What is TOTAL SURVEY ERROR? What does TOTAL SURVEY ERROR mean? TOTAL SURVEY ERROR meaning

ERRORS IN SURVEYING

* Accuracy is defined as correctness/degree of perfection in reaching an intended target.

* Precision is the degree of perfection used in instruments and the method of observations and

calculations.

* Types of errors creeping in surveying are:

1. Mistakes

2. Systematic/cumulative errors

3. Accidental/compensating errors

* The sources of errors are:

1. Instrumental 2. Natural

3. Human limitations 4. Carelessness

* Though accidental errors are unpredictable, the following features are found:

1. Positive and negative errors will occur with equal frequency

2. Small errors occur more frequently

3. Very large errors do not occur

* Principles of least square is applicable to normal distribution.

1. Standard deviation s = ±

2. Probable error of single observation

= ± 0.6745

3. Most probable error of mean

= ± 0.6745

4. Maximum error = ± 3.29 s

where n = the number of observations

v = difference between any single observation and the mean

* If the relationship between computed and measured quantity is known, error propagation can be

calculated. If y is computed quantity, x is measured quantity and y = f(x),

dy =

* The permissible errors are:

1. Measurements with chain on rough ground : 1 in 250

2. Measurements with chain on average condition: 1 in 500

3. Measurements with steel tape : 1 in 1000

4. Base line measurement : 1 in 10,000

* Relative accuracy between linear and angular measurements

H = L cos q

dH = –L sin q dq

= dq = tan q dq, if sign is ignored

\ dq =

= seconds

Measurements of Horizontal Distance with Chain and Tape

* Methods of measurements:

1. Approximate – pacing

– with passometer

– with pedometer

– with odometer

– with speedometer

2. Chain and tape – Gunter’s or surveyor’s chain

– Revenue chains

– Engineer’s chains

– Metric chain

– Steel bond

– Cloth or linen tape

– Metallic tape

– Steel tape

– Invar tape

* Accessories required are: arrows, pegs, ranging rods, ranging poles, offset rods, laths, whites,

plumb hob and line ranger.

* For ranging a survey line direct method is used. If the two stations are not mutually visible go for

reciprocal ranging.

* In surveying all distances measured should be horizontal. If ground is sloping method of stepping or

any indirect method may be employed. For base line measurement a wire with spring balance,

intermittent stakes and straining poles are used.

* Corrections for absolute length, slope, temperature, pull and sag are made for accurate

measurements.

* If A is the measured area with incorrect tape, the corrected area A¢ is given by

A¢ = = if c is small

where L¢ is corrected length

and l is designated length

c is correction per chain length

* Correction for slope

Csl = L (1 – cos q)

* Correction for temperature

Ct = L µ (Tm – To

)

* Correction for pull

Cp =

* Correction for sag

Cs =

where W = weight of tape per span length

P = pull applied

L = measured length

Chain Surveying