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Reject out-of-range latitudes when doing CPR decoding.

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If a CPR message with an undetected error is received this can produce out-of-range results for latitude.
e.g. even latitude of 78000, odd latitude of 0 produces a latitude index j=35 and rlat0 = 213.
This commit is contained in:
Oliver Jowett 2014-09-25 15:49:39 +01:00
parent a82df07c0c
commit e5b3572e8b
1 changed files with 9 additions and 0 deletions
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9
mode_s.c
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@ -2053,6 +2053,9 @@ void decodeCPR(struct aircraft *a, int fflag, int surface) {
if (rlat1 >= 270) rlat1 -= 360;
}
// Check to see that the latitude is in range: -90 .. +90
if (rlat0 < -90 || rlat0 > 90 || rlat1 < -90 || rlat1 > 90) return;
// Check that both are in the same latitude zone, or abort.
if (cprNLFunction(rlat0) != cprNLFunction(rlat1)) return;
@ -2129,6 +2132,12 @@ int decodeCPRrelative(struct aircraft *a, int fflag, int surface) {
rlat = AirDlat * (j + lat/131072);
if (rlat >= 270) rlat -= 360;
// Check to see that the latitude is in range: -90 .. +90
if (rlat < -90 || rlat > 90) {
a->bFlags &= ~MODES_ACFLAGS_LATLON_REL_OK; // This will cause a quick exit next time if no global has been done
return (-1); // Time to give up - Latitude error
}
// Check to see that answer is reasonable - ie no more than 1/2 cell away
if (fabs(rlat - a->lat) > (AirDlat/2)) {
a->bFlags &= ~MODES_ACFLAGS_LATLON_REL_OK; // This will cause a quick exit next time if no global has been done