146 lines
4.8 KiB
Markdown
146 lines
4.8 KiB
Markdown
# Radar Exhibit — Design Document
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## Hardware target
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- Geekom A8 Max: AMD Ryzen 9 8945HS, Radeon 780M (Mesa/RADV), 32 GB RAM
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- Ubuntu 25.10, g++ 15.2.0, C++20, OpenGL 4.3 Core
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---
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## Screen layout
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Three fixed regions rendered with `glViewport` + `glScissor`:
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| Region | Content |
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|--------|---------|
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| Left panel | Text description, control list (white text; red labels; pink keystrokes) |
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| Right panel — upper | Radar scope |
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| Right panel — lower | Status bar: range, bearing, scope ID (yellow text) |
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---
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## Scope sequence (cycled with keys 1 / 2)
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1. Exhibit introduction (text only)
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2. Chain Home A-Scope (1940s)
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3. Marine A-Scope (1940s)
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4. PPI — stationary marine traffic control
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5. PPI — on-board boat
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Each scope's control state is **independent** and **resets on re-entry**.
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---
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## Radar equation
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$$P_r = \frac{P_t G^2 \lambda^2 \sigma}{(4\pi)^3 R^4}$$
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Signal strength falls off with $1/R^4$. Each radar type has fixed hardware loop gain baked into its shader set as a constant.
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---
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## Controls (keyboard until physical panel is built)
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| Key | Action |
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|-----|--------|
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| 1 / 2 | Next / previous scope |
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| 3 / 4 | Intensity down / up |
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| 5 / 6 | Receiver sensitivity down / up |
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| q / w | STC sensitivity down / up |
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| e / r | STC range down / up |
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| t / y | Radiogoniometer left / right (Chain Home only) |
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| u / i | Max range down / up (all except Chain Home) |
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| o / p | Range cursor down / up (PPI only) |
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| a / s | Bearing cursor CCW / CW (PPI only) |
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| d / f | Antenna bearing CCW / CW (Marine A-Scope only) |
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Notes:
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- Radiogoniometer, marine antenna bearing, and PPI bearing cursor share one physical knob on the eventual panel; kept separate in software.
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- Range cursor ≠ max range: max range is the radar's selected range setting; range cursor is the measurement cursor on the PPI display.
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---
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## Scope specifications
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### Chain Home A-Scope
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- Fixed range: 200 miles
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- No graticule; crystal-oscillator range pips every 20 miles (operator cannot change)
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- Bearing via radiogoniometer simulation: operator finds null point; bearing shown as text below scope
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- Two perpendicular antenna sets (N-S, E-W); radiogoniometer angle determines which target pip goes to null
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### Marine A-Scope
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- Ranges: 1.5 / 3.0 / 6.0 / 12.0 miles
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- Range pips: every 0.25 / 0.5 / 1.0 / 2.0 miles respectively (fixed oscillator; not affected by range setting)
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- No graticule
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- Bearing by rotating simulated dish/horn antenna (d/f keys)
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- Pip shape: finite rise, fixed-width pulse, finite fall — curved waveform, not a vertical line
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### PPI scopes (both)
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- 360° sweep with phosphor persistence via FBO (semi-transparent black quad each frame; no full clear)
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- Range cursor and bearing cursor overlay
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#### Stationary (marine traffic control)
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- Fixed observer position; targets move relative to scope center
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#### On-boat
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- Observer is scope center; heading-up display — world rotates as boat heading changes
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- Boat position/heading supplied from GDAL/PostgreSQL data
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---
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## Architecture
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### Class hierarchy (State pattern)
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```
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BaseScope — intensity, sensitivity, STC vars, virtual render/update
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├── AScope — horizontal sweep, curved pip waveform
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│ ├── ChainHomeScope — radiogoniometer, fixed 200 mi range, 20 mi pips
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│ └── MarineAScope — antenna bearing knob, 4 range settings
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└── PPIScope — 360° sweep, FBO persistence, range/bearing cursors
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├── StationaryPPI
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└── OnBoatPPI — heading offset passed into shader
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```
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### Threading model
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| Thread | Responsibility |
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|--------|---------------|
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| Render (main) | OpenGL loop, GLFW input, all `glDraw*` calls — never blocks |
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| Simulation | Polls `target_data` (PostgreSQL) and GDAL; updates shared `std::vector<Target>` under `std::mutex` |
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### FBO phosphor decay
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- Render sweep into FBO each frame
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- Blit FBO to screen
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- Do **not** clear color buffer between frames; draw full-screen quad at very low alpha (~0.05) to decay old sweeps
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### Shader notes
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- GL_DEBUG_OUTPUT + `glDebugMessageCallback` enabled at startup (GPU robustness protocol)
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- No NVIDIA-specific extensions; Mesa/RADV only
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- $1/R^4$ attenuation computed in fragment shader; hardware loop gain is a per-scope `uniform` constant
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---
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## File structure
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```
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new-radar/
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├── CMakeLists.txt
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├── src/ — .cpp source files
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├── include/ — .h/.hpp headers
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│ ├── glad/
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│ └── KHR/
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├── glad/src/ — glad.c (bundled)
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├── shaders/ — .vert / .frag files
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├── data/ — patrol_route.json, etc.
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└── map/
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├── charts_enc/ — ENC .000 and GeoTIFF files
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└── lidar_raw/ — LIDAR zips
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```
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---
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## Database
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- PostgreSQL, database `radar`, user `radar`, password `radar`
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- Table `target_data`: polled by simulation thread for live target positions
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