! Columbus supports keywords that allow you to indicate which coordinate components are
! to be fixed, refraction settings and deflection of the vertical settings. Defined 
! refraction or deflection values apply to all applicable stations and observations that 
! follow in the file. You can turn them off at any time by setting them to zero.




! Example 1: 

! Fixing station components for adjustment. To set station Point Lookout to be fixed in
! 3D, do the following:

! Fix northing coordinate (latitude or north).
_LAT_NORTH_FIX; Point Lookout


! Fix easting coordinate (longitude or east).
_LON_EAST_FIX; Point Lookout


! Fix height coordinate.
_HGT_FIX; Point Lookout




! Example 2:

! Set Refraction correction for Zenith Angle observations that follow in the file.
!              Constant
_REFRACTION;   0.5

! Define some observations with zenith angles.
_OBS_AZ_SET;  A; D; 0.0; 0.001; 93.0; 25.0; 106.25; 0.05; 0; 0
_OBS_HA_SET;  A; B; D; 90.0000; 20.0; 88.0000; 25.0; 93.7500; 0.050; 0; 0
_OBS_ZEN; 101; 102; 93.3030; 15; 0; 0

! Now, turn Zenith Angle constant off or change to another value for zenith observations.
! that follow.
_REFRACTION;  0


! During a 3D adjustment, the actual refraction correction (for each zenith angle) is 
! calculated from the constant using the following equation:

! RC = (K x D) / (2 x R)

! Where:

! RC = refraction correction in radians
! K  = zenith refraction constant (0.0 - 0.5)
! D  = chord (slope distance) between At and TO stations
! R  = radius of earth + ellipsoidal height + instrument height at occupied station

! zenith (corrected) = zenith (uncorrected) + RC




! Example 3:

! Set deflection of the vertical for stations (_STA_COORD records) that follow in the file.
!           Value (in seconds)
_DEFL_NS;   15.0
_DEFL_EW;  -10.0


! Now, turn off
_DEFL_NS;   0
_DEFL_EW;   0


! To set a deflections to zero (where 0.0 is the actual deflection), use a small number.
_DEFL_NS;   0.0001
_DEFL_EW;   0.0001