When correcting a traverse for curvature and refraction, TPC applies the curvature and refraction correction to each control point following the Initial point up to and including the Closing point. The Initial point itself is not affected by this correction. Side shots are also adjusted. TPC even applies C&R to benchmark observations in order to compute a more accurate height of instrument equivalent.
TPC uses the following equations to adjust for C&R:
HD = (SD*SIN(ZA)) - [(1-(0.5*COEF)) / RADIUS * (SD*COS(ZA)) * (SD*SIN(ZA))]
VD = (SD*COS(ZA)) + [(1-COEF) / (2*RADIUS) * (SD*SIN(ZA)) * (SD*SIN(ZA))]
HD= computed horizontal distance
VD= computed vertical distance
SD= measured slope distance
ZA= measured zenith angle
COEF= 0.13 = est. coefficient of refraction
RADIUS= 20,906,000 ft or 6,372,200 m
= estimated radius of the earth
Although these equations do not incorporate height of instrument in the radius, they give very good estimates under typical conditions.
TPC will not apply this adjustment if raw data does not exist.
Applying Curvature and Refraction
Applying a Scale Factor
Adjusting a Traverse