3 corner;
+        Vector3 invCellSize;
+        int sx, sy, sz;
+    };
+
+    // For morton traversal, do:
+    // for (int code = 0; code < mortonCount(); code++) {
+    //   int idx = mortonIndex(code);
+    //   if (idx < 0) continue;
+    // }
+
+
+
+    inline int ProximityGrid::index_x(float x) const {
+        return clamp(ftoi_floor((x - corner.x) * invCellSize.x),  0, sx-1);
+    }
+
+    inline int ProximityGrid::index_y(float y) const {
+        return clamp(ftoi_floor((y - corner.y) * invCellSize.y),  0, sy-1);
+    }
+
+    inline int ProximityGrid::index_z(float z) const {
+        return clamp(ftoi_floor((z - corner.z) * invCellSize.z),  0, sz-1);
+    }
+
+    inline int ProximityGrid::index(int x, int y, int z) const {
+        nvDebugCheck(x >= 0 && x < sx);
+        nvDebugCheck(y >= 0 && y < sy);
+        nvDebugCheck(z >= 0 && z < sz);
+        int idx = (z * sy + y) * sx + x;
+        nvDebugCheck(idx >= 0 && uint(idx) < cellArray.count());
+        return idx;
+    }
+
+    inline int ProximityGrid::index(const Vector3 & pos) const {
+        int x = index_x(pos.x);
+        int y = index_y(pos.y);
+        int z = index_z(pos.z);
+        return index(x, y, z);
+    }
+
+
+    inline void ProximityGrid::add(const Vector3 & pos, uint key) {
+        uint idx = index(pos);
+        cellArray[idx].indexArray.append(key);
+    }
+
+    inline bool ProximityGrid::remove(const Vector3 & pos, uint key) {
+        uint idx = index(pos);
+        return cellArray[idx].indexArray.remove(key);
+    }
+
+} // nv namespace
+
+#endif // NV_MATH_PROXIMITYGRID_H