Use lat Lon instead of regions to control messaging distance

[mikecarper]

regions take a lot of effort and coordination. A distance from first hop metric might make more sense. Most repeaters have their location set; use that information for controlling how far a packet will travel. Doesn't require any special configuration and is somewhat easy to understand if you're looking at a map.

Start at 20km and have the final be unlimited

[446564]

Or even a geofence 😎 but much harder to do

[mikecarper]

Needs 4 bytes to include the lat long of the first repeater it hits

#define DEG2RAD_F (0.01745329251994329577f)
#define EARTH_R_M (6371000.0f)

static inline float radf(float deg) { return deg * DEG2RAD_F; }

/* Returns true if distance(lat1,lon1 -> lat2,lon2) <= max_km (approx). */
static bool within_km_fast(float lat1_deg, float lon1_deg,
                           float lat2_deg, float lon2_deg,
                           float max_km)
{
    float lat1 = radf(lat1_deg);
    float lon1 = radf(lon1_deg);
    float lat2 = radf(lat2_deg);
    float lon2 = radf(lon2_deg);

    float dlat = lat2 - lat1;
    float dlon = lon2 - lon1;

    float x = dlon * cosf(0.5f * (lat1 + lat2));
    float y = dlat;

    float s2 = x*x + y*y;  /* approx (distance/R)^2 */

    float max_m = max_km * 1000.0f;
    float t = max_m / EARTH_R_M;
    float t2 = t * t;

    return s2 <= t2;
}

Something like this