Ensure proper operation of land and buildings

CLAUDE.md

@@ -215,9 +215,10 @@ should be articulated in the descriptive text
       Let's assign key . for toggling between 25 and 12.5 PRF. There is no range selection. 
       Note on description; this is to reduce  use of the shift key.
 
-      Because of the slow repetition rate, the phosphor used was an early implementation
-      of the p7 phosphor so that the targets will still glow between the sweeps and not cause
-      flickering.
+      Because of the slow repetition rate, the phosphor used was P2 (long-persistence green)
+      so that the targets will still glow between the sweeps and not cause flickering. P2 is
+      a single-layer green phosphor with longer decay than P1, appropriate for an A-scope at
+      low PRF. Unlike P7, it does not produce a blue flash or a seconds-long smearing tail.
 
       Another unique feature would be a response to the drifting problem in early electronics. 
       The scope electronics would use a crystal calibrator that puts tiny pips or spikes at
@@ -235,7 +236,23 @@ should be articulated in the descriptive text
            presentation. All are P7 phosphor. Immediate strike by the electron beam is blue.
            persistence is green/yellow. Targets, range rings, and range ring labels shall all
            persist and fade out together. They should be faded out by the time the sweep
-           to that location. 
+           returns to that location.
+
+           IMPORTANT — range rings are beam-painted, not a static overlay:
+           Range rings and their labels are written by the rotating sweep beam on
+           each pass, exactly like target echoes. They are NOT rendered as a fixed
+           overlay on top of the scope. This means they are fully subject to P7
+           persistence and decay just as targets are.
+
+           When the operator changes max range (u/d keys), the new ring geometry
+           takes effect only for the sector the sweep is currently painting. The
+           rest of the scope still holds the old ring positions in the phosphor,
+           glowing and fading normally. As the sweep continues rotating, each
+           sector it reaches is repainted with the new ring geometry, replacing the
+           old. One full sweep rotation after the change, the transition is complete
+           and only the new rings remain. This is physically correct — the phosphor
+           holds whatever the beam last wrote. No special transition animation is
+           needed; the behavior emerges naturally from the phosphor model.
 
            The maximum range settings are 6 miles for the marine radar scope 
            Rings should be 2,4, and 6 miles for marine.
@@ -619,7 +636,7 @@ AScope : public Scope (abstract) — shared A-scope behavior:
   - Noise floor rendering (rain/wave clutter)
   - Incandescent graticule (three horizontal amplitude lines + vertical range lines)
   - Bearing control with key-hold acceleration
-  - Phosphor type as parameter (P1 or P7)
+  - Phosphor type as parameter (P1, P2, or P7)
 
 MarineAScope : public AScope
   - P1 phosphor (green)
@@ -630,7 +647,7 @@ MarineAScope : public AScope
     u and d ignored during graticule swap animation
 
 ChainHomeAScope : public AScope
-  - P7 phosphor (early implementation)
+  - P2 phosphor (long-persistence green)
   - Goniometer state: H/V mode toggle, azimuth angle, elevation angle
   - PRF toggle: 25 Hz / 12.5 Hz
   - Calibrator stretch/shrink scale factor
@@ -644,6 +661,11 @@ PPIScope : public Scope (abstract) — shared PPI behavior:
   - Cursor range/bearing readout under scope (white text)
   - Bearing offset for boat mode (k/j)
   - Cursor range clamped to max range
+  - Range rings and labels are beam-painted per sweep sector, NOT a static overlay;
+    the sweep shader evaluates ring radii for the CURRENT max range at the moment
+    each beam angle is rendered; the phosphor buffer retains whatever was last
+    written, so old ring positions fade naturally as the sweep overwrites them with
+    new geometry — no special transition code required
 
 MarinePPIScope : public PPIScope
   - Sweep time: 4 seconds
@@ -735,7 +757,8 @@ settings.h — tunable constants:
   includes settings.h. No values are hardcoded elsewhere.
   Categories planned:
     - Phosphor P1 color
-    - Phosphor P7 strike color, persistence color, decay times (PPI and Chain Home)
+    - Phosphor P2 color and decay time (Chain Home A-Scope)
+    - Phosphor P7 strike color, persistence color, decay times (PPI scopes and PAR)
     - Sweep line width, brightness, fade trail, periods per scope
     - PAR scan rate; Chain Home PRF high and low
     - Graticule incandescent color, line widths
@@ -1459,11 +1482,24 @@ TERRAIN PREPROCESSING
 
 ==================================================================
 
-The raw LiDAR zip files cannot be used at exhibit runtime. The offline
-tool terrain_preprocess processes them once and writes ready-to-use
-binary grids to map/lidar_processed/. Must be run before first launch
-and re-run whenever TERRAIN_BBOX_* or TERRAIN_PROCESSED_CELL_DEG
-constants in settings.h change.
+All three raw terrain sources are processed in a single pass by the
+offline tool terrain_preprocess, which writes ready-to-use binary grids
+to map/lidar_processed/. Must be run before first launch and re-run
+whenever TERRAIN_BBOX_* or TERRAIN_PROCESSED_CELL_DEG constants in
+settings.h change.
+
+Sources processed:
+  map/charts_enc/n48_w123_1arc_v3.tif         — USGS 1 arc-second DEM
+                                                 (~30 m); already WGS84;
+                                                 covers full ATC radar range
+                                                 including distant ridges
+  map/lidar_raw/wa2016_west_dem_J1364939.zip   — 2016 LiDAR DEM (~1 m);
+                                                 projected; requires warp
+  map/lidar_raw/wa2022_nooksack_dem_J1364940.zip — 2022 LiDAR DEM (~1 m);
+                                                 projected; requires warp
+  map/charts_enc/US5WA45M.000                  — S-57 ENC; material
+                                                 classification only; no
+                                                 elevation data
 
 TOOL
   Build target:  terrain_preprocess  (separate CMake executable)
@@ -1472,16 +1508,22 @@ TOOL
   Run:           ./terrain_preprocess   (from build directory)
 
 PIPELINE (runs in order)
-  1. Unzip both LiDAR archives to a temp directory.
-  2. Inventory tiles — enumerate .tif / .img files, check CRS and
-     native resolution of each.
-  3. Merge tiles within each survey into a GDAL VRT mosaic.
-  4. Warp both surveys to WGS84 (EPSG:4326) at
-     TERRAIN_PROCESSED_CELL_DEG resolution.
-  5. Crop to bounding box: TERRAIN_BBOX_LAT_MIN/MAX,
-     TERRAIN_BBOX_LON_MIN/MAX.
-  6. Merge the two surveys — where they overlap, the 2022 Nooksack
-     data wins over the 2016 western data (higher vintage / resolution).
+  1. Open USGS DEM (n48_w123_1arc_v3.tif) directly via GDAL — already
+     in WGS84, no warp needed. Crop to TERRAIN_BBOX_LAT/LON bounds.
+  2. Unzip both LiDAR archives to a temp directory.
+  3. Inventory LiDAR tiles — enumerate .tif / .img files, check CRS
+     and native resolution of each survey.
+  4. Merge tiles within each LiDAR survey into a GDAL VRT mosaic.
+  5. Warp both LiDAR surveys to WGS84 (EPSG:4326) at
+     TERRAIN_PROCESSED_CELL_DEG resolution. Crop to bounding box.
+  6. Three-way elevation merge — priority order, highest to lowest:
+       LiDAR 2022 (Nooksack survey)  — highest resolution, newest vintage
+       LiDAR 2016 (western survey)   — fills gaps in 2022 coverage
+       USGS DEM (1 arc-second)       — floor; covers full extent of all
+                                       radar scopes including distant
+                                       terrain beyond LiDAR coverage
+                                       (Cascades, far ridges for ATC shadow)
+       Any cell with no data from any source → elevation 0.0 m (water).
   7. Material classification:
        Load S-57 ENC (US5WA45M.000) via GDAL/OGR.
        Apply classification rules described in TERRAIN section above.
@@ -1500,7 +1542,8 @@ PIPELINE (runs in order)
        shadow_boat_NNN.u8        uint8 visibility masks for boat waypoints;
                                  NNN = zero-padded waypoint index
        terrain_meta.json         grid dimensions, lat/lon origin, cell size,
-                                 source file checksums, processing date,
+                                 checksums for all three source files,
+                                 processing date,
                                  boat mask waypoint lat/lon list
 
 RUNTIME VALIDATION
@@ -1522,8 +1565,8 @@ OUTPUT FILES (map/lidar_processed/)
                               waypoint lat/lon list used for nearest-mask lookup
 
   These files are the only terrain inputs at runtime.
-  The raw zip archives in map/lidar_raw/ are never opened by
-  the exhibit binary.
+  The raw source files in map/lidar_raw/ and map/charts_enc/ are
+  never opened by the exhibit binary.
 
 ==================================================================