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What is adjustment computations?

Estimation of errors in measured quantities

Distribute the errors (random) in the measured quantitiesto make them more accurate and consistent with thegeometric condition for the quantities

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- survey observations- accuracy and precision- redundant observations- adjustment

Survey observations

a way or process of determining the value of an unknown

quantity

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Those are instruments and methods for

the measurement, collection andmanagement of Earths spatial data in

surveying science and geomatics

Measured or observed dataalways contain errors and they must be

processed before be utilized forsurveying and mapping purposes

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Accurate or Precise shots?

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Survey observations

a way or process of determining the value of an unknown quantity

Errors

.are the differences between observed or measured or derived values and

standard or true values of the quantity of interest

Survey observations contain errors that can be categorized as

- gross error

- systematic error or bias

- random error

Gross and systematic errors can be removed from the observations

Random errors cannot be eliminated but can be controlled

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Random errors

- due top human and instruments imperfection

- small magnitude and can be positive or negative

- dealt based on law of probability or statistics

Error effects

- repeated observations of same quantity, same condition give different values- small difference between repeated observations indicates small error and theobservation is precise

- precision and accuracy are two different things. Explain.

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Detection the presence of random errors

- comparison between observations and certain conditions that fit to thegeometry of the measurements

- Examples:> total elevation difference in a closed loop is zero

> total internal angles of a triangle is 180 deg

> total angles around the horizon at a point is 360 deg

> total latitude and departure of a closed traverse is zero

- the conditions involve more than one observation, i.e. redundantobservations

- redundant observations are observations that exceed the minimumnumber needed to determine the unknown. Give examples.

- redundant observations allow the detection of random error and adjustmentbe made to get a final or most probable value for the unknown.

- What is the difference between adjustment and correction of observations?

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Redundant observations

Example: Observation of three angles of a plane triangle (say A, B and C)

Number of redundant observation is ONE

If only angles A and B were observed, the angle C could be computed as

C = 180 A B. Hence, C is unnecessary. If C is observed, it is a redundant.

Advantage of value C from observation:

Enable to assess error and to decide whether to accept or reject theobservation

To make possible adjustment to the observed values in order to derivehigher precision values or Most Probable Values (MPV) for the unknownquantity.