1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct MoLocation {
/// 0 = North, 1 = South (per spec)
pub north: bool,
/// 0 = East, 1 = West (per spec)
pub east: bool,
/// 0..=90
pub lat_deg: u8,
/// 0..=59_999 (thousandths of a minute)
pub lat_thousandths_min: u16,
/// 0..=180
pub lon_deg: u8,
/// 0..=59_999 (thousandths of a minute)
pub lon_thousandths_min: u16,
/// Circular Error Probable radius in kilometers (80% probability).
pub cep_km: u32,
}
#[derive(Clone, Copy, Debug)]
pub enum MoLocationError {
ReservedBitsNonZero(u8),
LatDegOutOfRange(u8),
LatThousandthsOutOfRange(u16),
LonDegOutOfRange(u8),
LonThousandthsOutOfRange(u16),
}
impl MoLocation {
/// Parse the 11-byte MO Location IE value into fields.
///
/// Layout (11 bytes total):
/// b0: NSI/EWI flags + reserved/format (reserved should be 0)
/// b1: latitude degrees (0..=90)
/// b2: latitude thousandths-of-minute (MSB)
/// b3: latitude thousandths-of-minute (LSB)
/// b4: longitude degrees (0..=180)
/// b5: longitude thousandths-of-minute (MSB)
/// b6: longitude thousandths-of-minute (LSB)
/// b7..b10: CEP radius (u32, km), big-endian
///
/// NSI: 0=North, 1=South; EWI: 0=East, 1=West.
pub fn parse(bytes: [u8; 11]) -> Result<Self, MoLocationError> {
let b0 = bytes[0];
// Per spec, reserved/format code bits should be 0.
// Only the two lowest bits (we use bit0/bit1) are meaningful (NSI/EWI).
let reserved = b0 & !0b0000_0011;
if reserved != 0 {
// Non-fatal spec violation in the field — up to you whether to hard error or just warn.
return Err(MoLocationError::ReservedBitsNonZero(b0));
}
// Choose bit 1 for NSI and bit 0 for EWI.
// Spec states 0=North,1=South and 0=East,1=West respectively.
let north = (b0 & 0b0000_0010) == 0;
let east = (b0 & 0b0000_0001) == 0;
let lat_deg = bytes[1];
if lat_deg > 90 {
return Err(MoLocationError::LatDegOutOfRange(lat_deg));
}
let lat_thousandths_min = u16::from_be_bytes([bytes[2], bytes[3]]);
if lat_thousandths_min > 59_999 {
return Err(MoLocationError::LatThousandthsOutOfRange(
lat_thousandths_min,
));
}
let lon_deg = bytes[4];
if lon_deg > 180 {
return Err(MoLocationError::LonDegOutOfRange(lon_deg));
}
let lon_thousandths_min = u16::from_be_bytes([bytes[5], bytes[6]]);
if lon_thousandths_min > 59_999 {
return Err(MoLocationError::LonThousandthsOutOfRange(
lon_thousandths_min,
));
}
let cep_km = u32::from_be_bytes([bytes[7], bytes[8], bytes[9], bytes[10]]);
Ok(MoLocation {
north,
east,
lat_deg,
lat_thousandths_min,
lon_deg,
lon_thousandths_min,
cep_km,
})
}
/// Decimal degrees, positive north, negative south.
pub fn latitude_deg(&self) -> f64 {
let minutes = self.lat_thousandths_min as f64 / 1000.0;
let dd = self.lat_deg as f64 + minutes / 60.0;
if self.north {
dd
} else {
-dd
}
}
/// Decimal degrees, positive east, negative west.
pub fn longitude_deg(&self) -> f64 {
let minutes = self.lon_thousandths_min as f64 / 1000.0;
let dd = self.lon_deg as f64 + minutes / 60.0;
if self.east {
dd
} else {
-dd
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_parse_mo_location() {
// flags=01 (north, west), 37° 30.000' N, 122° 15.000' W, CEP=5 km
// thousandths-of-minute: 30.000' -> 30000 (0x7530), 15.000' -> 15000 (0x3A98)
let bytes: [u8; 11] = [
0x01, 0x25, 0x75, 0x30, 0x7A, 0x3A, 0x98, 0x00, 0x00, 0x00, 0x05,
];
let loc = MoLocation::parse(bytes).unwrap();
assert!(loc.north && !loc.east);
assert_eq!(loc.lat_deg, 37);
assert_eq!(loc.lat_thousandths_min, 30_000);
assert_eq!(loc.lon_deg, 122);
assert_eq!(loc.lon_thousandths_min, 15_000);
assert_eq!(loc.cep_km, 5);
let lat = loc.latitude_deg();
let lon = loc.longitude_deg();
assert!((lat - 37.5).abs() < 1e-9);
assert!((lon + 122.25).abs() < 1e-9);
}
}