Fix OSM multipolygon buildings

.trellis/spec/blender/module-structure.md

@@ -46,7 +46,7 @@
 
 | 模块 | 层 | 职责 |
 |---|---|---|
-| `osm.py` | 纯 | `parse_osm()` 读 OSM XML → (bounds, ways, points)；`Projector` 局部米制投影；`parse_height()`、`tags()` |
+| `osm.py` | 纯 | `parse_osm()` 读 OSM XML → (bounds, ways, points)；building multipolygon relation 会作为 synthetic way 进入 ways；`Projector` 局部米制投影；`parse_height()`、`tags()` |
 | `geom.py` | 纯 | 平面几何全家桶。**输入输出一律是投影后的米**，例外只有 `geometry_rings` / `feature_in_bounds`（收原始 GeoJSON 的经纬度） |
 | `catalog.py` | 纯 | `ROAD_LAYERS`、`MATERIALS`、`road_material_specs()`、`check_layers()` |
 | `mesh.py` | bpy | `MeshBatch`、`make_prism`、`add_roof`、`add_wall_panel`、`add_polyline`、集合管理 |
@@ -104,7 +104,8 @@ def assemble(name, x, y, collection, materials):
 `len(ring) >= 3`，并且建筑要保持原始 OSM footprint 参与相机取景：
 
 ```python
-def assemble(ring, way_id, tag, office_overrides, collection, materials):
+def assemble(ring, way_id, tag, office_overrides, collection, materials,
+             inner_rings=None):
     ...
     return added, industrial_added, ring_pts
 ```
@@ -114,6 +115,36 @@ def assemble(ring, way_id, tag, office_overrides, collection, materials):
 `counts["industrial_count"]`，以及写 `scene["office_override_way_ids"]`。
 模块只负责 prism / roof / windows / bevel / building custom properties。
 
+### Building multipolygon 与 height
+
+`parse_osm()` 会把 `type=multipolygon` 且 relation 自身带 `building=*` 的 relation
+追加为 synthetic way：
+
+```python
+{
+    "id": relation_id,
+    "coords": outer_ring_lon_lat,
+    "inner_coords": [inner_ring_lon_lat, ...],
+    "tags": relation_tags,
+    "source": "relation",
+}
+```
+
+member way 不需要带 building tags；relation-level `height` / `building` 才是事实源。
+`generate_scene.py` 在 `handle_building()` 里把 `inner_coords` 投影后传给
+`building.assemble(..., inner_rings=...)`。`building.py` 用 Blender
+`tessellate_polygon()` 生成带洞的 prism 和 roof；没有 inner rings 时仍走原来的
+`MeshBatch` / `make_prism` 路径。
+
+建筑高度语义：
+
+- relation / way 上有合法显式 `height`：`render_height == height`
+- `building=industrial`：沿用 OSM height / 默认高度
+- 普通 building 没有显式 height 且低于 tall threshold：使用办公楼视觉默认 `11.4m`
+
+不要再把有显式 `height=8` 的普通建筑压成 `11.4m`；用户手工编辑 OSM 高度时，OSM
+tag 是更高优先级的事实。
+
 `roads.py` 是 road layer 装配模块，不拥有图层表或计数：
 
 ```python

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/check.jsonl

@@ -0,0 +1 @@
+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/implement.jsonl

@@ -0,0 +1 @@
+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/prd.md

@@ -0,0 +1,39 @@
+# Fix OSM multipolygon building rendering
+
+## Goal
+
+Fix Blender scene generation so OSM `type=multipolygon` building relations are
+rendered as buildings, and explicit OSM `height` tags are respected for normal
+buildings.
+
+## Requirements
+
+1. Parse OSM multipolygon relations whose relation tags include `building=*`.
+2. Use relation-level tags, including `height`, when generating the building.
+3. Support the common case of closed outer way members and closed inner way
+   members, as seen in nantaizi `relation -65`.
+4. Keep existing way-based building rendering working.
+5. Change building height semantics so an explicit `height` tag controls render
+   height; fallback office default `11.4m` should apply only when height is not
+   explicitly present and the building is not industrial / tall.
+6. Validate only `nantaizi-lake-innovation-valley`.
+
+## Acceptance Criteria
+
+- [x] `parse_osm()` exposes the nantaizi building multipolygon relation as a
+      renderable building feature.
+- [x] Unit tests cover relation-level building tags, outer/inner members, and
+      malformed / incomplete relation members.
+- [x] Existing way-based building parsing tests still pass.
+- [x] A relation building with `height=8` renders at `8m`, not the office
+      fallback `11.4m`.
+- [x] nantaizi Blender generation succeeds and includes the multipolygon
+      building in counts / scene digest.
+- [x] No hanyang validation is required unless requested.
+
+## Notes
+
+- Concrete reproduction in current input:
+  `relation -65` has `building=yes`, `height=8`, `type=multipolygon`, outer way
+  `-2948`, and inner way `-2952`. The member ways carry no building tags, so the
+  current way-only dispatcher skips it.

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/report.md

@@ -0,0 +1,48 @@
+# Multipolygon building fix report
+
+## Root Cause
+
+The edited nantaizi OSM has `relation -65` with:
+
+- `type=multipolygon`
+- `building=yes`
+- `height=8`
+- outer way `-2948`
+- inner way `-2952`
+
+The member ways have no building tags. `parse_osm()` only exposed ways, and
+`generate_scene.py` only dispatched ways, so the relation was skipped.
+
+The height issue had a second cause: ordinary non-industrial buildings below
+`30m` were forced to the office fallback render height `11.4m`, even when OSM
+had an explicit `height`.
+
+## Implemented
+
+- `parse_osm()` now exposes building multipolygon relations as synthetic
+  building features with relation-level tags and `inner_coords`.
+- Open relation member way fragments can be stitched into closed rings; malformed
+  relation leftovers are skipped without aborting parsing.
+- `generate_scene.py` passes projected `inner_rings` to building assembly.
+- `building.py` creates prism and roof meshes with holes using Blender
+  tessellation.
+- Explicit OSM `height` now controls render height. The `11.4m` office fallback
+  applies only when height is not explicit.
+
+## Validation
+
+- `python3 -m unittest discover blender/tests`
+- `npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages blender`
+- `npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages cesium`
+- `node scripts/glb-digest.js outputs/nantaizi-lake-innovation-valley/nantaizi-lake-innovation-valley.glb`
+- `python3 ./.trellis/scripts/task.py validate .trellis/tasks/08-03-fix-osm-multipolygon-buildings`
+- `git diff --check`
+
+Confirmed `Building_-65` in scene and GLB:
+
+- `osm_height=8`
+- `render_height=8`
+- GLB contains `Building_-65`, `Building_-65_Roof`, and
+  `Building_-65_Windows`
+
+User verified the result visually in preview.

.trellis/tasks/08-03-fix-osm-multipolygon-buildings/task.json

@@ -0,0 +1,26 @@
+{
+  "id": "fix-osm-multipolygon-buildings",
+  "name": "fix-osm-multipolygon-buildings",
+  "title": "Fix OSM multipolygon building rendering",
+  "description": "",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-03",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}

blender/generate_scene.py

@@ -730,9 +730,10 @@ def build(args):
         focus_points.extend(ring)
 
     def handle_building(way, tag, ring):
+        inner_rings = [projector.ring(coords) for coords in way.get("inner_coords", [])]
         added, ind_added, ring_pts = _building.assemble(
             ring, str(way["id"]), tag, args["office_overrides"],
-            buildings_c, building_mats)
+            buildings_c, building_mats, inner_rings=inner_rings)
         counts["building_count"] += added
         counts["industrial_count"] += ind_added
         if ring_pts:

blender/osmassets/building.py

@@ -1,17 +1,130 @@
 """Building feature assembly (`building=*`)."""
 
+import bpy
+from mathutils import Vector
+from mathutils.geometry import tessellate_polygon
+
 from osmassets.mesh import MeshBatch, add_roof, add_wall_panel, make_prism
 from osmassets.osm import parse_height
 
 
-def add_details(name, ring, height, industrial, materials, collection):
-    footprint = ring[:-1] if len(ring) > 1 and ring[0] == ring[-1] else ring
-    if len(footprint) < 3:
+def _open_ring(ring):
+    if len(ring) > 1 and ring[0] == ring[-1]:
+        return ring[:-1]
+    return ring
+
+
+def _valid_rings(outer, inner_rings):
+    rings = [_open_ring(outer)]
+    rings.extend(_open_ring(ring) for ring in (inner_rings or []))
+    return [ring for ring in rings if len(ring) >= 3]
+
+
+def _flat_vertices(rings, z):
+    vertices = []
+    for ring in rings:
+        vertices.extend((x, y, z) for x, y in ring)
+    return vertices
+
+
+def _ring_offsets(rings):
+    offsets = []
+    offset = 0
+    for ring in rings:
+        offsets.append(offset)
+        offset += len(ring)
+    return offsets
+
+
+def _tessellated_faces(rings, offset=0, reverse=False):
+    polygons = [[Vector((x, y, 0.0)) for x, y in ring] for ring in rings]
+    faces = []
+    for triangle in tessellate_polygon(polygons):
+        face = tuple(offset + index for index in triangle)
+        faces.append(tuple(reversed(face)) if reverse else face)
+    return faces
+
+
+def _side_faces(rings, offsets, top_offset):
+    faces = []
+    for ring_index, ring in enumerate(rings):
+        offset = offsets[ring_index]
+        for i in range(len(ring)):
+            j = (i + 1) % len(ring)
+            if ring_index == 0:
+                faces.append((offset + i, offset + j,
+                              top_offset + offset + j, top_offset + offset + i))
+            else:
+                # Inner-ring walls face the courtyard / void, opposite to the
+                # outer shell.
+                faces.append((offset + i, top_offset + offset + i,
+                              top_offset + offset + j, offset + j))
+    return faces
+
+
+def make_prism_with_holes(name, outer, inner_rings, base, height, material, collection):
+    rings = _valid_rings(outer, inner_rings)
+    if not rings:
+        return None
+    if len(rings) == 1:
+        return make_prism(name, rings[0], base, height, material, collection)
+
+    base_vertices = _flat_vertices(rings, base)
+    top_vertices = _flat_vertices(rings, base + height)
+    top_offset = len(base_vertices)
+    offsets = _ring_offsets(rings)
+    faces = []
+    faces.extend(_tessellated_faces(rings, reverse=True))
+    faces.extend(_tessellated_faces(rings, offset=top_offset))
+    faces.extend(_side_faces(rings, offsets, top_offset))
+    mesh = bpy.data.meshes.new(name + "Mesh")
+    mesh.from_pydata(base_vertices + top_vertices, [], faces)
+    mesh.materials.append(material)
+    mesh.update()
+    obj = bpy.data.objects.new(name, mesh)
+    collection.objects.link(obj)
+    return obj
+
+
+def add_roof_with_holes(name, outer, inner_rings, z, material, collection):
+    rings = _valid_rings(outer, inner_rings)
+    if not rings:
+        return None
+    if len(rings) == 1:
+        return add_roof(name, rings[0], z, material, collection)
+
+    mesh = bpy.data.meshes.new(name + "_RoofMesh")
+    mesh.from_pydata(_flat_vertices(rings, z), [], _tessellated_faces(rings))
+    mesh.materials.append(material)
+    mesh.update()
+    obj = bpy.data.objects.new(name + "_Roof", mesh)
+    collection.objects.link(obj)
+    return obj
+
+
+def explicit_height(tag):
+    if "height" not in tag:
+        return None
+    return parse_height(tag, None)
+
+
+def render_height(tag, industrial):
+    explicit = explicit_height(tag)
+    source_height = max(3.0, explicit if explicit is not None else parse_height(tag, 12.0))
+    height = source_height if industrial or explicit is not None or source_height >= 30.0 else 11.4
+    return source_height, height
+
+
+def add_details(name, ring, height, industrial, materials, collection, inner_rings=None):
+    footprints = _valid_rings(ring, inner_rings)
+    if not footprints:
         return
     glass_mat = materials["factory_glass"] if industrial else materials["glass"]
 
     glass_batch = MeshBatch(name + "_Windows", collection, glass_mat)
-    edges = list(zip(footprint, footprint[1:] + footprint[:1]))
+    edges = []
+    for footprint in footprints:
+        edges.extend(zip(footprint, footprint[1:] + footprint[:1]))
     if industrial:
         band_height = min(1.8, max(0.75, height * 0.16))
         band_base = max(0.9, height * 0.52)
@@ -31,15 +144,15 @@ def add_details(name, ring, height, industrial, materials, collection):
     glass_batch.finish()
 
 
-def assemble(ring, way_id, tag, office_overrides, collection, materials):
+def assemble(ring, way_id, tag, office_overrides, collection, materials,
+             inner_rings=None):
     industrial = (tag.get("building") == "industrial" and
                   way_id not in office_overrides)
-    source_height = max(3.0, parse_height(tag, 12.0))
-    height = source_height if industrial or source_height >= 30.0 else 11.4
+    source_height, height = render_height(tag, industrial)
     material = materials["industrial"] if industrial else materials["default"]
     building_name = "Building_" + way_id
-    building_obj = make_prism(building_name, ring, 0.08, height,
-                              material, collection)
+    building_obj = make_prism_with_holes(
+        building_name, ring, inner_rings, 0.08, height, material, collection)
     if building_obj:
         building_obj["osm_height"] = source_height
         building_obj["render_height"] = height
@@ -51,6 +164,8 @@ def assemble(ring, way_id, tag, office_overrides, collection, materials):
         bevel.segments = 2
     roof_mat = (materials["industrial_roof"] if industrial
                 else materials["office_roof"])
-    add_roof(building_name, ring, height + 0.095, roof_mat, collection)
-    add_details(building_name, ring, height, industrial, materials, collection)
+    add_roof_with_holes(building_name, ring, inner_rings, height + 0.095,
+                        roof_mat, collection)
+    add_details(building_name, ring, height, industrial, materials, collection,
+                inner_rings=inner_rings)
     return 1, int(industrial), ring

blender/osmassets/osm.py

@@ -7,11 +7,62 @@ import math
 import xml.etree.ElementTree as ET
 
 
+def _element_id(element):
+    return element.attrib.get("id", "")
+
+
 def tags(element):
     return {t.attrib.get("k", ""): t.attrib.get("v", "")
             for t in element.findall("tag")}
 
 
+def _coords_from_refs(refs, nodes):
+    return [nodes[r] for r in refs if r in nodes]
+
+
+def _open_ring(coords):
+    if len(coords) > 1 and coords[0] == coords[-1]:
+        return coords[:-1]
+    return coords
+
+
+def _is_closed_ring(coords):
+    return len(coords) >= 4 and coords[0] == coords[-1] and len(_open_ring(coords)) >= 3
+
+
+def _join_member_rings(members):
+    """Build closed rings from relation member coordinate runs.
+
+    Handles the common OSM multipolygon cases: members are either already
+    closed ways, or open way fragments whose endpoints can be stitched together.
+    Malformed leftovers are dropped rather than aborting the whole import.
+    """
+    rings = []
+    pending = [list(member) for member in members if len(member) >= 2]
+    while pending:
+        ring = pending.pop(0)
+        changed = True
+        while not _is_closed_ring(ring) and changed:
+            changed = False
+            for index, candidate in enumerate(pending):
+                if ring[-1] == candidate[0]:
+                    ring.extend(candidate[1:])
+                elif ring[-1] == candidate[-1]:
+                    ring.extend(reversed(candidate[:-1]))
+                elif ring[0] == candidate[-1]:
+                    ring = candidate[:-1] + ring
+                elif ring[0] == candidate[0]:
+                    ring = list(reversed(candidate[1:])) + ring
+                else:
+                    continue
+                pending.pop(index)
+                changed = True
+                break
+        if _is_closed_ring(ring):
+            rings.append(ring)
+    return rings
+
+
 def parse_osm(path):
     root = ET.parse(path).getroot()
     bounds_node = root.find("bounds")
@@ -37,6 +88,7 @@ def parse_osm(path):
             continue
 
     ways = []
+    way_coords_by_id = {}
     for way in root.findall("way"):
         if way.attrib.get("action") == "delete":
             continue
@@ -46,17 +98,53 @@ def parse_osm(path):
                 refs.append(int(ref.attrib["ref"]))
             except (KeyError, ValueError):
                 pass
-        coords = [nodes[r] for r in refs if r in nodes]
+        coords = _coords_from_refs(refs, nodes)
+        way_id = _element_id(way)
         if len(coords) >= 2:
-            ways.append({"id": way.attrib.get("id", ""),
-                         "coords": coords, "tags": tags(way)})
+            way_coords_by_id[way_id] = coords
+        way_tags = tags(way)
+        if len(coords) >= 2:
+            ways.append({"id": way_id, "coords": coords, "tags": way_tags})
+    for relation in root.findall("relation"):
+        if relation.attrib.get("action") == "delete":
+            continue
+        relation_tags = tags(relation)
+        if relation_tags.get("type") != "multipolygon" or "building" not in relation_tags:
+            continue
+        outer_members = []
+        inner_members = []
+        for member in relation.findall("member"):
+            if member.attrib.get("type") != "way":
+                continue
+            coords = way_coords_by_id.get(member.attrib.get("ref", ""))
+            if not coords:
+                continue
+            role = member.attrib.get("role", "")
+            if role == "inner":
+                inner_members.append(coords)
+            elif role in ("", "outer"):
+                outer_members.append(coords)
+        outer_rings = _join_member_rings(outer_members)
+        if not outer_rings:
+            continue
+        inner_rings = _join_member_rings(inner_members)
+        relation_id = _element_id(relation)
+        for index, outer in enumerate(outer_rings):
+            synthetic_id = relation_id if len(outer_rings) == 1 else f"{relation_id}:{index + 1}"
+            ways.append({
+                "id": synthetic_id,
+                "coords": outer,
+                "inner_coords": inner_rings,
+                "tags": relation_tags,
+                "source": "relation",
+            })
     return bounds, ways, point_features
 
 
 def parse_height(feature_tags, default):
     try:
         return max(0.5, float(feature_tags.get("height", default)))
-    except ValueError:
+    except (TypeError, ValueError):
         return default
 
 

blender/tests/test_pure.py

@@ -356,6 +356,90 @@ class ParseOsmTest(unittest.TestCase):
             os.unlink(handle.name)
 
 
+class ParseOsmMultipolygonTest(unittest.TestCase):
+    def parse_text(self, text):
+        handle = tempfile.NamedTemporaryFile("w", suffix=".osm", delete=False,
+                                             encoding="utf-8")
+        handle.write(text)
+        handle.close()
+        try:
+            return parse_osm(handle.name)
+        finally:
+            os.unlink(handle.name)
+
+    def test_building_relation_uses_relation_tags_and_members(self):
+        _, ways, _ = self.parse_text("""<?xml version='1.0' encoding='UTF-8'?>
+<osm version='0.6'>
+  <bounds minlon='114.0' minlat='30.0' maxlon='114.01' maxlat='30.01'/>
+  <node id='1' lon='114.001' lat='30.001'/>
+  <node id='2' lon='114.004' lat='30.001'/>
+  <node id='3' lon='114.004' lat='30.004'/>
+  <node id='4' lon='114.001' lat='30.004'/>
+  <node id='5' lon='114.002' lat='30.002'/>
+  <node id='6' lon='114.003' lat='30.002'/>
+  <node id='7' lon='114.003' lat='30.003'/>
+  <node id='8' lon='114.002' lat='30.003'/>
+  <way id='outer'><nd ref='1'/><nd ref='2'/><nd ref='3'/><nd ref='4'/><nd ref='1'/></way>
+  <way id='inner'><nd ref='5'/><nd ref='6'/><nd ref='7'/><nd ref='8'/><nd ref='5'/></way>
+  <relation id='65'>
+    <member type='way' ref='outer' role='outer'/>
+    <member type='way' ref='inner' role='inner'/>
+    <tag k='type' v='multipolygon'/>
+    <tag k='building' v='yes'/>
+    <tag k='height' v='8'/>
+  </relation>
+</osm>
+""")
+        relation_buildings = [way for way in ways if way["id"] == "65"]
+        self.assertEqual(len(relation_buildings), 1)
+        building = relation_buildings[0]
+        self.assertEqual(building["tags"]["building"], "yes")
+        self.assertEqual(building["tags"]["height"], "8")
+        self.assertEqual(building["source"], "relation")
+        self.assertEqual(len(building["coords"]), 5)
+        self.assertEqual(len(building["inner_coords"]), 1)
+        self.assertEqual(len(building["inner_coords"][0]), 5)
+
+    def test_open_outer_members_are_stitched(self):
+        _, ways, _ = self.parse_text("""<?xml version='1.0' encoding='UTF-8'?>
+<osm version='0.6'>
+  <bounds minlon='114.0' minlat='30.0' maxlon='114.01' maxlat='30.01'/>
+  <node id='1' lon='114.001' lat='30.001'/>
+  <node id='2' lon='114.004' lat='30.001'/>
+  <node id='3' lon='114.004' lat='30.004'/>
+  <node id='4' lon='114.001' lat='30.004'/>
+  <way id='a'><nd ref='1'/><nd ref='2'/><nd ref='3'/></way>
+  <way id='b'><nd ref='3'/><nd ref='4'/><nd ref='1'/></way>
+  <relation id='66'>
+    <member type='way' ref='a' role='outer'/>
+    <member type='way' ref='b' role='outer'/>
+    <tag k='type' v='multipolygon'/>
+    <tag k='building' v='yes'/>
+  </relation>
+</osm>
+""")
+        building = [way for way in ways if way["id"] == "66"][0]
+        self.assertEqual(len(building["coords"]), 5)
+        self.assertEqual(building["coords"][0], building["coords"][-1])
+
+    def test_incomplete_relation_member_is_skipped_not_fatal(self):
+        _, ways, _ = self.parse_text("""<?xml version='1.0' encoding='UTF-8'?>
+<osm version='0.6'>
+  <bounds minlon='114.0' minlat='30.0' maxlon='114.01' maxlat='30.01'/>
+  <node id='1' lon='114.001' lat='30.001'/>
+  <node id='2' lon='114.004' lat='30.001'/>
+  <way id='broken'><nd ref='1'/><nd ref='2'/></way>
+  <relation id='67'>
+    <member type='way' ref='broken' role='outer'/>
+    <member type='way' ref='missing' role='outer'/>
+    <tag k='type' v='multipolygon'/>
+    <tag k='building' v='yes'/>
+  </relation>
+</osm>
+""")
+        self.assertEqual([way["id"] for way in ways], ["broken"])
+
+
 class TagsTest(unittest.TestCase):
     def test_reads_key_value_children(self):
         import xml.etree.ElementTree as ET

docs/changelog.md

@@ -2,6 +2,12 @@
 
 ## 2026-08-03
 
+- 修复 OSM `type=multipolygon` building relation 不渲染的问题：`parse_osm()` 现在会把
+  relation-level `building=*` 合成为可分发的 building feature，并保留 `inner` 成员供
+  `building.py` 用 Blender tessellation 生成带洞 prism / roof。nantaizi 当前
+  `relation -65`（outer `-2948`、inner `-2952`、`height=8`）已进入 Blender/Cesium
+  产物，GLB extras 为 `osm_height=8` / `render_height=8`。同时调整普通建筑高度语义：
+  有显式 `height` 时尊重 OSM；没有显式高度时才使用办公楼默认 `11.4m`。
 - 新增显式 `compress` 阶段与 `scripts/compress-glb.js`，用于从已有 Cesium GLB 生成并列
   WebP 压缩产物，不进入 `all`，不覆盖默认 `<area-id>.glb`。nantaizi 试验结果：
   `20.50 MB -> 4.80 MB`，embedded images `17.72 MB -> 2.04 MB`，nodes / meshes /