diff --git a/src/AcDream.Core/Physics/LandDefs.cs b/src/AcDream.Core/Physics/LandDefs.cs
index a6a61040..8ddbde03 100644
--- a/src/AcDream.Core/Physics/LandDefs.cs
+++ b/src/AcDream.Core/Physics/LandDefs.cs
@@ -141,6 +141,34 @@ public static class LandDefs
         return false;
     }
 
+    /// <summary>
+    /// <c>LandDefs::get_block_offset</c> (pc:69189, @0x0043e630): world-meter offset
+    /// from <paramref name="source"/>'s landblock origin to <paramref name="dest"/>'s.
+    /// ZeroVector when both ids share a landblock (high words equal). The decomp's
+    /// <c>block_byte&lt;&lt;3</c> converts to lcoord (cell) units and the literal
+    /// <c>·24 m/cell</c> then nets to <c>(Δlandblock)·192 m</c> per axis. The
+    /// degenerate <c>arg==0</c> fallbacks are ported verbatim (dest==0 → raw source
+    /// id; source==0 → 0 lcoord). The ONLY cross-cell translation in retail physics:
+    /// a delta of two NAMED cell ids, never an accumulation against a moving center.
+    /// </summary>
+    public static Vector3 GetBlockOffset(uint source, uint dest)
+    {
+        uint srcBlock = source >> 16;
+        uint dstBlock = dest >> 16;
+        if (srcBlock == dstBlock)
+            return Vector3.Zero;
+
+        int srcLx, srcLy;
+        if (source == 0u) { srcLx = 0; srcLy = 0; }
+        else { srcLx = (int)((source >> 21) & 0x7f8u); srcLy = (int)((srcBlock & 0xFFu) << 3); }
+
+        int dstLx, dstLy;
+        if (dest == 0u) { dstLx = (int)source; dstLy = (int)source; }  // retail degenerate guard
+        else { dstLx = (int)((dest >> 21) & 0x7f8u); dstLy = (int)((dstBlock & 0xFFu) << 3); }
+
+        return new Vector3((dstLx - srcLx) * CellLength, (dstLy - srcLy) * CellLength, 0f);
+    }
+
     // Retail cell_in_range: landcell, envcell, or the block sentinel.
     private static bool CellLowInRange(uint low)
         => low is (>= 1u and <= 0x40u) or (>= 0x100u and <= 0xFFFDu) or 0xFFFFu;
diff --git a/src/AcDream.Core/Physics/Position.cs b/src/AcDream.Core/Physics/Position.cs
new file mode 100644
index 00000000..067ffefa
--- /dev/null
+++ b/src/AcDream.Core/Physics/Position.cs
@@ -0,0 +1,23 @@
+using System.Numerics;
+
+namespace AcDream.Core.Physics;
+
+/// <summary>
+/// Retail <c>Frame</c> (acclient.h:30647). <see cref="Origin"/> is LOCAL to the
+/// owning cell: outdoor → X/Y ∈ [0,192) within the landblock, Z = height;
+/// indoor → the EnvCell-relative placement. <see cref="Orientation"/> replaces
+/// retail's <c>m_fl2gv</c> 3×3 local→global matrix (equivalent rotation).
+/// </summary>
+public readonly record struct Frame(Vector3 Origin, Quaternion Orientation);
+
+/// <summary>
+/// Retail <c>Position</c> (acclient.h:30658): the (which-cell, where-inside) pair.
+/// One type for indoor and outdoor. The full 32-bit cell id (high 16 = landblock
+/// prefix, low 16 = cell index) plus the cell-local <see cref="Frame"/>. Neither
+/// half is ever reconstructed from a streaming center — see #145 design spec.
+/// </summary>
+public readonly record struct Position(uint ObjCellId, Frame Frame)
+{
+    public Position(uint objCellId, Vector3 origin, Quaternion orientation)
+        : this(objCellId, new Frame(origin, orientation)) { }
+}
diff --git a/src/AcDream.Core/Physics/ShadowShapeBuilder.cs b/src/AcDream.Core/Physics/ShadowShapeBuilder.cs
index 4fff4106..449b302c 100644
--- a/src/AcDream.Core/Physics/ShadowShapeBuilder.cs
+++ b/src/AcDream.Core/Physics/ShadowShapeBuilder.cs
@@ -4,6 +4,7 @@ using System.Numerics;
 using DatReaderWriter.DBObjs;
 using DatReaderWriter.Enums;
 using DatReaderWriter.Types;
+using DatFrame = DatReaderWriter.Types.Frame;
 
 namespace AcDream.Core.Physics;
 
@@ -88,9 +89,9 @@ public static class ShadowShapeBuilder
             uint gfxId = (uint)setup.Parts[i];
             if (!hasPhysicsBsp(gfxId)) continue;
 
-            Frame partFrame = placementFrame is not null && i < placementFrame.Frames.Count
+            DatFrame partFrame = placementFrame is not null && i < placementFrame.Frames.Count
                 ? placementFrame.Frames[i]
-                : new Frame { Origin = Vector3.Zero, Orientation = Quaternion.Identity };
+                : new DatFrame { Origin = Vector3.Zero, Orientation = Quaternion.Identity };
 
             // BSP radius default; caller substitutes the real BoundingSphere.Radius
             // at registration time when available. Loose-but-safe broadphase value.
diff --git a/tests/AcDream.Core.Tests/Physics/AnimationSequencerTests.cs b/tests/AcDream.Core.Tests/Physics/AnimationSequencerTests.cs
index e911d21d..3508d6fe 100644
--- a/tests/AcDream.Core.Tests/Physics/AnimationSequencerTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/AnimationSequencerTests.cs
@@ -10,6 +10,7 @@ using Xunit;
 // Alias the DatReaderWriter enum so it doesn't clash with
 // AcDream.Core.Physics.MotionCommand (which is a static class of uint constants).
 using DRWMotionCommand = DatReaderWriter.Enums.MotionCommand;
+using DatFrame = DatReaderWriter.Types.Frame;
 
 namespace AcDream.Core.Tests.Physics;
 
@@ -65,7 +66,7 @@ file static class Fixtures
         {
             var pf = new AnimationFrame((uint)numParts);
             for (int p = 0; p < numParts; p++)
-                pf.Frames.Add(new Frame { Origin = origin, Orientation = orientation });
+                pf.Frames.Add(new DatFrame { Origin = origin, Orientation = orientation });
             anim.PartFrames.Add(pf);
         }
         return anim;
@@ -86,8 +87,8 @@ file static class Fixtures
         var pf1 = new AnimationFrame((uint)numParts);
         for (int p = 0; p < numParts; p++)
         {
-            pf0.Frames.Add(new Frame { Origin = fromOrigin, Orientation = fromRot });
-            pf1.Frames.Add(new Frame { Origin = toOrigin,   Orientation = toRot   });
+            pf0.Frames.Add(new DatFrame { Origin = fromOrigin, Orientation = fromRot });
+            pf1.Frames.Add(new DatFrame { Origin = toOrigin,   Orientation = toRot   });
         }
         anim.PartFrames.Add(pf0);
         anim.PartFrames.Add(pf1);
@@ -396,7 +397,7 @@ public sealed class AnimationSequencerTests
         {
             var pf = new AnimationFrame(1);
             float y = 10f - 5f * f;  // 10, 5, 0
-            pf.Frames.Add(new Frame { Origin = new Vector3(0, y, 0), Orientation = Quaternion.Identity });
+            pf.Frames.Add(new DatFrame { Origin = new Vector3(0, y, 0), Orientation = Quaternion.Identity });
             linkAnim.PartFrames.Add(pf);
         }
 
@@ -593,7 +594,7 @@ public sealed class AnimationSequencerTests
         for (int f = 0; f < 4; f++)
         {
             var pf = new AnimationFrame(1);
-            pf.Frames.Add(new Frame { Origin = new Vector3(0, 0, f), Orientation = Quaternion.Identity });
+            pf.Frames.Add(new DatFrame { Origin = new Vector3(0, 0, f), Orientation = Quaternion.Identity });
             anim.PartFrames.Add(pf);
         }
 
@@ -1006,7 +1007,7 @@ public sealed class AnimationSequencerTests
         anim.Flags = AnimationFlags.PosFrames;
         for (int f = 0; f < 4; f++)
         {
-            anim.PosFrames.Add(new Frame
+            anim.PosFrames.Add(new DatFrame
             {
                 Origin      = new Vector3(1f, 0f, 0f),
                 Orientation = Quaternion.Identity,
@@ -1153,7 +1154,7 @@ public sealed class AnimationSequencerTests
         for (int f = 0; f < 10; f++)
         {
             var pf = new AnimationFrame(1);
-            pf.Frames.Add(new Frame { Origin = new Vector3(0, 0, f), Orientation = Quaternion.Identity });
+            pf.Frames.Add(new DatFrame { Origin = new Vector3(0, 0, f), Orientation = Quaternion.Identity });
             anim.PartFrames.Add(pf);
         }
 
@@ -1204,7 +1205,7 @@ public sealed class AnimationSequencerTests
         for (int f = 0; f < 10; f++)
         {
             var pf = new AnimationFrame(1);
-            pf.Frames.Add(new Frame { Origin = new Vector3(0, 0, f), Orientation = Quaternion.Identity });
+            pf.Frames.Add(new DatFrame { Origin = new Vector3(0, 0, f), Orientation = Quaternion.Identity });
             anim.PartFrames.Add(pf);
         }
 
diff --git a/tests/AcDream.Core.Tests/Physics/LandDefsBlockOffsetTests.cs b/tests/AcDream.Core.Tests/Physics/LandDefsBlockOffsetTests.cs
new file mode 100644
index 00000000..a9a75b35
--- /dev/null
+++ b/tests/AcDream.Core.Tests/Physics/LandDefsBlockOffsetTests.cs
@@ -0,0 +1,41 @@
+using System.Numerics;
+using AcDream.Core.Physics;
+using Xunit;
+
+namespace AcDream.Core.Tests.Physics;
+
+public class LandDefsBlockOffsetTests
+{
+    // get_block_offset(src, dst) returns the world-meter offset from src's
+    // landblock origin to dst's landblock origin. block_byte<<3 = lcoord, *24 m/cell
+    // → nets to (Δlandblock)·192 m. Same landblock → Zero. Decomp @0x0043e630.
+
+    [Fact]
+    public void SameLandblock_ReturnsZero()
+    {
+        // both 0xC95B
+        Assert.Equal(Vector3.Zero, LandDefs.GetBlockOffset(0xC95B0001u, 0xC95B0008u));
+    }
+
+    [Fact]
+    public void SouthNeighbour_IsMinus192Y()
+    {
+        // 0xC95B (lbY=0x5B) → 0xC95A (lbY=0x5A): one landblock south = (0,-192,0).
+        // This is the exact #145 case: correct origin for 0xC95A relative to 0xC95B.
+        Assert.Equal(new Vector3(0f, -192f, 0f), LandDefs.GetBlockOffset(0xC95B0001u, 0xC95A0001u));
+    }
+
+    [Fact]
+    public void EastNeighbour_IsPlus192X()
+    {
+        // 0xC95B (lbX=0xC9) → 0xCA5B (lbX=0xCA): one landblock east = (+192,0,0).
+        Assert.Equal(new Vector3(192f, 0f, 0f), LandDefs.GetBlockOffset(0xC95B0001u, 0xCA5B0001u));
+    }
+
+    [Fact]
+    public void DiagonalNeighbour_CombinesBothAxes()
+    {
+        // 0xC95B → 0xCA5C: lbX +1 (+192), lbY +1 (+192).
+        Assert.Equal(new Vector3(192f, 192f, 0f), LandDefs.GetBlockOffset(0xC95B0001u, 0xCA5C0001u));
+    }
+}
diff --git a/tests/AcDream.Core.Tests/Physics/ShadowShapeBuilderTests.cs b/tests/AcDream.Core.Tests/Physics/ShadowShapeBuilderTests.cs
index b1679358..2d94753a 100644
--- a/tests/AcDream.Core.Tests/Physics/ShadowShapeBuilderTests.cs
+++ b/tests/AcDream.Core.Tests/Physics/ShadowShapeBuilderTests.cs
@@ -6,6 +6,7 @@ using DatReaderWriter.DBObjs;
 using DatReaderWriter.Enums;
 using DatReaderWriter.Types;
 using Xunit;
+using DatFrame = DatReaderWriter.Types.Frame;
 
 namespace AcDream.Core.Tests.Physics;
 
@@ -37,9 +38,9 @@ public class ShadowShapeBuilderTests
                 {
                     Frames =
                     {
-                        new Frame { Origin = Vector3.Zero, Orientation = Quaternion.Identity },
-                        new Frame { Origin = Vector3.Zero, Orientation = Quaternion.Identity },
-                        new Frame { Origin = Vector3.Zero, Orientation = Quaternion.Identity }
+                        new DatFrame { Origin = Vector3.Zero, Orientation = Quaternion.Identity },
+                        new DatFrame { Origin = Vector3.Zero, Orientation = Quaternion.Identity },
+                        new DatFrame { Origin = Vector3.Zero, Orientation = Quaternion.Identity }
                     }
                 }
             }
diff --git a/tests/AcDream.Core.Tests/Rendering/Vfx/EntityScriptActivatorTests.cs b/tests/AcDream.Core.Tests/Rendering/Vfx/EntityScriptActivatorTests.cs
index 4a5bd3fe..4f832dab 100644
--- a/tests/AcDream.Core.Tests/Rendering/Vfx/EntityScriptActivatorTests.cs
+++ b/tests/AcDream.Core.Tests/Rendering/Vfx/EntityScriptActivatorTests.cs
@@ -7,6 +7,7 @@ using AcDream.Core.World;
 using DatReaderWriter.Types;
 using Xunit;
 using DatPhysicsScript = DatReaderWriter.DBObjs.PhysicsScript;
+using DatFrame = DatReaderWriter.Types.Frame;
 
 namespace AcDream.Core.Tests.Rendering.Vfx;
 
@@ -140,7 +141,7 @@ public sealed class EntityScriptActivatorTests
         var hookSink = new ParticleHookSink(system);
 
         // Hook offset = (1, 0, 0) in entity-local frame.
-        var hookOffset = new Frame
+        var hookOffset = new DatFrame
         {
             Origin = new Vector3(1f, 0f, 0f),
             Orientation = Quaternion.Identity,
@@ -194,7 +195,7 @@ public sealed class EntityScriptActivatorTests
         var system  = new ParticleSystem(registry);
         var hookSink = new ParticleHookSink(system);
 
-        var script = BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100u, Offset = new Frame() }));
+        var script = BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100u, Offset = new DatFrame() }));
         var table  = new Dictionary<uint, DatPhysicsScript> { [0xAAu] = script };
         var runner = new PhysicsScriptRunner(
             id => table.TryGetValue(id, out var s) ? s : null,
@@ -257,7 +258,7 @@ public sealed class EntityScriptActivatorTests
         var system = new ParticleSystem(registry);
         var hookSink = new ParticleHookSink(system);
 
-        var hookOffset = new Frame { Origin = new Vector3(1f, 0, 0), Orientation = Quaternion.Identity };
+        var hookOffset = new DatFrame { Origin = new Vector3(1f, 0, 0), Orientation = Quaternion.Identity };
         var script = BuildScript(
             (0.0, new CreateParticleHook { EmitterInfoId = 100u, Offset = hookOffset, PartIndex = 1 }));
         var table = new Dictionary<uint, DatPhysicsScript> { [0xAAu] = script };
@@ -297,7 +298,7 @@ public sealed class EntityScriptActivatorTests
         var system = new ParticleSystem(registry);
         var hookSink = new ParticleHookSink(system);
 
-        var script = BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100u, Offset = new Frame() }));
+        var script = BuildScript((0.0, new CreateParticleHook { EmitterInfoId = 100u, Offset = new DatFrame() }));
         var table = new Dictionary<uint, DatPhysicsScript> { [0xAAu] = script };
         var runner = new PhysicsScriptRunner(
             id => table.TryGetValue(id, out var s) ? s : null,
diff --git a/tests/AcDream.Core.Tests/Streaming/GpuWorldStateActivatorTests.cs b/tests/AcDream.Core.Tests/Streaming/GpuWorldStateActivatorTests.cs
index e5a2034e..c04a5718 100644
--- a/tests/AcDream.Core.Tests/Streaming/GpuWorldStateActivatorTests.cs
+++ b/tests/AcDream.Core.Tests/Streaming/GpuWorldStateActivatorTests.cs
@@ -10,6 +10,7 @@ using DatReaderWriter.DBObjs;
 using DatReaderWriter.Types;
 using Xunit;
 using DatPhysicsScript = DatReaderWriter.DBObjs.PhysicsScript;
+using DatFrame = DatReaderWriter.Types.Frame;
 
 namespace AcDream.Core.Tests.Streaming;
 
@@ -43,7 +44,7 @@ public sealed class GpuWorldStateActivatorTests
         script.ScriptData.Add(new PhysicsScriptData
         {
             StartTime = 0.0,
-            Hook = new CreateParticleHook { EmitterInfoId = 100u, Offset = new Frame() },
+            Hook = new CreateParticleHook { EmitterInfoId = 100u, Offset = new DatFrame() },
         });
         var table = new Dictionary<uint, DatPhysicsScript> { [scriptId] = script };