Add chain home land stuff

CLAUDE.md

@@ -612,9 +612,6 @@ Individual scope informations
    brightness will no longer increase, but there will be a slight blooming of
    the target. 
 
-   This is suggested example psudeo code for the target shader
-   for both the radar equation as well as the blooming
-
    Note that values will change depending on the scope being used (traffic control or boat)
 
    -------------------------------------------------------------------
@@ -783,20 +780,90 @@ PPI Radar Equiation
 
    GROUND TERRAIN AND LIDAR DATA PROCESSING
 
-   Note: Do not do this for the Chain Home Radar. Theu user will heve enough
-   of a challenging dealing with the targets and noise alone.
-
    Note that the following files already exist in the project directory
    in the following:
 
    map
-   map/lidar_raw
-   map/lidar_raw/wa2016_west_dem_J1364939.zip
-   map/lidar_raw/wa2022_nooksack_dem_J1364940.zip
+   map/lidar_processed
    map/charts_enc
    map/charts_enc/US5WA45M.000
    map/charts_enc/n48_w123_1arc_v3.tif
-   
+   map/lidar_raw
+   map/lidar_raw/wa2022_nooksack_dem_J1364940.zip
+   map/lidar_raw/wa2016_west_dem_J1364939.zip
+   map/gebco_for_chain_home
+   map/gebco_for_chain_home/gebco_2026_n52.866_s46.397_w-3.93_e2.784_jpg_hs.jpg
+ 
+   For Chain Home only:
+
+   New file added - 
+     map/gebco_for_chain_home/gebco_2026_n52.866_s46.397_w-3.93_e2.784_jpg_hs.jpg
+
+   The file map/gebco_for_chain_home/gebco_2026_n52.866_s46.397_w-3.93_e2.784_jpg_hs.jpg
+   is a GEBCO hillshaded JPEG. The _hs suffix means "hillshade" — a directional-lighting
+   visual render of the terrain. It is NOT raw elevation data. Pixel color values cannot
+   be directly converted to meters above sea level.
+
+   Bounding box (from filename):
+     North: 52.866 N
+     South: 46.397 N
+     West:  -3.930 E (3.930 W)
+     East:   2.784 E
+
+   RAF Ventnor (50.600 N, -1.183 E) maps to approximately pixel (659, 544)
+   in a 1611x1553 image (top-left origin, Y increases downward).
+
+   UV coordinate formula for a given lat/lon in the shader:
+     u = (longitude - LON_W) / (LON_E - LON_W)
+     v = (LAT_N - latitude)  / (LAT_N - LAT_S)   // v=0 at top
+
+     LAND vs. WATER DISCRIMINATION
+     Since this is a hillshade image without elevation values, land and water must be
+     distinguished by color hue in the fragment shader. Convert the RGB texture sample
+     to HSV and apply these thresholds:
+       Ocean (no echo):  HSV hue approximately 170 to 220 degrees
+       Land  (echo):     HSV hue approximately 50 to 170 degrees
+     These are defined in settings.h as GEBCO_OCEAN_HUE_MIN_DEG and GEBCO_OCEAN_HUE_MAX_DEG
+     so they can be tuned without rewriting shader code.
+
+     Because JPEG compression blurs color at coastline boundaries, apply a small
+     soft transition zone (GEBCO_COAST_BLEND_UV_WIDTH in settings.h) to avoid
+     a hard pixel-boundary artifact at the shoreline.
+
+     COVERAGE NOTE
+     The 200nm range circle from Ventnor extends beyond the image to the north, east,
+     and west. Any radar sample point whose lat/lon falls outside the bounding box
+     should be treated as open ocean (zero land echo). The primary threat axis
+     (English Channel, French coast, Belgian coast) is fully within the image.
+
+     ELEVATION LIMITATION
+     This file provides land/water masking only, not actual terrain height. All land
+     returns use a single fixed amplitude defined in settings.h as
+     CHAIN_HOME_LAND_ECHO_AMPLITUDE. There is no line-of-sight terrain shadowing
+     for Chain Home; the 150 degree floodlight beam and 12m wavelength make
+     fine terrain masking historically irrelevant for this simulation.
+
+     OPTIONAL UPGRADE PATH
+     If higher fidelity is later needed, replace with the raw GEBCO NetCDF grid
+     (GEBCO_2024.nc, freely downloadable from gebco.net). That file provides actual
+     elevation in meters on a 15 arc-second grid and can be loaded as a GL_R32F
+     texture giving real line-of-sight capability.
+
+     SETTINGS.H ENTRIES FOR CHAIN HOME TERRAIN
+     #define CHAIN_HOME_MAP_LAT_N          52.866f
+     #define CHAIN_HOME_MAP_LAT_S          46.397f
+     #define CHAIN_HOME_MAP_LON_W          -3.930f
+     #define CHAIN_HOME_MAP_LON_E           2.784f
+     #define CHAIN_HOME_LAND_ECHO_AMPLITUDE 0.6f   // fraction of max A-scope deflection
+     #define GEBCO_OCEAN_HUE_MIN_DEG        170.0f
+     #define GEBCO_OCEAN_HUE_MAX_DEG        220.0f
+     #define GEBCO_COAST_BLEND_UV_WIDTH     0.003f  // ~1-2 pixels at this resolution
+     #define ENABLE_CHAIN_HOME_TERRAIN      1       // set 0 to suppress land clutter
+
+
+
+   For all except for Chain Home:
+
    This needs to be processed into a fragment shader via ray casting.
 
    Details on files:
@@ -916,6 +983,17 @@ PPI Radar Equiation
       coverage boundaries when compositing the height-map. */
    #define DEBUG_SHOW_LIDAR_COVERAGE  0
   
+=============================================================
+
+Sections still to be worked on:
+
+Details of the Traffic Cop and the PostGres database. These
+two subjects are interrelated and will be discussed later
+
+Details on the simulator will be discussed later.
+
+Details on the relationship between the simulator and the movement of the
+police boat will be discussed later.
 
 ==================================
 
@@ -923,8 +1001,3 @@ End of discussion
 
 ==================================
 
-settings.h file suggestions:
-
-The settings.h file needs to improve variables that the developer may need
-to change for facilitate troubleshooting. Need ability to change amplifier gain,
-radar beam width, antenna, gain, and so on.