Backsight Types and Tolerances

TYPEAB / TYPEVB = Corrected / Normal [,<degree tolerance>] [,X]

The azimuth and vertical angle fields on compass and tape (CT) data lines can optionally contain backsight versions of the measurements.  During processing, the FS/BS values are simply averaged after the appropriate units conversions and instrument corrections are applied.  For example, you could have vectors defined as follows:

...

S1        S2        30        100/282                /-16  ;no forward inclination

S2        S3        15.5        355/181                6/-5

With the program's defaults in effect -- that is, with "TYPEAB=N,5" and "TYPEVB=N,5" -- the program will detect a FS/BS mismatch.  That's because the difference between 355 and the reverse of 181 is more than 5 , the default tolerance in degrees.

Since apparently some cave surveyors prefer to record "corrected" backsights, the program also allows you to define the same vectors as follows:

...

#Units TypeAB=C,6 TypeVB=C

S1        S2        30        100/102                /16

S2        S3        15.5        355/1                6/5

This changes the backsight type of both azimuths and inclinations from Normal to Corrected, and increases the AB tolerance to six degrees so that the second vector passes the test.

Update: Another option in the handling of backsights is to to use them only as a check against blunders. If a trailing ",X" is present in the arguments for TYPEAB or TYPEVB then no averaging will occur; the foresight alone will be used in determining the vector's orientation. Use of this option requires that the other arguments be present also, such as in TypeAB=N,5,X.

Whether or not averaging is suppressed, FS/BS mismatches are treated as non-fatal errors during the compilation of raw data. The program generates a log of such errors (if any exist) and prompts you to inspect it in an editor window when compilation is complete. The first item on each line is a hot link to the appropriate survey file and line. A toolbar button, with the image of a clipboard marked with a red "E", allows you to open the error log for an item's most recent compilation.