docs: Reorganize objects documentation into modular structure

Split monolithic objects.md into organized subdirectory with focused modules:
- building.md, terrain.md, vegetation.md, structure.md, barrier.md, bridge.md, aeroway.md, water.md, landuse.md, generic.md
- Updated cross-references in data-pipeline.md, contextual.md, elevation-sampler.md, README.md to point to new locations
- Removed version numbers from tech stack links (use latest docs)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: 2 people

README.md

@@ -222,7 +222,7 @@ The `docs/` directory contains 79 comprehensive files organized by topic:
 
 - **[visualization/canvas-rendering.md](docs/visualization/canvas-rendering.md)** — Feature rasterization (9-layer painter's algorithm)
 - **[visualization/ground-surface.md](docs/visualization/ground-surface.md)** — Terrain mesh generation
-- **[visualization/objects.md](docs/visualization/objects.md)** — Buildings, structures, drone
+- **[visualization/objects/README.md](docs/visualization/objects/README.md)** — Buildings, structures, drone
 
 ### Reference
 

docs/data-pipeline.md

@@ -284,7 +284,7 @@ flowchart LR
 - **Contextual data details**: [`data/contextual.md`](data/contextual.md)
 - **Canvas rendering**: [`visualization/canvas-rendering.md`](visualization/canvas-rendering.md)
 - **Ground surface (terrain mesh)**: [`visualization/ground-surface.md`](visualization/ground-surface.md)
-- **3D objects**: [`visualization/objects.md`](visualization/objects.md)
+- **3D objects**: [`visualization/objects/README.md`](visualization/objects/README.md)
 - **Coordinate system**: [`coordinate-system.md`](coordinate-system.md) — geographic → Three.js local tangent plane math
 - **Tile ring system**: [`tile-ring-system.md`](tile-ring-system.md) — ring loading details
 - **Glossary**: [`glossary.md`](glossary.md)

docs/data/contextual.md

@@ -305,7 +305,7 @@ Nine categories of contextual features are parsed and rendered:
 For colors, widths, heights, and detailed rendering specs, see:
 
 - **[Canvas Rendering](../visualization/canvas-rendering.md)** - layer ordering, colors, widths, dash patterns, drawing algorithms
-- **[3D Object Visualization](../visualization/objects.md)** - heights, shapes, geometry, materials, roof types
+- **[3D Object Visualization](../visualization/objects/README.md)** - heights, shapes, geometry, materials, roof types
 
 ## Graceful Degradation
 

docs/data/elevation-sampler.md

@@ -498,7 +498,7 @@ matrix.setPosition(treeX, terrainY + trunkOffset, -treeY);
 
 ### Lifecycle Integration
 
-ElevationSampler is initialized once at app startup and distributed to all mesh factories. It samples terrain elevation when creating 3D feature objects. For complete integration details, see **[3D Object Visualization](../visualization/objects.md#rendering-pipeline)** and **[Ground Surface Rendering](../visualization/ground-surface.md#integration-with-drone-system)**.
+ElevationSampler is initialized once at app startup and distributed to all mesh factories. It samples terrain elevation when creating 3D feature objects. For complete integration details, see **[3D Object Visualization](../visualization/objects/systems.md#rendering-pipeline)** and **[Ground Surface Rendering](../visualization/ground-surface.md#integration-with-drone-system)**.
 
 ### Coordinate System Consistency
 
@@ -536,4 +536,4 @@ This ensures:
 
 - **[Elevation Data System](./elevations.md)** — Terrarium format, tile loading, caching
 - **[Coordinate System](../coordinate-system.md)** — Complete coordinate transformation mapping
-- **[3D Object Visualization](../objects.md)** — How mesh factories use ElevationSampler
+- **[3D Object Visualization](../visualization/objects/README.md)** — How mesh factories use ElevationSampler

docs/visualization/README.md

@@ -4,4 +4,4 @@
 |------|-------------|
 | [ground-surface.md](ground-surface.md) | Two-stage terrain: elevation geometry + contextual canvas texture |
 | [canvas-rendering.md](canvas-rendering.md) | 9-layer painter's algorithm, feature rasterization to 2048×2048 |
-| [objects.md](objects.md) | 3D objects: buildings, vegetation, structures, barriers, bridges |
+| [objects/README.md](objects/README.md) | 3D objects: buildings, vegetation, structures, barriers, bridges |

docs/visualization/objects.md

@@ -0,0 +1,36 @@
+# 3D Object Visualization
+
+## Overview
+
+The simulator visualizes five categories of real-world objects extracted from Overture Maps data. Each type is rendered as 3D geometry in the Three.js scene using specialized mesh factories that transform geographic data into spatial meshes.
+
+**Object Categories:**
+
+1. **Buildings**: Extrusion-based 3D structures with parametric roofs (gabled, hipped, domed, etc.)
+2. **Vegetation**: Distributed trees, forests, shrubs, orchards, and vineyards using instanced mesh for efficiency
+3. **Structures**: Man-made objects like towers, chimneys, water towers, and cranes built from parametric shapes
+4. **Barriers**: Linear features like walls, hedges, and fences extruded along their paths
+5. **Bridges**: Elevated deck segments for roads and railways with layer-based height control
+
+## Object Types
+
+| File | Description |
+|------|-------------|
+| [buildings.md](buildings.md) | Walls, roofs (gabled, hipped, domed, pyramidal, etc.), material colors, height defaults |
+| [vegetation.md](vegetation.md) | Trees, forests, scrub, orchards, vineyards; instanced mesh optimization; per-tree sampling |
+| [structures.md](structures.md) | Towers, chimneys, cranes, water towers; parametric shapes; structure-specific materials |
+| [barriers.md](barriers.md) | Walls, hedges, fences; linear extrusion; segment-based elevation sampling |
+| [bridges.md](bridges.md) | Elevated decks; layer-based height control; road/rail deck width |
+
+## Systems & Architecture
+
+| File | Description |
+|------|-------------|
+| [systems.md](systems.md) | Rendering pipeline, spatial organization, tile ring system, performance optimization |
+
+## See Also
+
+- **[Data Pipeline](../../data-pipeline.md)** — Overview of feature extraction and mesh generation
+- **[Elevation Sampling & Interpolation](../data/elevation-sampler.md)** — Bilinear interpolation for terrain heights
+- **[Coordinate System & Rendering](../coordinate-system.md)** — Geographic to Three.js transformation
+- **[Glossary](../glossary.md)** — Technical terminology

docs/visualization/objects/README.md

@@ -0,0 +1,77 @@
+# Barriers
+
+## Visual Characteristics
+
+Barriers appear as linear features running across the landscape. Walls are thin, tall, and rigid. Hedges are wider, lower, and green. Retaining walls are squat and sturdy. City walls are massive stone structures.
+
+**Examples:**
+- Garden wall: 0.3m wide, 2m tall, beige (#c0b8b0)
+- Hedge: 1m wide, 1.5m tall, dark green (#4a7030)
+- City wall: 2m wide, 6m tall, stone (#c8c0b0)
+- Retaining wall: 0.5m wide, 1.5m tall, gray (#a8a098)
+
+## Data Sources
+
+Barriers identified by Overture fields:
+- `barrier=wall`, `city_wall`, `retaining_wall`, `fence`, `hedge`, `guardrail`
+- `height` tag (in meters)
+- `width` tag (in meters, defaults based on type)
+- `material` tag (brick, concrete, stone, wood, metal) — overrides type color
+- `colour` tag (explicit RGB override)
+
+## Rendering Strategy
+
+**Line Extrusion**: Each LineString segment is converted to a box mesh:
+
+1. For each consecutive pair of coordinates in the LineString:
+   - Compute segment midpoint and length
+   - Calculate rotation angle to align with path
+   - Create `BoxGeometry(width, height, segmentLength)`
+   - Position at midpoint with appropriate rotation
+   - Sample elevation at midpoint
+
+2. **Rotation**: `rotation.y = -angle` where `angle = atan2(dx, dy)` aligns box along path
+
+## Geometry Details
+
+**Box Mesh per Segment:**
+- Dimensions: (width, height, length)
+  - Width: configured per type or tag (0.3m wall, 1m hedge)
+  - Height: configured per type or tag (2m wall, 1.5m hedge)
+  - Length: segment length in Mercator coordinates
+- Material: `MeshLambertMaterial` with type or material-based color
+- Positioning: Centered at segment midpoint, terrain elevation + height/2
+
+**Example (Garden Wall, 50m segment):**
+```
+BoxGeometry(0.3, 2.0, 50)           // 0.3m thick, 2m tall, 50m long
+Position: (midX, terrainY + 1.0, -midY)
+Rotation.y: -angleToAlignWithPath
+Color: #c0b8b0
+```
+
+## Configuration
+
+| Barrier Type | Default Width | Default Height | Default Color |
+|---|---|---|---|
+| wall | 0.3m | 2.0m | #c0b8b0 |
+| city_wall | 2.0m | 6.0m | #c8c0b0 |
+| retaining_wall | 0.5m | 1.5m | #a8a098 |
+| hedge | 1.0m | 1.5m | #4a7030 |
+
+**Material Color Overrides:**
+Same palette as buildings: brick (#c87060), concrete (#c8c4b8), stone (#b8b0a0), wood (#c8a878), metal (#888888), etc.
+
+## Elevation Handling
+
+- **Midpoint sampling**: Elevation sampled at segment midpoint
+- **Vertical positioning**: Height/2 above terrain, so base touches ground
+- **Slope following**: Each segment independently samples elevation, creating stepped appearance on steep terrain
+- **Precision**: Segments reconnect seamlessly across segment boundaries
+
+## See Also
+
+- **[Bridges](bridges.md)** — Linear elevated features
+- **[Structures](structures.md)** — Point-based objects
+- **[Systems](systems.md#spatial-organization)** — Coordinate system and spatial layout
+- **[Data Pipeline](../../data-pipeline.md)** — Feature extraction process

docs/visualization/objects/barriers.md

@@ -0,0 +1,73 @@
+# Bridges
+
+## Visual Characteristics
+
+Bridges appear as elevated flat decks spanning roads and railways. They float above terrain, supported by layer height (vertical separation). Decks are proportionally wider than the underlying road/rail to show structural overhang.
+
+**Examples:**
+- Highway overpass: wide gray deck (#b0a898) elevated 1 layer (5m) above road
+- Railway bridge: thinner deck elevated 2 layers (10m) above terrain
+- Pedestrian bridge: narrow deck at 1 layer height
+
+## Data Sources
+
+Bridges identified by Overture fields:
+- `bridge=yes` on `highway=*` or `railway=*` features
+- `layer=N` (integer, default 1) — vertical separation in multiples of 5m per layer
+- `width` tag for road width, default rail width from `railway=*` type
+- Deck margin: automatically adds 2m on each side of road/rail width
+
+## Rendering Strategy
+
+**Deck Extrusion**: Similar to barriers but simpler — just a flat box at elevated height:
+
+1. For each consecutive pair of coordinates in LineString:
+   - Compute midpoint and length
+   - Calculate rotation angle
+   - Create flat `BoxGeometry(deckWidth, DECK_THICKNESS, segmentLength)` where:
+     - deckWidth = road/rail width + 4m (2m margin per side)
+     - DECK_THICKNESS = 0.5m
+   - Position at terrain elevation + layer × 5m
+
+## Geometry Details
+
+**Deck Mesh per Segment:**
+- Dimensions: (width, 0.5m thickness, length)
+- Width = vehicle width + 4m (represents deck overhang)
+  - Motorway (25m): deck 29m
+  - Railway (4m): deck 8m
+  - Footway (2m): deck 6m
+- Material: Tan/beige Lambert (#b0a898)
+- Positioning: Centered at midpoint, terrain elevation + layer height offset
+
+**Layer Height Calculation:**
+```
+verticalOffset = layer × 5m
+Examples:
+  layer=1: 5m above terrain
+  layer=2: 10m above terrain
+  layer=-1: 5m below terrain (underpass)
+```
+
+## Configuration
+
+| Parameter | Value |
+|---|---|
+| Deck color | #b0a898 (tan, resembles concrete) |
+| Deck thickness | 0.5m |
+| Deck margin | 2m on each side (total +4m to road width) |
+| Layer height multiplier | 5m per layer unit |
+| Default layer | 1 (if not specified) |
+
+## Elevation Handling
+
+- **Base elevation**: Sampled at segment midpoint (same as road/rail below)
+- **Vertical offset**: Added to base elevation based on layer tag
+- **No tilt**: Deck remains horizontal even on slopes (realistic for bridge engineering)
+- **Precision**: Each segment samples independently
+
+## See Also
+
+- **[Barriers](barriers.md)** — Linear ground-level features
+- **[Systems](systems.md#spatial-organization)** — Coordinate system and spatial layout
+- **[Data Pipeline](../../data-pipeline.md)** — Feature extraction process