`nx_geo_los.nx` source

1// nx_geo_los.nx -- LIB: GEO-022 LINE-OF-SIGHT / viewshed over a terrain elevation profile (DEM).
2//
3// Given an elevation profile sampled along a transect (heights[0..n]), an observer at index 0 and a
4// target at index n (each with an eye/structure height above ground), the target is VISIBLE iff no
5// intermediate terrain sample rises above the straight sight-line from observer to target.
6//
7// THE EXCEED ANGLE: the sight-line test is INTEGER and cross-multiplied -- compare heights[i]*n
8// against obsH*n + (tgtH-obsH)*i (no division, no float) -> the visible/blocked verdict is EXACT and
9// deterministic, even when a terrain sample sits exactly on the sight-line (decided, not an epsilon
10// coin-flip). Sovereign + offline; the DEM is seeded data, not a service. license_tier: ORIGINAL
11import "nx_syscalls.nx"
12
13// 1 if the target (index n) is visible from the observer (index 0), else 0 (the blocking index can be
14// recovered with geo_los_blocker). obs_eye / tgt_eye are heights ABOVE the ground at each endpoint.
15func geo_line_of_sight(heights: *i64, n: i64, obs_eye: i64, tgt_eye: i64) -> i64 {
16    let obsH: i64 = heights[0] + obs_eye
17    let tgtH: i64 = heights[n] + tgt_eye
18    var i: i64 = 1
19    while i < n {
20        // sight-line height at i = obsH + (tgtH-obsH)*i/n ; compare *n to avoid division.
21        if heights[i] * n > obsH * n + (tgtH - obsH) * i { return 0 }
22        i = i + 1
23    }
24    return 1
25}
26
27// index of the first terrain sample that blocks the sight-line, or -1 if the target is visible.
28func geo_los_blocker(heights: *i64, n: i64, obs_eye: i64, tgt_eye: i64) -> i64 {
29    let obsH: i64 = heights[0] + obs_eye
30    let tgtH: i64 = heights[n] + tgt_eye
31    var i: i64 = 1
32    while i < n {
33        if heights[i] * n > obsH * n + (tgtH - obsH) * i { return i }
34        i = i + 1
35    }
36    return 0 - 1
37}
nx_geo_los.nx source

`nx_geo_los.nx` source
