FEMA US&R Response Sys/U.S. Army Corps of Engineers
STRUCTURES SPECIALIST SKILLS TRAINING October 2007
TST – Total Station Training
Distance Measurement
PT- A
PT- B
HD
HI SD
HT
VD
Instrument
Constant
Prism
Constant
P
Prism
MD
HI = the height of the instrument (vertical distance from station point at Point A
to axis of telescope).
HT = the height of the target (vertical distance from measured point at Point B to
the prism).
MD = the distance measured by the EDM (measured distance from the total
station axis to the prism focus).
SD = the slope distance (computed distance along the inclined line from the
station point to the measured point).
= the angle of the instrument relative to horizontal (90
o
- Zenith Angle).
HD = the horizontal distance from the station point to the measured point.
VD = the vertical distance from the station point to the measured point.
PC = the prism constant, obtained from the manufacturer of the prism, usually
etched on the prism frame. Prisms have different constants (PC):
• Large prism = 30 mm (Not part of cache)
• Mini prism = 18mm
• Reflector sheet = 0 mm
• Prism-less = 0 mm
Instrument Constant = Property of the instrument set at the factory.
Measurement Basics and Theodolite Use Page 3
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