I think Therion subtract the magnetic declination before to transfer
data Survex. Now to compare better I have put magnetic declination to 0.
declination 0.00 degrees
Data transferred to Survex by the "data.svx" file
*data normal from to tape compass clino
1 2 0.000000 269.423853 0.000000
1 3 2.330000 236.223853 -11.400000
3 4 4.510000 162.623853 -32.200000
4 5 12.410000 0.923853 -77.700000
5 6 1.950000 212.073853 -17.150000
You can see Therion do a wrong fore/back sight compass average
calculation. The good data average are:
1 3 236.8 -11.4
3 4 163.2 -32
4 5 1.5 -77.7
5 6 212.65 -17.15
I think the problem is the average calculation formula in "thdb1d.cxx"
// check backwards compass reading
if ((lei->data_type == TT_DATATYPE_NORMAL) ||
(lei->data_type == TT_DATATYPE_DIVING) ||
(lei->data_type == TT_DATATYPE_CYLPOLAR)) {
if (!thisnan(lei->backbearing)) {
if (thisnan(lei->bearing)) {
lei->backbearing -= 180.0;
if (lei->backbearing < 0)
lei->backbearing += 360.0;
lei->bearing = lei->backbearing;
}
else {
lei->backbearing -= 180.0;
if (lei->backbearing < 0)
lei->backbearing += 360.0;
// calculate average of two angles
//lei->bearing += lei->backbearing;
//lei->bearing = lei->bearing / 2.0;
double sumx, sumy;
sumx = cos((90.0 -
lei->bearing)/180.0*THPI) + cos((90.0 - lei->backbearing)/180.0*THPI);
sumy = sin((90.0 -
lei->bearing)/180.0*THPI) + sin((90.0 - lei->backbearing)/180.0*THPI);
lei->bearing = 90.0 - (atan2(sumy,
sumx) / THPI * 180.0);
if (lei->bearing < 0.0)
lei->bearing += 360.0;
}
}
}
I think the formula is too complicated. I purpose a simpler formula, like:
If bearing <=180
AverageBearing = (bearing + (backbearing -180))/2
else
AverageBearing = (bearing + (backbearing +180))/2
Regards,
Evaristo.
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