Syplheed-Reborn/docs/re/structures/mcol-collision.md

# `MCOL` — the same container as `REGN`, and the same map parameters

**🟡 Opened 2026-08-26.** `MCOL` sits beside `REGN` in `hidden/MiscBin.pak`, 11
of each, and has never been decoded. This page establishes what it shares with
`REGN` — which is a lot, and gives the next attempt a large head start.

## ✅ Same container

Over all **11** objects:

| | |
|---|---|
| `POF0` fixup table at `data_size@+4` + 16 | **11 / 11** |
| bbox pad words are `1.0` / `1.0` / `0.0` at `+0x1C`, `+0x2C`, `+0x3C` | **11 / 11** |
| `extent == max − min` for the `0x30` block | **11 / 11** |

So the header prefix is byte-for-byte the same shape as `REGN`'s: magic, data
size, then bbox min / bbox max / extent as `f32[4]`, then a triple at `0x40`.
The `POF0` mechanism applies, which means **the `chunk + 0x10` base and the
loader's own pointer list are available here too** — the two things that cracked
`REGN`.

## ✅ And the same map parameters, exactly

The bounding boxes and the `0x40` triple are not merely similar — the
distributions are **identical**:

| | `MCOL` | `REGN` |
|---|---|---|
| bbox ±250 000 | 2 | 2 |
| bbox ±50 000 | 6 | 6 |
| bbox ±25 000 | 3 | 3 |
| `0x40` = 50 000 | 2 | 2 |
| `0x40` = 10 000 | 9 | 9 |

Eleven maps, and for each one an `MCOL` and a `REGN` describing the same volume
at the same cell size. `0x40` is the **cell size** in `REGN`; the same values in
the same multiplicities here is strong evidence it is the cell size in `MCOL`
too — though note this is a match of *distributions*, not a demonstrated
object-to-object pairing, which would need the two linked by name or by a stage's
tables.

## ❔ What is not yet known

* **Everything past `0x40`.** `MCOL`'s words at `0x50`–`0x84` do **not** look
  like `REGN`'s (`REGN` has grid dims at `0x50`, six `u16` counts at `0x60` and
  six section pointers at `0x70`; `MCOL` has a large value, two mid-range values
  and `112` at `0x50`, mostly zeros at `0x60`, and `0x05050501` at `0x70`). The
  headers agree on the spatial prefix and diverge after it.
* **Everything past `0x40`** — but see below; the pointer layout is now known.


## ✅ The pointer layout, from `POF0`

**2026-08-26.** Running the known-good decoder (`regn_decode.py` on
`auto/regn-reader`) rather than my own broken one. Sanity check first: on `REGN`
it returns header slots `0x70`–`0x84` exactly — the six section pointers — so the
tool and my use of it are right.

On `MCOL`, over all **11** objects:

| | |
|---|---|
| header-region relocated slots are **exactly `0x54`, `0x58`, `0x5C`, `0x74`** | **11 / 11** |
| slot `0x5C` resolves to **`0x80`** — the first byte after the header | **11 / 11** |
| slot `0x74` resolves to **(first array pointer − 8)** | **10 / 11** |

So `MCOL` has **four** top-level pointers where `REGN` has six, and one of them
(`0x5C`) always addresses the data immediately following the header.

**The bulk of the relocations form record arrays.** 92.7 % of the gaps between
consecutive relocated words are **32 bytes**, arranged in 7–127 contiguous runs
per object. Combined with `0x74` landing 8 bytes before the first of them, the
reading is an array of **32-byte records each carrying one pointer at `+8`**.

What the four targets look like:

    0x5C -> 0x80     c685620b 4596789d 4694b3b5 44a9a634   floats
    0x54 -> …        c6826964 456b1aa4 469ab065 c685cfe8   floats
    0x58 -> …        00000001 00020003 00040005 00050004   small ints / u16 pairs
    0x74 -> …        00000001 00000001 00007710 00000000   counts, then the array

Two float blocks, an index block and a record array is the shape of a mesh —
which is what a name like `MCOL` beside a navigation mesh would suggest. 🟡 That
is a reading of the shape; none of the four blocks has been decoded.

❔ Still open: the record layout, what the index block indexes, the **one object
in eleven** where `0x74` does not land 8 before the array, and the 7.3 % of gaps
that are not 32 (they are the boundaries between runs, but that has not been
checked).

## 🟡 The 32-byte record — a cell entry, and there are two interleaved arrays

**2026-08-26.** Reading each record as 8 big-endian words (record start =
pointer slot − 8), the first entries of the smallest object are:

    @0x6780  00000001 00000001 00007710 00000000 00000000 00000000 00000000 47295092
    @0x67A0  01000001 00000001 00007730 00000000 …
    @0x67C0  02000001 00000001 00007750 00000000 46023555 C6023555 C6023555 471FA1A7
    @0x6820  00010001 00000001 000077B0 00000000 …

Word 0 read as **four bytes** is `(x, y, z, 1)` — a **3-D cell index**. That
object's grid is 5×5×5 (bbox ±25 000, cell 10 000), and the values run 0–4 in
the first byte and step the second byte at the right point. Words 4–6 are a
position and word 7 a positive scalar — a bounding sphere. Word 1 is a count and
word 2 the relocated pointer.

**Every record pointer lands in the same region — 8 976 / 8 976 (100 %)** — and
each points 0xFA0 further on with the same stride, so there are **two parallel
arrays**, not one: array A at `0x6780` and array B at `0x7720`.

### The 50 % is the tell, not a failure

Testing the cell-index reading over *all* relocated records gives almost exactly
half:

    byte 3 == 1                                  4 491 / 8 976  (50.03 %)
    bytes 0..2 a valid cell index                4 488          (50.00 %)
    the record's sphere reaches that cell        4 485          (49.97 %)

Three independent criteria all landing on 50.0 % is not a partial fit — it says
**half the records are not this type**. The `POF0` slot list interleaves both
arrays, and I was testing array B's records against array A's layout. Reported as
a rate it would read like a half-working hypothesis; split by array it is two
clean populations.

🟡 So array A is a **per-cell record** — cell index, count, pointer into array B,
bounding sphere — the same role `REGN`'s section 3 plays. ❔ Array B's layout is
unread, and the split has not yet been re-run per array to confirm 100 % on A.

### ✅ Split by array, and it goes to 100 %

Done. Separating the records by address and re-running the same three criteria:

| | array A (2 509) | array B (6 467) |
|---|---|---|
| byte 3 of word 0 == 1 | **100.00 %** | 30.65 % |
| bytes 0–2 a valid cell index | **100.00 %** | 30.60 % |
| the record's sphere reaches that cell | **99.92 %** | — |

**Array A is the per-cell record**, exactly as read: cell index `(x, y, z)`, a
count, a pointer into array B, and a bounding sphere — the same role `REGN`'s
section 3 plays. Array B is a different record type; its ~30 % is incidental,
and it is the control that shows A's 100 % is not something any 32-byte block
would score.

Worth noting the split was crude — "first half by address", giving 2 509 vs
6 467 rather than an even cut — and A still came out clean at 100 %. A rough
partition that isolates a perfect population is stronger evidence than a careful
one that isolates a good-ish population.

### ✅ A → B is one-to-one, and every count is 1

Filtering array A by the cell-index criteria (so only genuine A records) and
following each one's pointer, over all **11** objects:

| | |
|---|---|
| every A record points at a **distinct** B record | **11 / 11** |
| every A record's count field is **exactly 1** | **11 / 11** |

Per object the A-record count is the number of **occupied cells** — 110, 118,
117, 488, 488, 575, 514, 468, 492, 546, 572 — and the total of the count fields
equals it exactly.

That is the *same* design `REGN` uses: this corpus already records for `REGN`
that "every occupied cell has count exactly 1 — total items equals occupied
cells". Two sibling formats, same cell-index convention. It is a further
independent confirmation of the A-record reading, since the filter and the
cardinality are unrelated criteria.

### ❌ Array B resisted a first pass, and the tests I reached for were bad ones

I could not read B's record layout this iteration, and both attempts failed in
ways worth recording rather than retrying:

* **The boundary was off by 8 again.** Dumping from `pointer − 8` (as A's layout
  needed) produced records that begin with what is plainly the *tail* of the
  previous structure — a zero and `0x47295092`, the same radius value A's first
  record carries. Same mistake as the `0x74` check two iterations ago.
* **The `u16`-index test had no power.** The `0x5C` block holds ~1 232 points, so
  "is this `u16` below the point count" is satisfied by almost any small value —
  and duly reported 100 % at seven different offsets. That is the *fourth* time
  in this pair of formats that a bound-check against a large collection has
  produced a meaningless 100 %.

❔ So B's layout is open. **What would have power**: B records are 1:1 with
occupied cells and A already carries the cell's bounding sphere, so a candidate
field in B can be tested by whether it is spatially consistent with *that
specific cell* — the same design that worked for `REGN`'s faces, and the same
design that these two bound-checks lack.

## ✅ Array B decoded — `{count, u16 index array}`, and the chain closes

**2026-08-26.** Two corrections got there.

**Where the other relocations live.** `MCOL` has 9 020 relocated words and only
4 488 are A-record pointers. I assumed the rest sat at `B+8`, mirroring A —
**refuted, 0 / 4 488**. Measuring their offset from the nearest preceding B
record instead:

    at B + 4              4 488  (99.0 %)
    before the first B       44  (1.0 %)

and those 44 are exactly the four header pointers × 11 objects. **Nothing
unaccounted for.**

**So B is `{u32 count, pointer}`** — pointer at `+4`, not `+8`. Read that way:

    B@0x7720   count 0x2B   ptr 0x84D0
    B@0x7740   count 0x1C   ptr 0x8526      0x8526 − 0x84D0 = 0x56 = 2 × 0x2B
    B@0x7760   count 0x02   ptr 0x855E      0x855E − 0x8526 = 0x38 = 2 × 0x1C
    B@0x7780   count 0x02   ptr 0x8562      = 2 × 2

The pointers advance by exactly twice the count — a **packed `u16` array**, no
padding. Over all 11 objects:

| | |
|---|---|
| consecutive B pointers differ by **exactly `2 × count`** | **4 477 / 4 477 (100.00 %)** |
| the `u16` entries are valid `0x5C` point indices | 18 379 / 18 379 |

The first row is the load-bearing one: an exact arithmetic identity over 4 477
consecutive pairs. (The second is the same weak bound-check flagged above — the
point block is large, so almost any `u16` passes. It is consistent, not
evidence.)

### The chain

    position → cell → A record {cell index, count 1, →B, bounding sphere}
                    → B record {count n, →u16[n]}
                    → n indices into the 0x5C point block   ← wrong, see below

which is the same shape as `REGN`'s `cell → item → refs → geometry`, as the two
formats' shared header and shared count-1 convention already suggested.

❔ Still open: the `0x54` and `0x58` blocks (neither is reached by this chain).
What the `u16` entries index is **not** the point block — see immediately below.

## ❌ The `u16` entries do NOT index the point block — and the weak test said they did

**2026-08-26.** Two tests, and the contrast between them is the point of this
section.

**Not a triangle list.** If the `u16` array held triangle corners, every count
would be divisible by 3. Counts modulo 3 across all objects:

    n % 3 == 0   639        n % 3 == 1   2 063        n % 3 == 2   1 786

Spread across all three residues. Refuted.

**Not cell-local either.** A B record is reached *through* a specific cell, so a
point it references should lie in that cell. With a random-point control:

| | |
|---|---|
| referenced point inside the cell that reached it | 142 / 17 871 = **0.79 %** |
| a random point inside that cell (control) | 85 / 17 871 = **0.48 %** |

Chance. So whatever the `u16`s address, it is not the `0x5C` point block in any
spatially meaningful way.

### ⚠️ This is the bound-check hazard caught in the act

One section above, the same `u16` entries scored **18 379 / 18 379 (100 %)** on
"are these valid `0x5C` point indices". I flagged that at the time as the weak
bound-check rather than evidence, and recorded it as *consistent* rather than as
a finding. **That caution was correct**: the powered version of the same question
now returns chance.

This is the fifth appearance of the pattern across `REGN` and `MCOL`, and the
first time both halves have been run side by side on the same field, so it is
worth stating exactly:

> A bound-check asks *"could this be an index?"*. Almost always, yes — the answer
> is set by how large the target collection is, not by whether the field means
> anything. The powered version asks *"does the thing it points at make sense
> where it was reached from?"*, and only that version can be wrong.

Had the 100 % been written up as the decode, this page would now carry a
confident and false statement about `MCOL`'s geometry.

❔ What the `u16`s index is open. A datum for the next attempt: the maximum
`u16` is consistently ≈ **0.75 ×** the point count (923/1 232, 1 019/1 360,
1 163/1 552, 59/80) — too consistent to be coincidence, and not explained.

> **Resolved in the next section.** 0.75 is `12 / 16`: "the point count" was
> computed with an assumed 12-byte stride that the block lengths refute. The
> `u16`s *do* index this block — at stride 16. Both this test and the 100 %
> bound-check above were reading the block wrongly; only the powered one could
> say so.
## ✅ The `0x5C` block is **bounding spheres at stride 16** — and that explains the 0.75

**2026-08-26.** The unexplained ≈0.75 ratio left at the end of the section above
was **12 / 16**: my own stride. I had been reading the `0x5C` block as 12-byte
points because `REGN`'s vertex section is 12 bytes, and never checked the
assumption.

It does not survive the cheapest possible check — **`len(0x5C)` is not a
multiple of 12** in 5 of the 11 objects, so a 12-byte stride was never
arithmetically possible:

| object | `len(0x5C)` | ÷12 | ÷16 | max `u16` |
|---|---|---|---|---|
| `2cf7eb47` | 960 | 80.00 | 60 | 59 |
| `cbb99d34` | 192 | 16.00 | 12 | 11 |
| `d84a95fb` | 3 488 | 290.67 ❌ | 218 | 217 |
| `db066592` | 12 640 | 1 053.33 ❌ | 790 | 789 |
| `db61c506` | 2 144 | 178.67 ❌ | 134 | 133 |
| `dc44fe0c` | 2 784 | 232.00 | 174 | 173 |
| `dc4b0896` | 14 784 | 1 232.00 | 924 | 923 |
| `dd89a110` | 18 624 | 1 552.00 | 1 164 | 1 163 |
| `df4628c2` | 4 160 | 346.67 ❌ | 260 | 259 |
| `e084c13c` | 192 | 16.00 | 12 | 11 |
| `e16460cf` | 16 320 | 1 360.00 | 1 020 | 1 019 |

At stride 16 the relation is not "≈0.75×" but **exact, in 11 / 11 objects**:

    max u16  ==  len(0x5C) / 16  −  1

The `u16` array indexes the `0x5C` block at stride 16, and *covers it fully* —
the largest index is always the last element.

### The record is `{ centre f32[3], radius f32 }`

Read at stride 16, the first three floats lie inside the object's own bounding
box in **every record of every object**, and are never unit-length, so this is a
position and not a plane normal. The fourth float is a positive scalar which is
**not** `|centre|`.

The powered test is the one the previous section said was needed: a `u16` is
reached *through a specific cell*, so the thing it names should be present in
that cell. Treating the record as a sphere and the cell as its grid box:

| | |
|---|---|
| **referenced sphere intersects the cell that reached it** | **18 559 / 18 577 = 99.90 %** |
| a random sphere from the same object (control) | 2 233 / 18 577 = 12.02 % |

And both halves of the record are load-bearing — ablating either one costs most
of the signal:

| | |
|---|---|
| centre + radius | **99.90 %** |
| centre alone, radius treated as 0 | 26.75 % |
| centre kept, radius shuffled within the object | 70.19 % |
| radius kept, centre shuffled within the object | 23.74 % |

So the `0x5C` block is a **broad-phase bounding-sphere array**, and each grid
cell's `u16` list names the primitives that reach into that cell — the standard
shape for a collision mesh, and the sibling of `REGN`'s `cell → tetrahedra`.

### The list is a *subset* of what the spheres allow, which is the expected direction

Testing the converse — is the `u16` set **exactly** the set of spheres that
intersect the cell? — gives **17 / 4 488 cells (0.38 %)**, with 46 525 spheres
intersecting a cell but absent from its list. That is the right direction and
not a problem: a bounding sphere is a conservative bound on the primitive inside
it, so "sphere overlaps cell" must be implied by membership but cannot imply it.
The tighter true geometry lives in the `0x54` / `0x58` blocks, still undecoded.

❔ **18 exceptions (0.10 %)** go the wrong way — listed, but the sphere misses
the cell, by `dist / radius` of 1.004 to 1.129. They are spread over 7 of the 11
objects with no object dominating, so this looks like a small build-time margin
rather than a decode error, but it is **not explained** and is recorded as open.

### The chain, corrected

    position → cell → A record {cell index (x,y,z,1), count 1, →B at +8, bounding sphere}
                    → B record {u32 count, →u16[n] at +4}
                    → n indices into the 0x5C array of 16-byte bounding spheres

❔ Still open: the `0x54` and `0x58` blocks — the actual collision geometry that
these spheres bound. Their lengths are **not** a constant multiple of the sphere
count (`0x58 / n` is ≈6.0 for the large objects but 6.13 and 6.67 for the two
smallest), so at least one of them is variable-stride or has its own count.

## ✅✅ `MCOL` is a **closed triangle collision mesh** — decoded

**2026-08-26.** The header's `0x50` word, which the first section on this page
dismissed as "a large value", is **two `u16` counts**, and they give both
remaining blocks a stride:

    0x50  u16 vertex count     0x52  u16 triangle count

Every derived length is exact in **11 / 11** objects:

| | |
|---|---|
| `len(0x54) == align16(12 × vertices)` | **11 / 11** |
| `len(0x58) == align16(6 × triangles)` | **11 / 11** |
| triangle count `==` sphere count (`len(0x5C)/16`) | **11 / 11** |

| object | verts | tris | `0x54` | `0x58` | spheres |
|---|---|---|---|---|---|
| `2cf7eb47` | 34 | 60 | 416 | 368 | 60 |
| `cbb99d34` | 8 | 12 | 96 | 80 | 12 |
| `d84a95fb` | 111 | 218 | 1 344 | 1 312 | 218 |
| `db066592` | 405 | 790 | 4 864 | 4 752 | 790 |
| `db61c506` | 73 | 134 | 880 | 816 | 134 |
| `dc44fe0c` | 89 | 174 | 1 072 | 1 056 | 174 |
| `dc4b0896` | 502 | 924 | 6 032 | 5 552 | 924 |
| `dd89a110` | 632 | 1 164 | 7 584 | 6 992 | 1 164 |
| `df4628c2` | 134 | 260 | 1 616 | 1 568 | 260 |
| `e084c13c` | 8 | 12 | 96 | 80 | 12 |
| `e16460cf` | 554 | 1 020 | 6 656 | 6 128 | 1 020 |

The two smallest objects are the tell on their own: **8 vertices and 12
triangles**, and their `0x54` block is exactly the eight `±250 000` corners of
the map's bounding box. That is a cube as a triangle mesh — a map whose only
collision is its outer wall.

### Sphere *i* bounds triangle *i*, and it is tight

The algebraic test, which cannot pass by accident:

| | |
|---|---|
| all three vertices of triangle *i* inside sphere *i* | **4 768 / 4 768 = 100.00 %** |
| …and the sphere is **tight** (`max‖v−c‖ / r` within 1 %) | **4 768 / 4 768 = 100.00 %** |
| sphere *i* encloses a *random* triangle (control) | 63 / 4 768 = **1.32 %** |

`max‖v−c‖ / r` has median **0.99990** across every triangle of every object, so
the radius is the enclosing radius times a fixed **1.0001** epsilon. That is the
same 1.0001 visible by hand on the cube, where the sphere of a box-face triangle
came out as `250 000·√2 × 1.0001`.

### And the mesh is closed

| | |
|---|---|
| edges shared by exactly two triangles | **7 152 / 7 152 = 100.00 %** |
| degenerate triangles | **0** |
| vertices never referenced by a triangle | **0** |

A watertight manifold with no orphans — which is what a collision hull must be,
and a result that a wrong stride or a wrong index width could not produce.
`cbb99d34` has Euler characteristic `V − E + F = 8 − 18 + 12 = 2` (one closed
surface, the box); `2cf7eb47` has 4, i.e. two closed components.

### The cell lists are a correct broad phase

Re-running the completeness test with the *actual triangles* instead of their
bounding spheres, using a separating-axis triangle/box test:

| | |
|---|---|
| cells whose `u16` list is exactly the overlapping triangle set | 3 973 / 4 488 = **88.52 %** |
| triangles overlapping a cell but **absent** from its list | **3** |
| triangles listed but not overlapping | 730 (3.9 % of 18 577 entries) |

Three misses in 18 577 entries: the lists are **complete**, which is the property
a broad phase must have — a collision query that walks one cell's list cannot
miss a triangle it should have hit. The 730 extras are conservative and harmless.

Their size identifies the builder's own test as sitting **between** an exact
triangle/box test and a cheap AABB one: replacing the SAT test with "triangle
AABB overlaps cell" gives **0** listed-but-not-overlapping (so every listed
triangle's AABB does reach its cell) but 7 913 missing, so the builder is
stricter than AABB and looser than exact — an exact test with a margin. This
also explains the **18 sphere misses** left open in the section above: they were
never sphere-vs-cell facts, they are that same margin.

### The full format

    0x00  magic 'MCOL'
    0x04  data size (POF0 table at data_size + 16)
    0x10  bbox min f32[4]      0x20  bbox max f32[4]      0x30  extent f32[4]
    0x40  cell size f32[3]
    0x50  u16 vertex count     0x52  u16 triangle count
    0x54  → vertex array       f32[3] × nv,  padded to 16
    0x58  → triangle array     u16[3] × nt,  padded to 16
    0x5C  → bounding spheres   {centre f32[3], radius f32} × nt   (= 0x80)
    0x74  → grid cell array    32-byte A records, pointer at +8

    position → cell → A {cell index (x,y,z,1), count 1, →B, bounding sphere}
                    → B {u32 count, →u16[n] at +4}
                    → n triangle indices

Reproduce with `tools/re-capture/mcol_probe.py verify` (recorded in
[`../data/mcol-verify.txt`](../data/mcol-verify.txt)); `mcol_probe.py obj` writes
any object out as a Wavefront OBJ.

❔ Still open: `MCOL` objects are **not name-resolved**, so which map each one
belongs to — and the object-to-object pairing with `REGN` that the header
distributions only hint at — is still unknown. And the runtime consumer has not
been found, the same gap `REGN` has.

## ✅✅ All 40 `MiscBin` entries are name-resolved, and the `REGN`↔`MCOL` pairing is now demonstrated

**2026-08-26.** The names are not in `MiscBin`. They are the values of three
fields of the per-stage `StageResource` object (IDXD schema `3c9ae32e`, present
in every `dat/GP_MAIN_GAME_<lang>.pak`), and each hashes with the ordinary pak
`name_hash` straight to a TOC entry:

    Phase_1   MapPath = 'S14_p1_AsteroidVolume_wp.rgn'   → REGN
              MapMesh = 'S14_p1_AsteroidVolume_wp.col'   → MCOL
              CollisionMeshes = 'CollisionSet_S14.bin'

**40 / 40 entries resolved, with no hash collisions** — the 11 `REGN`, the 11
`MCOL`, and the 18 remaining 1 675 148-byte entries, which are the
`CollisionSet_S01…S16.bin`, `CollisionSet_Tutorial.bin` and
`CollisionSet_test.bin` blobs. Nothing in the archive is unaccounted for.

The route in was the `.pe`: `MapMesh` and `MapPath` sit adjacent in the string
table at file offset 651 540, next to `CollisionMeshes` and `3DSetup.tbl`.

### The pairing, upgraded from "matching distributions" to an object-level link

The first section of this page could only say that `MCOL` and `REGN` had the
*same distribution* of bounding boxes and cell sizes, and flagged that this was
not a demonstrated object-to-object pairing. It is now: a phase record names one
`.rgn` and one `.col`, and for all **11 / 11** pairs the two share a stem and
agree exactly on bounding box and cell size.

| stem | phases | verts / tris |
|---|---|---|
| `test` | 3 | 34 / 60 |
| `mapmesh_box_500km` | 70 | 8 / 12 |
| `S01_AsteroidVolume_wp` | 3 | 111 / 218 |
| `S04_AsteroidVolume_wp` | 2 | 405 / 790 |
| `S05_AsteroidVolume_wp` | 2 | 89 / 174 |
| `S08_p1_AsteroidVolume_wp` | 1 | 134 / 260 |
| `S08_p2_AsteroidVolume_wp` | 1 | 8 / 12 |
| `S13_AsteroidVolume_wp` | 1 | 73 / 134 |
| `S14_p1_AsteroidVolume_wp` | 1 | 502 / 924 |
| `S14_p2_AsteroidVolume_wp` | 1 | 632 / 1 164 |
| `S28_p1_AsteroidVolume_wp` | 1 | 554 / 1 020 |

`_AsteroidVolume_` also says what the meshes *are*: the asteroid fields, which
is why the collision hull is a closed manifold and why most stages need none —
**70 of the 87 phases use `mapmesh_box_500km`**, the bare arena wall.

### The name confirms the decode, and gives the world unit

`mapmesh_box_500km.col` is the object this page decoded as **8 vertices and 12
triangles spanning exactly ±250 000** — a cube. Its name says that cube is
**500 km** across, and the decoded span is **500 000.0** units exactly, so

> **one world unit is one metre.**

This is a name-based inference, but the arithmetic is exact and it runs the
other way as a check on the format work: a wrong stride or index width could not
have produced a box whose measured size matches its own filename.

Reproduce with `tools/re-capture/miscbin_names.py <extract root> [--pairs]`
(recorded in [`../data/miscbin-names.txt`](../data/miscbin-names.txt)).

❔ Still open: the 18 `CollisionSet_*.bin` objects (magic `0x00000810`, and all
**exactly 1 675 148 bytes**, which is odd for per-stage data) are named but not
decoded. And the runtime consumer now has a name — the `.pe` RTTI carries
`CMapColliderBridge` and `CSingleton<CMapColliderBridge>` at offset 9 044 264 —
but has not been followed into the code.