diff --git a/src/Aardvark.Data.Points.Base/Chunk.cs b/src/Aardvark.Data.Points.Base/Chunk.cs
index 6641caa..a7cde68 100644
--- a/src/Aardvark.Data.Points.Base/Chunk.cs
+++ b/src/Aardvark.Data.Points.Base/Chunk.cs
@@ -161,7 +161,7 @@ public static Chunk ImmutableMerge(Chunk a, Chunk b)
                 }
             }
 
-            return new Chunk(ps, cs, ns, js, ks, PartIndexUtils.Union(a.PartIndices, b.PartIndices), new Box3d(a.BoundingBox, b.BoundingBox));
+            return new Chunk(ps, cs, ns, js, ks, PartIndexUtils.MergeIndices(a.PartIndices, a.Count, b.PartIndices, b.Count), new Box3d(a.BoundingBox, b.BoundingBox));
         }
 
         public static Chunk ImmutableMerge(params Chunk[] chunks)
@@ -196,7 +196,7 @@ public static Chunk ImmutableMerge(params Chunk[] chunks)
 
             if (ps == null) throw new Exception("Invariant 4cc7d585-9a46-4ba2-892a-95fce9ed06da.");
             return new Chunk(ps, cs, ns, js, ks,
-                partIndices: PartIndexUtils.Union(chunks.Select(x => x.PartIndices)),
+                partIndices: PartIndexUtils.MergeIndices(chunks.Select(x => (indices: x.PartIndices, count: x.Count))),
                 bbox: new Box3d(chunks.Select(x => x.BoundingBox))
                 );
         }
@@ -378,7 +378,7 @@ public Chunk Union(Chunk other)
                     Append(Normals, other.Normals),
                     Append(Intensities, other.Intensities),
                     Append(Classifications, other.Classifications),
-                    partIndices: PartIndexUtils.Union(PartIndices, other.PartIndices),
+                    partIndices: PartIndexUtils.MergeIndices(PartIndices, Count, other.PartIndices, other.Count),
                     Box.Union(BoundingBox, other.BoundingBox)
                 );
         }
diff --git a/src/Aardvark.Data.Points.Base/PartIndexUtils.cs b/src/Aardvark.Data.Points.Base/PartIndexUtils.cs
index 681c4c9..ea54ff9 100644
--- a/src/Aardvark.Data.Points.Base/PartIndexUtils.cs
+++ b/src/Aardvark.Data.Points.Base/PartIndexUtils.cs
@@ -30,41 +30,169 @@ namespace Aardvark.Data.Points;
 public static class PartIndexUtils
 {
     /// <summary>
-    /// Returns union of two part indices (uint, IList of [byte|short|int]).
+    /// Merges part indices (null, uint, [byte|short|int] array).
     /// </summary>
-    public static object? Union(object? first, object? second)
+    public static object? MergeIndices(object? first, int firstCount, object? second, int secondCount)
+    {
+        // expect: both ranges are defined, or both ranges are null
+        if ((first == null && second != null) || (first != null && second == null)) throw new Exception(
+            "Invariant 874c2220-4779-41f0-9f3e-1c0ef4988da9."
+            );
+
+        checked
+        {
+            return (first, second) switch
+            {
+                (null  , null  ) => null,
+
+                (uint x, uint y) => (x == y) ? x : createArray1(x, firstCount, y, secondCount),
+
+                (uint x, _     ) => second switch
+                {
+                    IReadOnlyList<byte > ys when x <= byte .MaxValue => createArray2((byte )x, firstCount, ys),
+                    IReadOnlyList<short> ys when x <= short.MaxValue => createArray2((short)x, firstCount, ys),
+                    IReadOnlyList<int  > ys when x <= int  .MaxValue => createArray2((int  )x, firstCount, ys),
+                    _ => throw new Exception("Invariant 588fea29-4daa-4356-92a4-369f64ac5778.")
+                },
+
+                (_     , uint y) => second switch
+                {
+                    IReadOnlyList<byte > xs when y <= byte .MaxValue => createArray3(xs, (byte )y, secondCount),
+                    IReadOnlyList<short> xs when y <= short.MaxValue => createArray3(xs, (short)y, secondCount),
+                    IReadOnlyList<int  > xs when y <= int  .MaxValue => createArray3(xs, (int  )y, secondCount),
+                    _ => throw new Exception("Invariant 7ddfc8c0-2e66-45ef-94a9-31d21f6009f9.")
+                },
+
+                (IReadOnlyList<byte > xs, IReadOnlyList<byte > ys) => createArray4(    xs ,     ys ),
+                (IReadOnlyList<byte > xs, IReadOnlyList<short> ys) => createArray4(b2s(xs),     ys ),
+                (IReadOnlyList<byte > xs, IReadOnlyList<int  > ys) => createArray4(b2i(xs),     ys ),
+                (IReadOnlyList<short> xs, IReadOnlyList<byte > ys) => createArray4(    xs , b2s(ys)),
+                (IReadOnlyList<short> xs, IReadOnlyList<short> ys) => createArray4(    xs ,     ys ),
+                (IReadOnlyList<short> xs, IReadOnlyList<int  > ys) => createArray4(s2i(xs),     ys ),
+                (IReadOnlyList<int  > xs, IReadOnlyList<byte > ys) => createArray4(    xs , b2i(ys)),
+                (IReadOnlyList<int  > xs, IReadOnlyList<short> ys) => createArray4(    xs , s2i(ys)),
+                (IReadOnlyList<int  > xs, IReadOnlyList<int  > ys) => createArray4(    xs ,     ys ),
+
+                _ => throw new Exception(
+                    $"Unexpected part indices types {first?.GetType().FullName ?? "null"} and {second?.GetType().FullName ?? "null"}. " +
+                    $"Error 2f0672f5-8c6b-400b-8172-e83a30d70c28"
+                    )
+            };
+
+            object createArray1(uint first, int firstCount, uint second, int secondCount)
+            {
+                var count = firstCount + secondCount;
+                return Math.Max(first, second) switch
+                {
+                    uint max when max <= byte .MaxValue => create((byte )first, (byte )second),
+                    uint max when max <= short.MaxValue => create((short)first, (short)second),
+                    uint max when max <= int  .MaxValue => create((int  )first, (int  )second),
+                    _ => throw new Exception("Invariant 129edb1c-066d-4ff2-8edf-8c5a67191dea.")
+                };
+
+                object create<T>(T x0, T x1) where T : unmanaged
+                {
+                    var xs = new T[count];
+                    for (var i = 0; i < firstCount; i++) xs[i] = x0;
+                    for (var i = firstCount; i < count; i++) xs[i] = x1;
+                    return xs;
+                }
+            }
+
+            object createArray2<T>(T first, int firstCount, IReadOnlyList<T> second) where T : unmanaged
+            {
+                var count = firstCount + second.Count;
+                var xs = new T[count];
+                int j = 0;
+                for (var i = 0; i < firstCount  ; i++) xs[j++] = first;
+                for (var i = 0; i < second.Count; i++) xs[j++] = second[i];
+                return xs;
+            }
+
+            object createArray3<T>(IReadOnlyList<T> first, T second, int secondCount) where T : unmanaged
+            {
+                var count = first.Count + secondCount;
+                var xs = new T[count];
+                int j = 0;
+                for (var i = 0; i < first.Count; i++) xs[j++] = first[i];
+                for (var i = 0; i < secondCount; i++) xs[j++] = second;
+                return xs;
+            }
+
+            object createArray4<T>(IReadOnlyList<T> first, IReadOnlyList<T> second) where T : unmanaged
+            {
+                var count = first.Count + second.Count;
+                var xs = new T[count];
+                int j = 0;
+                for (var i = 0; i < first .Count; i++) xs[j++] = first[i];
+                for (var i = 0; i < second.Count; i++) xs[j++] = second[i];
+                return xs;
+            }
+
+            short[] b2s(IReadOnlyList<byte > xs) { var ys = new short[xs.Count]; for (var i = 0; i < xs.Count; i++) ys[i] = xs[i]; return ys; }
+            int  [] b2i(IReadOnlyList<byte > xs) { var ys = new int  [xs.Count]; for (var i = 0; i < xs.Count; i++) ys[i] = xs[i]; return ys; }
+            int  [] s2i(IReadOnlyList<short> xs) { var ys = new int  [xs.Count]; for (var i = 0; i < xs.Count; i++) ys[i] = xs[i]; return ys; }
+        }
+    }
+
+    /// <summary>
+    /// Merges part indices (null, uint, [byte|short|int] array).
+    /// </summary>
+    public static object? MergeIndices(IEnumerable<(object? indices, int count)> xs)
+    {
+        var (resultIndices, resultCount) = xs.FirstOrDefault();
+        foreach (var (xIndices, xCount) in xs.Skip(1))
+        {
+            MergeIndices(resultIndices, resultCount, xIndices, xCount);
+            resultCount += xCount;
+        }
+        return resultIndices;
+    }
+
+    /// <summary>
+    /// Merges part index ranges (null, (u)int, Range1[bsi]).
+    /// </summary>
+    public static object? MergeRanges(object? first, object? second)
     {
         checked
         {
             return (first, second) switch
             {
                 (null, null) => null,
-                (object x, null) => x,
-                (null, object y) => y,
+                (uint x, null) => x,
+                (int x, null) => x,
+                (Range1b x, null) => x,
+                (Range1s x, null) => x,
+                (Range1i x, null) => x,
+                (null, uint y) => y,
+                (null, int y) => y,
+                (null, Range1b y) => y,
+                (null, Range1s y) => y,
+                (null, Range1i y) => y,
                 (uint x, uint y) => (x == y) ? x : new Range1i(new[] { (int)x, (int)y }),
 
                 (uint x, IList<byte> ys) => ((Range1i)new Range1b(ys)).ExtendedBy((int)x),
                 (uint x, IList<short> ys) => ((Range1i)new Range1s(ys)).ExtendedBy((int)x),
                 (uint x, IList<int> ys) => new Range1i(ys).ExtendedBy((int)x),
 
-                (IList<byte> xs, uint y) => ((Range1i)new Range1b(xs)).ExtendedBy((int)y),
-                (IList<short> xs, uint y) => ((Range1i)new Range1s(xs)).ExtendedBy((int)y),
-                (IList<int> xs, uint y) => new Range1i(xs).ExtendedBy((int)y),
+                //(IList<byte> xs, uint y) => ((Range1i)new Range1b(xs)).ExtendedBy((int)y),
+                //(IList<short> xs, uint y) => ((Range1i)new Range1s(xs)).ExtendedBy((int)y),
+                //(IList<int> xs, uint y) => new Range1i(xs).ExtendedBy((int)y),
 
-                (IList<byte> xs, IList<byte> ys) => (Range1i)new Range1b(xs.Concat(ys)),
-                (IList<byte> xs, IList<short> ys) => (Range1i)new Range1s(xs.Select(x => (short)x).Concat(ys)),
-                (IList<byte> xs, IList<int> ys) => new Range1i(xs.Select(x => (int)x).Concat(ys)),
+                //(IList<byte> xs, IList<byte> ys) => (Range1i)new Range1b(xs.Concat(ys)),
+                //(IList<byte> xs, IList<short> ys) => (Range1i)new Range1s(xs.Select(x => (short)x).Concat(ys)),
+                //(IList<byte> xs, IList<int> ys) => new Range1i(xs.Select(x => (int)x).Concat(ys)),
 
-                (IList<short> xs, IList<byte> ys) => (Range1i)new Range1s(xs.Concat(ys.Select(x => (short)x))),
-                (IList<short> xs, IList<short> ys) => (Range1i)new Range1s(xs.Concat(ys)),
-                (IList<short> xs, IList<int> ys) => new Range1i(xs.Select(x => (int)x).Concat(ys)),
+                //(IList<short> xs, IList<byte> ys) => (Range1i)new Range1s(xs.Concat(ys.Select(x => (short)x))),
+                //(IList<short> xs, IList<short> ys) => (Range1i)new Range1s(xs.Concat(ys)),
+                //(IList<short> xs, IList<int> ys) => new Range1i(xs.Select(x => (int)x).Concat(ys)),
 
-                (IList<int> xs, IList<byte> ys) => new Range1i(xs.Concat(ys.Select(x => (int)x))),
-                (IList<int> xs, IList<short> ys) => new Range1i(xs.Concat(ys.Select(x => (int)x))),
-                (IList<int> xs, IList<int> ys) => new Range1i(xs.Concat(ys)),
+                //(IList<int> xs, IList<byte> ys) => new Range1i(xs.Concat(ys.Select(x => (int)x))),
+                //(IList<int> xs, IList<short> ys) => new Range1i(xs.Concat(ys.Select(x => (int)x))),
+                //(IList<int> xs, IList<int> ys) => new Range1i(xs.Concat(ys)),
 
                 _ => throw new Exception(
-                    $"Unexpected part indices types {first.GetType().FullName} and {second.GetType().FullName}. " +
+                    $"Unexpected part indices types {first?.GetType().FullName ?? "null"} and {second?.GetType().FullName ?? "null"}. " +
                     $"Error 2f0672f5-8c6b-400b-8172-e83a30d70c28"
                     )
             };
@@ -72,38 +200,38 @@ public static class PartIndexUtils
     }
 
     /// <summary>
-    /// Returns union of part indices (uint, IList of [byte|short|int]).
+    /// Merges multiple part index ranges (uint, IList of [byte|short|int]).
     /// </summary>
-    public static object? Union(params object?[] xs)
+    public static object? MergeRanges(params object?[] xs)
     {
         if (xs.Length == 0) return null;
 
         var result = xs[0];
-        for (var i = 1; i < xs.Length; i++) result = Union(result, xs[i]);
+        for (var i = 1; i < xs.Length; i++) result = MergeRanges(result, xs[i]);
         return result;
     }
 
     /// <summary>
-    /// Returns union of part indices (uint, IList of [byte|short|int]).
+    /// Merges multiple part index ranges (uint, IList of [byte|short|int]).
     /// </summary>
-    public static object? Union(IEnumerable<object?> xs)
+    public static object? MergeRanges(IEnumerable<object?> xs)
     {
         var result = xs.FirstOrDefault();
-        foreach (var x in xs.Skip(1)) result = Union(result, x);
+        foreach (var x in xs.Skip(1)) result = MergeRanges(result, x);
         return result;
     }
 
-    public static Range1i ExtendedBy(in Range1i range, object? partIndices)
+    public static Range1i ExtendRangeBy(in Range1i range, object? partIndices)
     {
         checked
         {
             return partIndices switch
             {
-                null => range,
-                uint x => range.ExtendedBy((int)x),
-                IList<byte> xs => range.ExtendedBy((Range1i)new Range1b(xs)),
+                null            => range,
+                uint x          => range.ExtendedBy((int)x),
+                IList<byte> xs  => range.ExtendedBy((Range1i)new Range1b(xs)),
                 IList<short> xs => range.ExtendedBy((Range1i)new Range1s(xs)),
-                IList<int> xs => range.ExtendedBy(new Range1i(xs)),
+                IList<int> xs   => range.ExtendedBy(new Range1i(xs)),
 
                 _ => throw new Exception(
                     $"Unexpected part indices type {partIndices.GetType().FullName}. " +
@@ -149,11 +277,11 @@ public static Range1i ExtendedBy(in Range1i range, object? partIndices)
 
     internal static object? Subset(object? partIndices, IReadOnlyList<int> subsetIndices) => partIndices switch
     {
-        null => null,
-        uint x => x,
-        IList<byte> xs => subsetIndices.MapToArray(i => xs[i]),
+        null            => null,
+        uint x          => x,
+        IList<byte> xs  => subsetIndices.MapToArray(i => xs[i]),
         IList<short> xs => subsetIndices.MapToArray(i => xs[i]),
-        IList<int> xs => subsetIndices.MapToArray(i => xs[i]),
+        IList<int> xs   => subsetIndices.MapToArray(i => xs[i]),
 
         _ => throw new Exception(
             $"Unexpected part indices type {partIndices.GetType().FullName}. " +
diff --git a/src/Aardvark.Geometry.PointSet/Import/ImportChunks.cs b/src/Aardvark.Geometry.PointSet/Import/ImportChunks.cs
index 6a8a6a0..d782689 100644
--- a/src/Aardvark.Geometry.PointSet/Import/ImportChunks.cs
+++ b/src/Aardvark.Geometry.PointSet/Import/ImportChunks.cs
@@ -80,7 +80,7 @@ public static PointSet Chunks(IEnumerable<Chunk> chunks, ImportConfig config)
             {
                 if (chunk.HasPartIndices)
                 {
-                    partIndicesRange = PartIndexUtils.ExtendedBy(partIndicesRange, chunk.PartIndices);
+                    partIndicesRange = PartIndexUtils.ExtendRangeBy(partIndicesRange, chunk.PartIndices);
                 }
 
                 if (config.Verbose)
diff --git a/src/Aardvark.Geometry.PointSet/Octrees/Merge.cs b/src/Aardvark.Geometry.PointSet/Octrees/Merge.cs
index 6033ad9..a426ab9 100644
--- a/src/Aardvark.Geometry.PointSet/Octrees/Merge.cs
+++ b/src/Aardvark.Geometry.PointSet/Octrees/Merge.cs
@@ -549,7 +549,7 @@ static int octant(Cell x)
             {
                 result2 = a.WithSubNodes(subcells!);
                 result2 = InjectPointsIntoTree(
-                    a.PositionsAbsolute, a.Colors?.Value, a.Normals?.Value, a.Intensities?.Value, a.Classifications?.Value,
+                    a.PositionsAbsolute, a.Colors?.Value, a.Normals?.Value, a.Intensities?.Value, a.Classifications?.Value, a.PartIndices,
                     result2, result2.Cell, config);
             }
             else
@@ -802,9 +802,9 @@ private static IPointCloudNode MergeLeafAndLeafWithIdenticalRootCell(IPointCloud
             var ns = Concat(a.Normals?.Value, b.Normals?.Value);
             var js = Concat(a.Intensities?.Value, b.Intensities?.Value);
             var ks = Concat(a.Classifications?.Value, b.Classifications?.Value);
+            var qs = PartIndexUtils.MergeIndices(a.PartIndices, a.PointCountCell, b.PartIndices, b.PointCountCell);
 
-            var chunk = new Chunk(ps, cs, ns, js, ks, partIndices: null /* TODO */, cell.BoundingBox);
-            throw new NotImplementedException("PARTINDICES");
+            var chunk = new Chunk(ps, cs, ns, js, ks, partIndices: qs, cell.BoundingBox);
             if (config.NormalizePointDensityGlobal)
             {
                 chunk = chunk.ImmutableFilterMinDistByCell(cell, config.ParseConfig);
@@ -822,7 +822,7 @@ private static IPointCloudNode MergeLeafAndTreeWithIdenticalRootCell(IPointCloud
             if (a.IsLeaf == false || b.IsLeaf == true) throw new InvalidOperationException();
             if (a.Cell != b.Cell) throw new InvalidOperationException();
 
-            var result = InjectPointsIntoTree(a.PositionsAbsolute, a.Colors?.Value, a.Normals?.Value, a.Intensities?.Value, a.Classifications?.Value, b, a.Cell, config);
+            var result = InjectPointsIntoTree(a.PositionsAbsolute, a.Colors?.Value, a.Normals?.Value, a.Intensities?.Value, a.Classifications?.Value, a.PartIndices, b, a.Cell, config);
             //if (a.PointCountTree + b.PointCountTree != result.PointCountTree) throw new InvalidOperationException("Invariant db336387-4d1a-42fd-a582-48e8cac50fba.");
             if (a.Cell != result.Cell) throw new InvalidOperationException("Invariant 55551919-1a11-4ea9-bb4e-6f1a6b15e3d5.");
             return result;
@@ -899,7 +899,7 @@ ImportConfig config
         }
 
         private static IPointCloudNode InjectPointsIntoTree(
-            IList<V3d> psAbsolute, IList<C4b>? cs, IList<V3f>? ns, IList<int>? js, IList<byte>? ks,
+            IList<V3d> psAbsolute, IList<C4b>? cs, IList<V3f>? ns, IList<int>? js, IList<byte>? ks, object? qs,
             IPointCloudNode a, Cell cell, ImportConfig config
             )
         {
@@ -909,8 +909,7 @@ private static IPointCloudNode InjectPointsIntoTree(
 
             if (a == null)
             {
-                var chunk = new Chunk(psAbsolute, cs, ns, js, ks, partIndices: null /* TODO */, cell.BoundingBox);
-                throw new NotImplementedException("PARTINDICES");
+                var chunk = new Chunk(psAbsolute, cs, ns, js, ks, qs, cell.BoundingBox);
                 if (config.NormalizePointDensityGlobal)
                 {
                     chunk = chunk.ImmutableFilterMinDistByCell(cell, config.ParseConfig);
@@ -955,6 +954,7 @@ private static IPointCloudNode InjectPointsIntoTree(
             var nss = ns != null ? new List<V3f>[8] : null;
             var iss = js != null ? new List<int>[8] : null;
             var kss = ks != null ? new List<byte>[8] : null;
+            var qss = qs != null ? new object?[8] : null;
 
 #if DEBUG
             var bb = cell.BoundingBox;
@@ -988,7 +988,8 @@ private static IPointCloudNode InjectPointsIntoTree(
                 if (pss[j] != null)
                 {
                     if (x == null) throw new InvalidOperationException("Invariant 6afc7ca3-30da-4cb5-9a02-7572085e89bb.");
-                    subcells[j] = InjectPointsIntoTree(pss[j], css?[j], nss?[j], iss?[j], kss?[j], x, cell.GetOctant(j), config);
+                    throw new NotImplementedException("PARTINDICES");
+                    subcells[j] = InjectPointsIntoTree(pss[j], css?[j], nss?[j], iss?[j], kss?[j], qs: null /* TODO */, x, cell.GetOctant(j), config);
                 }
                 else
                 {