Engineering Survey I
Basic Surveying Techniques
3
Corrections to Linear Measurement and their Application:-
Tape Corrections
The corrections performed for seven common errors in linear measurements by tape are:
→ Correction for absolute length →Correction for Slope
→ Correction for pull or tension → Correction for Alignment
→ Correction for temperature → Reduction for the sea level
→ Correction for Sag
Absolute length correction
If Ca is the correction for absolute length or the actual length, then it is
given by:
• Ca = Lc/l
• Where, L = Measured length of the line; c = Correction per tape length;
l= designated length of the tape or the nominal length.
• Different cases are:
• Absolute length > Designated length means Measured distance is
short, hence the correction is additive.
• Absolute length < Designated length means, Measured distance is
long, hence the correction is subtractive.
• The sign of correction Ca is the same as that of 'c'.
α
α
• A 30-m steel tape standardized at 20°C and supported throughout
under a tension of 5.45kg was found to be 30.012m long. The tape had
a cross-sectional area of 0.050 cm² and a weight of 0.03967 kg/m. This
tape was held horizontal, supported at the ends only, with a constant
tension of 9.09 kg, to measure a line from A to B in three segments. The
data listed in the following table were recorded. Apply corrections for
tape length, temperature, and sag to determine the correct length of
the line.
Solution:
(a) The tape length correction is: C L=[30.0 + 30.0 + 21.151] [30.012 -30.00]/30.00 = +0.0324 m
Triangulation
Traversing
PLANE TABLE SURVEYING
BCE ab...080 40
PLANE TABLE SURVEYING
• Plane table survey is mainly suitable for filling interior details when
traversing is done by theodolite
• sometimes traversing by plane table may also be done.
• But this survey is recommended for the work where great accuracy is
not required.
• As the fitting and fixing arrangement of this instrument is not perfect,
most accurate work cannot be expected.
PLANE TABLE SURVEYING
• Accessories of Plane Table :-
BCE ab...080 48
Assignment
