Geomatics Engineering

 👉Actual Distance = (Measured Distance/Nominal length of chain) x Actual length of chain

👉Offsets are lateral measurements made w.r.t main survey line which may be oblique or perpendicular in nature.

👉In aerial photogrametery the photographs are taken at proper interval to provide generally 60% longitudinal overlap and 30 % side overlap.

👉The tape corrections used in Surveying

• Correction for Standardization (+ or -)
• Correction for Slope (Always negative)
• Correction of Pull (+ or -)
• Correction for Temperature (+ or -)
• Correction for Sag (Always negative)
• Normal Tension 
• Correction for Misalignment (Always negative)

👉 Tape correction for standardization (Csd):

                            Csd = (l'-l)/l x L

where, l = nominal length of tape
          l’ = actual length of tape

          L = measured length

          Csd = Correction for standardization

 👉 Correction for Slope (Cs):

        

Where,

                    D = horizontal equivalent
                    L = slope distance
            

                        

     Where,          h = difference in elevations of the end points

                           Cs = correction due to slope

 

👉 Correction for Pull (Cp):

The correction of pull is computed as

Where,
P = pull applied during measurement.
Po = Standard pull
L = Measured length
A = Cross- sectional area of the tape
E = Young’s modulus of material of tape

👉Correction for Temperature (Ct):

The correction for temperature is computed as

Ct = α (Tm - To) L

where,
α = coefficient of linear expansion
Tm = Mean temperature of the tape
To  = Standard temperature

👉 Sag Correction (Csg):

• A tape is supported at two ends, it takes the shape of a CATENARY. 
• The correction for sag should be applied as the horizontal chord Length is always shorter than the curved length

Where,
W = Weight of tape per unit length.
P = Applied pull.
l1 = length of the tape suspended between the supports.

The above equation can also be written in the form of total weight of tape

where,
W = total weight of tape between the supports

👉 Normal Tension:

The normal tension is a tension at which the effects of pull and sag are neutralized.

     

👉Correction for Misalignment (Cm):

•  If L1 = L2 then Cm = d² / L (Negative)

👉Optical square is used to establish two points at right angle. The principle used is double reflection.

👉Method commonly used in Reconnaissance surveying for measurement of horizontal distance are PACING, PASSOMETER, PEDOMETER, ODOMETER,MEASURING WHEEL, SPEEDOMETER,PERAMBULATOR.

👉Equation of cubic parabola  = X^3/6RL

👉Shift in Transition Curve = L^2/24R