TACHYMETRYLESSON 5LESSON 5

Variable angleVariable angle

Substence Substence system system

SUBSTENCE SYSTEMSUBSTENCE SYSTEMHorizontal staffHorizontal staff

The substance system is a particular form of the tangential system where the measured base is measured base is held horizontallyheld horizontally

The substance bar is a specially made instrument supported on a tripod with two supported on a tripod with two sighting targets set sighting targets set a precise distance apart, usually 2m.

The central target in the substance bar is placed midway between the end targets for traverse midway between the end targets for traverse angle measurementangle measurement and for use in sighting with the auxiliary base method.

Work procedureWork procedure

Formula For Substence Formula For Substence SystemSystem

2cot2

sH 2

cot2

sH 2

cot2

sH 2

cot2

sH

2cotH

.

2cot2

sH 2

cot2

sH

horizontal distance horizontal distance

2cot2

sH 2

cot2

sH

2cot2

sH

Usually the bar is 2m long to simplify the Usually the bar is 2m long to simplify the calculationcalculation

2cotH

V = H tan θ dH = hi ±V – hb

where dH = difference of height hi = Height of the theodolite V = vertical component Hb = Height of substance bar

So, the reduced level of the staff position Y, RL y = RL X + dHXY

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