add additions to claude.md

DESIGN.md

@@ -187,13 +187,25 @@ src/
   simulator.h / simulator.cpp
   knob_panel.h / knob_panel.cpp
   rpi_receiver.h / rpi_receiver.cpp
+  db_panel.h / db_panel.cpp          — Dear ImGui database management panel
+                                       (active only when --database flag passed;
+                                        no radar rendering in this mode)
   settings.h                             — all tunable constants (no .cpp needed)
 
+  imgui/                             — Dear ImGui source, compiled into project
+    imgui.h / imgui.cpp
+    imgui_impl_glfw.h / imgui_impl_glfw.cpp
+    imgui_impl_opengl3.h / imgui_impl_opengl3.cpp
+    imgui_draw.cpp / imgui_tables.cpp / imgui_widgets.cpp
+
 shaders/
   phosphor.vert / phosphor.frag      — parameterized for P1 and P7 via uniforms
   graticule.vert / graticule.frag
   text.vert / text.frag
   sweep.vert / sweep.frag
+  bloom.vert / bloom.frag            — two-pass bloom: render to FBO, Gaussian
+                                       blur bright spots, blend back; used for
+                                       target blooming from radar equation output
 ```
 
 ---
@@ -342,3 +354,51 @@ No raw `new` or `delete` anywhere in the codebase. No `malloc`/`free`.
    are blocked during the animation. The new range value is latched when the
    key is pressed but not applied to the scope state until SLIDING_IN completes.
    Animation duration is approximately 0.5 seconds per slide (out and in).
+
+12. **All dimensions are stored and computed in meters** throughout the system.
+   Any incoming data from Raspberry Pi receivers or the simulator that arrives in
+   feet (e.g., altitude from ADS-B in feet, antenna heights) is converted to
+   meters at the boundary in `RPiReceiver::parseFrame()` or `Simulator::poll()`
+   before the value enters any shared data structure. No feet values appear
+   anywhere inside the system after the conversion point.
+   Conversion: 1 foot = 0.3048 meters exactly.
+
+13. **Default target dimensions** used when a target is first seen with no
+   database record. All values in meters. `need_update` is set TRUE for all
+   defaults so the operator knows to fill in real data.
+
+   | Category      | Length (m) | Fuselage/Beam width (m) | Material    |
+   |---|---|---|---|
+   | GA aircraft   | 4.0        | 1.0                     | aluminum    |
+   | Commercial a/c| 30.0       | 5.0                     | aluminum    |
+   | AIS vessel    | 20.0       | 5.0                     | steel       |
+   | Simulator boat| 6.0        | 2.0                     | fiberglass  |
+
+   AIS-sourced vessels default to steel (legally required commercial traffic).
+   Simulator-sourced boats default to fiberglass (small pleasure craft).
+   Aircraft source type does not disambiguate GA vs. commercial — the system
+   defaults to GA and lets the operator correct it.
+
+14. **Bloom post-processing** uses a dedicated `bloom.vert` / `bloom.frag` shader
+   pair. The pipeline is: render targets to an offscreen FBO at full computed
+   brightness (from radar equation output), apply a two-pass Gaussian blur to
+   pixels above a luminance threshold, then additively blend the blurred result
+   back onto the main framebuffer. Bloom threshold and blur radius are
+   `constexpr` constants in `settings.h`.
+
+15. **Dear ImGui** is used for the database management panel, activated by the
+   `--database` command-line flag. In that mode no radar rendering occurs —
+   main.cpp skips the scope/shader initialization path entirely and starts the
+   ImGui loop instead. ImGui source files live under `src/imgui/` and are
+   compiled directly into the project (no separate install step). The panel
+   provides: a scrollable target table with `need_update` highlighted, inline
+   edit fields for length/width/height/material, a dropdown for target type,
+   and a Save button that writes to PostgreSQL via libpq.
+
+16. **Chain Home RCS resonance** is modelled with a multiplier constant
+   `CHAIN_HOME_RCS_RESONANCE_FACTOR` in `settings.h`. At 30 MHz (λ ≈ 10 m),
+   aircraft with wingspans of 10–30 m are in the Mie/resonant scattering
+   region; RCS can be 2–5× the geometric cross section. The default value is
+   3.0 (a mid-range estimate). This is applied in the radar equation computation
+   for Chain Home targets only, before the result is passed to the bloom/
+   brightness pipeline.