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Adding land features including lidar

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Mark Allyn
2026-04-21 20:00:11 -07:00
parent 2396f94879
commit 8f052b6595
4 changed files with 600 additions and 3 deletions
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249
CLAUDE.md
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@@ -8,7 +8,7 @@ with AMD AI chip R9-8945HS with 32 GB ram
# Project: C++ OpenGL Radar Simulation
**Environment:** Ubuntu Linux (Remote SSH from Windows)
**Tech Stack:** C++20, OpenGL 3.3 Core, GLFW, GLAD, FreeType
**Tech Stack:** C++20, OpenGL 3.3 Core, GLFW, GLAD, FreeType, GDAL (libgdal-dev)
The operating system is Linux (Ubuntu)
@@ -51,6 +51,15 @@ entire directory list is /home/maallyn/new-radar on the Geekom.
./LICENSE
./src
./src/CLAUDE.md
./map
./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
==================================================================
@@ -641,6 +650,16 @@ settings.h — tunable constants:
- Rain clutter filter: default (0.0 = off), minimum (0.0), maximum (1.0), keyboard step size
- Wave clutter filter: default (0.0 = off), minimum (0.0), maximum (1.0), keyboard step size
- Key-hold acceleration for gain, rain clutter, and wave clutter keys
- Terrain bounding box (lat/lon min/max) and processed cell size
- Terrain material σ° values (soil, rock, concrete, water calm/rough)
- Terrain material speckle/grain amplitudes (soil, rock, concrete)
- Terrain classification thresholds (rock elevation, rock slope)
- Terrain polar grid dimensions (range bins, bearing bins)
- Terrain clutter brightness scale for marine PPI
- Terrain boat recompute threshold (degrees bearing offset change)
- ATC terrain clutter suppressed flag (bool, default true)
- ATC terrain shadow enabled flag (bool, default true)
- LiDAR structure height threshold for man-made classification
==================================================================
@@ -1055,6 +1074,220 @@ in settings.h so they can be tuned without touching equation code.
==================================================================
TERRAIN AND LAND CLUTTER
==================================================================
DATA SOURCES
map/charts_enc/US5WA45M.000
S-57 Electronic Navigational Chart; coastline polygon,
pier/breakwater geometry, named landmarks. Parsed with GDAL/OGR.
map/charts_enc/n48_w123_1arc_v3.tif
USGS 1 arc-second (~30 m) DEM GeoTIFF. Terrain elevation for the
Bellingham area — Cascades, Chuckanut Mountain, coastal lowlands.
map/lidar_raw/wa2016_west_dem_J1364939.zip
2016 western WA LiDAR DEM. Resolves waterfront structures,
breakwaters, piers, Boulevard Park boardwalk, and other man-made
features at ~1 m resolution.
map/lidar_raw/wa2022_nooksack_dem_J1364940.zip
2022 Nooksack basin LiDAR DEM. Covers the delta and lowlands
northeast of Bellingham Bay; used for terrain shadowing from the
northeast quadrant.
All three sources are processed offline by terrain_preprocess into
binary grids in map/lidar_processed/. The raw files are never opened
at exhibit runtime. See TERRAIN PREPROCESSING section below.
GDAL (libgdal-dev) is a required build dependency for
terrain_preprocess. It is NOT linked into the main radar binary.
CLASSES
TerrainMap (Thread 1, read-only after init)
Loaded once at startup from map/lidar_processed/. Reads the four
binary grids and the metadata JSON. Provides:
- Elevation query by lat/lon
- Material query by lat/lon
- Pre-computed polar clutter grid (range × bearing bins) per
fixed radar location
- Line-of-sight shadow mask per radar location
Thread 1 only after init; no mutex required.
LandClutter (Thread 1)
Queries TerrainMap to generate clutter returns for each scope.
Called once per full sweep rotation, not once per frame.
- Marine A-Scope: produces amplitude samples along the current
antenna bearing for injection into the range trace.
- Marine PPI / ATC PPI: produces a polar texture (range × bearing)
uploaded to the GPU once per sweep period.
TERRAIN MATERIALS AND RCS
Each terrain cell is classified as one of four materials. Normalized
backscatter coefficient σ° (linear, m²/m²) is defined in settings.h:
TERRAIN_SIGMA0_SOIL ~0.010 (−20 dB) — moist vegetated soil
TERRAIN_SIGMA0_ROCK ~0.032 (−15 dB) — exposed rock, rough face
TERRAIN_SIGMA0_CONCRETE ~0.100 (−10 dB) — smooth hard surface;
structures produce
corner-reflector effect
TERRAIN_SIGMA0_WATER_CALM ~0.0003 (−35 dB) — open water, calm;
mostly specular, low
backscatter
TERRAIN_SIGMA0_WATER_ROUGH ~0.010 (−20 dB) — choppy sea, sea clutter
Classification rules applied by terrain_preprocess at build time:
- Below sea level or inside S-57 coastline polygon → water
- Inside S-57 pier/breakwater/wharf feature → concrete
- Elevation > TERRAIN_ROCK_THRESHOLD_M AND slope
> TERRAIN_ROCK_SLOPE_THRESHOLD_DEG → rock
- All remaining land cells → soil
RADAR EQUATION FOR TERRAIN (area-extensive / clutter form)
P_r = (P_t × G² × λ² × σ° × A_cell) / ((4π)³ × R⁴)
A_cell is the terrain cell area projected along the beam.
Evaluated CPU-side in LandClutter for each illuminated cell.
Result drives per-cell brightness in the clutter texture.
Same radar parameters (P_t, G, λ) used for point targets.
SHADOW / LINE-OF-SIGHT MASKING
Computed by terrain_preprocess for each fixed radar location and
stored in the processed data as uint8 shadow masks. Algorithm: march
outward from the radar along each azimuth radial, tracking the maximum
elevation angle seen. Any cell whose surface angle falls below that
maximum is shadowed — clutter amplitude = 0 and target returns through
that cell are attenuated proportionally.
Shadow masks stored per radar location:
map/lidar_processed/shadow_marine.u8 — marine bay platform
map/lidar_processed/shadow_atc.u8 — BLI ATC tower
Bearing offset (k/j keys on PPI scopes):
The k/j keys change display heading only — which direction appears
at the top of the scope. They do NOT move the radar geographically.
The shadow mask is unchanged. The terrain clutter shader receives
the offset as a rotation uniform and samples the polar texture at
the offset angle. Zero CPU overhead; no shadow recomputation.
Future boat scenario (not in v1):
If the radar antenna physically moves to a new lat/lon, the shadow
mask would be recomputed on a background thread while the display
continues with the previous mask.
PER-SCOPE TERRAIN BEHAVIOR
Marine A-Scope:
Land returns appear as stable blips at fixed ranges on the current
antenna bearing. Concrete structures give strong returns; soil/hills
give moderate returns; shadowed areas return nothing. Period
operators were trained to discard stable blips when searching for
moving targets.
Marine PPI (fixed platform and boat heading offset):
Land clutter is fully visible. Coastline, hills, piers, and
breakwaters paint exactly as on a real period marine radar. The
clutter texture updates once per 4-second sweep rotation.
ATC PPI:
Moving Target Indicator (MTI) cancellation suppresses land clutter.
Controlled by ATC_TERRAIN_CLUTTER_SUPPRESSED (default true) in
settings.h. Terrain shadowing of aircraft IS applied — controlled
by ATC_TERRAIN_SHADOW_ENABLED (default true). Aircraft approaching
behind a ridge appear at reduced amplitude or disappear until they
clear the ridge, as on period ASR equipment.
Chain Home A-Scope:
No terrain data applied. The exhibit scenario faces the English
Channel; the transmitter floodlights the sea. Land returns are
not simulated for this scope.
PAR:
No terrain clutter. PAR points at a single fixed approach path;
the narrow beam and short range make land returns negligible.
TERRAIN CLUTTER SHADER
terrain_clutter.vert / terrain_clutter.frag
Renders the polar clutter texture as a quad overlay on the PPI
scope. Converts screen coordinates to polar, samples the clutter
texture, and outputs P7-compatible phosphor color and alpha so
terrain returns decay on the same timescale as target echoes.
Uniforms:
u_bearingOffsetDeg — boat heading correction (default 0.0)
u_clutterSuppressed — bool; 1 = suppress (ATC mode)
u_maxRangeM — current scope max range in meters
u_clutterBrightness — TERRAIN_MARINE_CLUTTER_BRIGHTNESS scale
Used by MarinePPIScope and ATCPPIScope.
==================================================================
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.
TOOL
Build target: terrain_preprocess (separate CMake executable)
Source: src/terrain_preprocess.cpp
Links: GDAL only; NOT linked into the main radar binary
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).
7. Material classification:
Load S-57 ENC (US5WA45M.000) via GDAL/OGR.
Apply classification rules described in TERRAIN section above.
8. Compute shadow mask for marine platform and ATC tower using radial
elevation-angle march along each azimuth bearing.
9. Write to map/lidar_processed/:
elevation.f32 float32 row-major grid, meters, WGS84
material.u8 uint8 per cell (0=water 1=soil 2=rock 3=concrete)
shadow_marine.u8 uint8 visibility mask for marine radar
shadow_atc.u8 uint8 visibility mask for ATC radar
terrain_meta.json grid dimensions, lat/lon origin, cell size,
source file checksums, processing date
RUNTIME VALIDATION
TerrainMap reads terrain_meta.json at startup and compares the stored
bounding box and cell-size values against current settings.h constants.
If they differ it prints a warning and continues with stale data:
WARNING: terrain data was built with different bounding box or
cell size — re-run terrain_preprocess before exhibit launch.
The exhibit does not crash; it runs with the old grid.
OUTPUT FILES (map/lidar_processed/)
elevation.f32 — float32 elevation grid
material.u8 — uint8 material classification grid
shadow_marine.u8 — uint8 line-of-sight mask, marine radar
shadow_atc.u8 — uint8 line-of-sight mask, ATC radar
terrain_meta.json — metadata and provenance record
These five files are the only terrain inputs at runtime.
The raw zip archives in map/lidar_raw/ are never opened by
the exhibit binary.
==================================================================
FILE LAYOUT (COMPLETE — including additions)
==================================================================
@@ -1082,6 +1315,13 @@ src/
rpi_receiver.h / rpi_receiver.cpp
db_panel.h / db_panel.cpp — Dear ImGui DB management panel
(--database mode only)
terrain_map.h / terrain_map.cpp — DEM load, shadow mask, polar clutter
grid; read-only after init, Thread 1
land_clutter.h / land_clutter.cpp — per-sweep clutter arrays for A-scope
range trace and PPI clutter texture
terrain_preprocess.cpp — standalone offline preprocessing tool;
separate CMake target; links GDAL only;
NOT part of main radar binary
settings.h — all constexpr constants; no .cpp
imgui/ — Dear ImGui source, compiled in
@@ -1091,8 +1331,11 @@ src/
imgui_draw.cpp / imgui_tables.cpp / imgui_widgets.cpp
shaders/
phosphor.vert / phosphor.frag — P1 and P7 via uniforms
phosphor.vert / phosphor.frag — P1 and P7 via uniforms
graticule.vert / graticule.frag
text.vert / text.frag
sweep.vert / sweep.frag
bloom.vert / bloom.frag — FBO bloom post-processing
bloom.vert / bloom.frag — FBO bloom post-processing
terrain_clutter.vert / terrain_clutter.frag — polar clutter texture overlay
on PPI; P7-compatible decay;
bearing offset rotation uniform

202
DESIGN.md
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@@ -402,3 +402,205 @@ No raw `new` or `delete` anywhere in the codebase. No `malloc`/`free`.
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.
17. **Terrain and land clutter** are rendered from pre-processed binary grids
in `map/lidar_processed/`. The offline tool `terrain_preprocess` fuses the
SRTM DEM, both LiDAR surveys, and the S-57 ENC into elevation, material,
and shadow-mask grids. At runtime `TerrainMap` loads these grids once;
`LandClutter` generates a polar clutter texture once per sweep period.
See the TERRAIN CLUTTER VISUAL DESIGN REFERENCE section below for
per-material appearance and speckle tuning guidance.
---
## Terrain Clutter Visual Design Reference
All tunable values described here have corresponding constants in
`src/settings.h`. Edit `settings.h` to change values; this section
explains the perceptual intent behind each constant.
### Purpose
The goal is historical authenticity. Period marine radar operators in the
1950s saw the Bellingham shoreline as a bright, stable ring of returns that
formed a recognizable coastline silhouette. Skilled operators mentally
subtracted this from the display and watched only for moving or changing
returns. That experience should be reproducible on this exhibit.
---
### Material Visual Character
**SOIL** (vegetated land, fields, low hills)
Period appearance: moderate-brightness, moderately grainy returns. The
grain (speckle) is high because vegetation is irregular — individual trees,
bushes, and undulations produce slightly different returns each sweep.
The overall brightness holds steady between sweeps but the texture shimmers.
- σ° constant: `TERRAIN_SIGMA0_SOIL` (~0.010, −20 dB)
- Speckle: `TERRAIN_SPECKLE_SOIL` (suggested starting value: **0.35**)
- Appearance: mid-grey; clearly visible but not dominating. Rolling
hillsides read as a diffuse bright edge along the coastline
and inland ridges.
---
**ROCK** (exposed cliff faces, upper Chuckanut ridgeline, rock outcrops)
Period appearance: brighter than soil, less speckle. Rock faces are
geometrically consistent so returns are stable sweep to sweep. Steep faces
pointing toward the radar return a disproportionately strong echo.
- σ° constant: `TERRAIN_SIGMA0_ROCK` (~0.032, −15 dB)
- Speckle: `TERRAIN_SPECKLE_ROCK` (suggested starting value: **0.20**)
- Appearance: noticeably brighter than soil; Chuckanut Mountain's western
face reads as a bright arc, stable between sweeps. Little
shimmer — the texture is coarser and more consistent.
---
**CONCRETE** (breakwaters, piers, dock structures, Boulevard Park boardwalk,
harbor facilities)
Period appearance: the strongest land returns on the scope after large steel
vessels. Structures built over water (piers on pilings, breakwater walls)
produce corner-reflector effects — the right-angle junction between the
vertical face and the water surface acts as a retroreflector. Operators used
these as navigation aids; the Bellingham harbor entrance is identifiable by
its distinctive bright return pattern.
- σ° constant: `TERRAIN_SIGMA0_CONCRETE` (~0.100, −10 dB)
- Speckle: `TERRAIN_SPECKLE_CONCRETE` (suggested starting value: **0.12**)
- Appearance: bright, stable, low shimmer. Breakwaters and piers appear as
sharp bright lines or arcs. The Boulevard Park boardwalk over
the water appears as a bright thin arc. These features should
be the most prominent land returns on the scope after large
steel ships.
---
**WATER — CALM** (open bay, light wind)
Period appearance: very weak, near-invisible. Calm water reflects most radar
energy away from the antenna (specular reflection). Operators saw a nearly
blank area over open water even at high gain.
- σ° constant: `TERRAIN_SIGMA0_WATER_CALM` (~0.0003, −35 dB)
- Appearance: at normal gain, essentially black. Only visible at extreme
gain settings as a faint salt-and-pepper noise floor.
---
**WATER — ROUGH** (choppy bay, wind >10 knots)
Period appearance: a low-level fuzzy return rising from the noise floor,
affecting the inner ranges most strongly. Sea clutter was a major nuisance
on small-vessel marine radar. The wave clutter filter (keys 5/6) suppresses
this.
- σ° constant: `TERRAIN_SIGMA0_WATER_ROUGH` (~0.010, −20 dB)
- Appearance: at normal gain, a hazy shimmer at short ranges that fades
outward. Heavy speckle — random wave facets scatter
incoherently. The wave clutter filter reduces this.
---
### Speckle / Grain Tuning Guide
Speckle simulates pulse-to-pulse amplitude variation caused by incoherent
scattering from irregular surfaces. Implemented as a per-cell random
fraction multiplied by the computed P_r each sweep:
```
Speckle = P_r × (1.0 + TERRAIN_SPECKLE_xxx × random(−1, +1))
```
Values close to 0.0 give stable, solid returns (correct for concrete and
large flat surfaces). Values closer to 0.5 give vigorous shimmer (correct
for vegetation and choppy water). Values above 0.5 are unrealistically noisy
for terrain — avoid unless simulating a very rough or complex surface.
Suggested starting values:
| Constant | Value | Character |
|-----------------------------|-------|-----------------------------------------|
| `TERRAIN_SPECKLE_SOIL` | 0.35 | visible shimmer, naturalistic |
| `TERRAIN_SPECKLE_ROCK` | 0.20 | moderate, stable with some texture |
| `TERRAIN_SPECKLE_CONCRETE` | 0.12 | mostly stable; slight flicker from edge |
**Tuning procedure:**
1. Set max range to 6 miles on the Marine PPI.
2. Rotate to a bearing showing the Bellingham breakwater and open bay.
3. Adjust `TERRAIN_MARINE_CLUTTER_BRIGHTNESS` until the breakwater return
is clearly bright but does not wash out nearby ship targets.
4. Adjust `TERRAIN_SIGMA0_CONCRETE` if breakwater brightness relative to
soil hills looks wrong.
5. Adjust speckle values until soil hillsides shimmer naturally and concrete
structures hold steady between sweeps.
6. Verify at all three marine range settings (2, 4, 6 miles) that clutter
does not overwhelm vessel targets at any range.
---
### Overall Brightness Balance
The most important perceptual tuning parameter is
`TERRAIN_MARINE_CLUTTER_BRIGHTNESS`. It is a linear scale factor applied to
all terrain return brightness before the clutter texture is uploaded to the
GPU. It does not change the relative balance between materials — it scales
all terrain uniformly.
**Target appearance goal:**
- A steel AIS vessel at 3 miles range should be 2–3× brighter than the
strongest adjacent land clutter return (a concrete breakwater).
- The coastline silhouette should be clearly readable as geography — a
visitor who knows Bellingham Bay should recognize the shape.
- Open water should be visually clean at default gain settings.
Suggested starting value: `TERRAIN_MARINE_CLUTTER_BRIGHTNESS = 0.55`
**ATC PPI:** `ATC_TERRAIN_CLUTTER_SUPPRESSED = true` means land clutter is
hidden by MTI cancellation — no brightness tuning needed for ATC. If
suppression is disabled for debugging, use `TERRAIN_MARINE_CLUTTER_BRIGHTNESS`
as a guide.
---
### Shadow Zones
Shadow zones are the most dramatic visual effect on the Marine PPI. They
appear as dark wedge-shaped gaps in the land clutter pattern, pointing
outward from the radar, behind ridgelines and hills.
Key shadow features visible from the marine bay platform:
- **Chuckanut Mountain** (southwest) casts a prominent shadow into the
southern bay and beyond.
- **Lummi Island** (northwest) shadows a sector of the northern bay.
- **Bellingham waterfront bluff** shadows part of the inner harbor.
These shadows are inherently dark against surrounding clutter — no tuning
required. Shadow = zero amplitude, computed geometrically by the preprocessor.
For the ATC scope with `ATC_TERRAIN_SHADOW_ENABLED = true`, shadows affect
aircraft returns only (not the display background, which is suppressed). An
aircraft descending behind Chuckanut Mountain will fade out and reappear as
it clears the ridge on final approach — authentic behavior of period ASR radar.
---
### Polar Clutter Texture Resolution
`TERRAIN_POLAR_BEARING_BINS` and `TERRAIN_POLAR_RANGE_BINS` control the
resolution of the GPU texture carrying terrain clutter to the shader.
Recommended values:
| Scope | Bearing bins | Range bins | Notes |
|---------------------|-------------|------------|------------------------------|
| Marine PPI (6 mi) | 720 | 512 | 0.5° matches marine beamwidth|
| ATC PPI (20 mi) | 720 | 1024 | wider range needs more bins |
The texture is regenerated once per sweep period (every 4–5 seconds), not
every frame. Upload cost is not time-critical. Reducing to 360 bearing bins
is acceptable and halves the texture upload cost at the expense of slightly
blocky angular transitions near prominent features.

36
additions.lidar
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@@ -0,0 +1,36 @@
I just added the following directories (alrady mentioned in the existing CLAUDE.md file
./map
./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
We need code for the marine a scope and marine ppi scope and the
on-boat ppi radar to show reflectivity from the ./map/charts_enc/US5WA45M.000
and ./map/charts_enc/n48_w123_1arc_v3.tif (include whatever addional shader
files that may be needed. Consider with the topographical map the effect of higher hils
closer to lower hills will shadow the lower hills from the radar where ever the radar is,
which will change if there is a radar on a boat.
The ./map/lidar_raw/wa2016_west_dem_J1364939.zip contains information for the lidar
mapping of any man made structures, including features on the waterfront; breakwaters,
piers, and structures built over the water such as the boulevard park boardwalk
We will need to include the information in the ./map/lidar_raw/wa2016_west_dem_J1364939.zip
file to contribute to the reflection on the shore and land features.
The marine a-scope and the maring PPI scope and the on boat ppi scope needs to show these
features.
The Air traffic control radar in the day would blank out the shore features, but would show
the effects of shadowing of aircraft by the taller hils.
The land featuresl should be subject
to the effects of the radar equation. Consider the materials be soil, rock, and concrete.
In order to provide visual balance, the grain for returns of the shoreline, the mountains and
hills and the man made structures should be included in the settings.h file and DESIGN.md file

116
src/settings.h
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@@ -361,6 +361,122 @@
* range is approximately 2–5)
*/
/*
* ================================================================
* TERRAIN — BOUNDING BOX AND GRID
* ================================================================
* The preprocessor crops both LiDAR surveys to this box and builds
* the binary grids at TERRAIN_PROCESSED_CELL_DEG resolution.
* If any of these values change, re-run terrain_preprocess.
* TerrainMap validates these against terrain_meta.json at startup
* and warns if a mismatch is found.
*
* TERRAIN_BBOX_LAT_MIN Southern edge of processed grid (degrees)
* TERRAIN_BBOX_LAT_MAX Northern edge of processed grid (degrees)
* TERRAIN_BBOX_LON_MIN Western edge of processed grid (degrees)
* TERRAIN_BBOX_LON_MAX Eastern edge of processed grid (degrees)
* Default box covers all three fixed radar locations plus the full
* 20-mile ATC radius: 48.5 N to 49.05 N, 122.0 W to 123.2 W
*
* TERRAIN_PROCESSED_CELL_DEG Cell size in degrees; ~0.0003° ≈ 30 m
* at this latitude. Matches SRTM resolution;
* LiDAR detail is resampled to this grid.
*/
/*
* ================================================================
* TERRAIN — MATERIAL CLASSIFICATION THRESHOLDS
* ================================================================
* Applied by terrain_preprocess during material classification pass.
* Cells above both thresholds are classified as rock; all other
* non-water, non-structure land cells are classified as soil.
*
* TERRAIN_ROCK_THRESHOLD_M Minimum elevation for rock class (meters)
* TERRAIN_ROCK_SLOPE_THRESHOLD_DEG Minimum local slope for rock class (degrees)
* TERRAIN_STRUCTURE_HEIGHT_THRESHOLD_M
* Minimum height above surrounding terrain
* to classify a LiDAR feature as man-made
* concrete (meters; default 2.0)
*/
/*
* ================================================================
* TERRAIN — MATERIAL BACKSCATTER COEFFICIENTS (σ°)
* ================================================================
* Normalized radar backscatter coefficient per material, linear
* (m²/m²). Used in the clutter radar equation inside LandClutter.
* Multiply by cell area and radar equation factors to get P_r.
*
* TERRAIN_SIGMA0_SOIL ~0.010 (−20 dB) moist vegetated land
* TERRAIN_SIGMA0_ROCK ~0.032 (−15 dB) exposed rock, rough face
* TERRAIN_SIGMA0_CONCRETE ~0.100 (−10 dB) hard smooth surface;
* corner reflectors from
* structure edges
* TERRAIN_SIGMA0_WATER_CALM ~0.0003 (−35 dB) flat water, specular
* TERRAIN_SIGMA0_WATER_ROUGH ~0.010 (−20 dB) choppy sea, sea clutter
*/
/*
* ================================================================
* TERRAIN — SPECKLE / GRAIN AMPLITUDES
* ================================================================
* Random amplitude variation applied per cell per sweep to simulate
* the characteristic grainy texture of real radar land clutter.
* Values are fractional (0.0–1.0) multiplied by the computed P_r
* for each cell. See DESIGN.md for perceptual tuning guidance.
*
* TERRAIN_SPECKLE_SOIL Speckle fraction for soil returns
* TERRAIN_SPECKLE_ROCK Speckle fraction for rock returns
* TERRAIN_SPECKLE_CONCRETE Speckle fraction for concrete returns
* (lower than soil — structures are
* geometrically stable, less random)
*/
/*
* ================================================================
* TERRAIN — POLAR CLUTTER GRID DIMENSIONS
* ================================================================
* The polar texture uploaded to the GPU for PPI rendering. Larger
* values give finer angular and range resolution but cost more VRAM
* and upload time. Texture is regenerated once per sweep period.
*
* TERRAIN_POLAR_BEARING_BINS Number of angular bins (360 minimum;
* 720 for 0.5° resolution)
* TERRAIN_POLAR_RANGE_BINS Number of range bins across max range
* (512 is sufficient for 6-mile marine;
* 1024 for 20-mile ATC)
*/
/*
* ================================================================
* TERRAIN — RENDERING AND DISPLAY FLAGS
* ================================================================
*
* TERRAIN_MARINE_CLUTTER_BRIGHTNESS
* Overall brightness scale factor for
* land clutter on marine PPI (0.0–1.0).
* Tuned for visual balance against live
* target returns. See DESIGN.md.
*
* TERRAIN_BOAT_RECOMPUTE_THRESHOLD_DEG
* Reserved for future boat scenario.
* Minimum bearing offset change (degrees)
* before a background shadow recompute
* is triggered when the boat moves.
* Not used in v1 (fixed platforms only).
*
* ATC_TERRAIN_CLUTTER_SUPPRESSED
* true = suppress land clutter on ATC PPI
* (MTI cancellation; default true).
* Set false to show raw land clutter for
* debugging or demonstration purposes.
*
* ATC_TERRAIN_SHADOW_ENABLED true = apply terrain shadow attenuation
* to aircraft returns on ATC PPI.
* Aircraft behind hills appear at reduced
* amplitude or absent (default true).
*/
/*
* ================================================================
* PAR GEOMETRY