func DecodeCompressedPositionReport(c string) (geospatial.Point, rune, rune, string, error) {
// Example: =/5L!!<*e7OS]S
var err error
var matches []string
p := geospatial.Point{}
pr := regexp.MustCompile(`[=!]([\\\/])(.{4})(.{4})(.)(..)(.)(.*)$`)
remains := pr.ReplaceAllString(c, "")
p.Time = time.Now()
if matches = pr.FindStringSubmatch(c); len(matches) > 0 {
if len(matches[7]) > 0 {
remains = matches[7]
}
symTable := rune(matches[1][0])
symCode := rune(matches[4][0])
p.Lat, err = DecodeBase91Lat([]byte(matches[2]))
if err != nil {
return p, ' ', ' ', remains, fmt.Errorf("Could not decode compressed latitude: %v\n", err)
}
p.Lon, err = DecodeBase91Lon([]byte(matches[3]))
if err != nil {
return p, ' ', ' ', remains, fmt.Errorf("Could not decode compressed longitude: %v\n", err)
}
// A space in this position indicates that the report includes no altitude, speed/course, or radio range.
if matches[5][0] != ' ' {
// First we look at the Compression Byte ("T" in the spec) and check for a GGA NMEA source.
// If the GGA bits are set, we decode an altitude reading. Otherwise, try to decode a course/
// speed reading or a radio range reading
if (byte(matches[6][0])-33)&0x18 == 0x10 {
// This report has an encoded altitude reading
p.Altitude, err = DecodeBase91Altitude([]byte(matches[5]))
if err != nil {
return p, ' ', ' ', remains, fmt.Errorf("Could not decode compressed altitude: %v\n", err)
}
} else if (byte(matches[5][0])-33) >= 0 && (byte(matches[5][0])-33) <= 89 {
p.Heading, p.Speed, err = DecodeBase91CourseSpeed([]byte(matches[5]))
} else if matches[5][0] == '{' {
p.RadioRange = DecodeBase91RadioRange(byte(matches[5][1]))
}
}
return p, symTable, symCode, remains, nil
}
return p, ' ', ' ', remains, nil
}
