1.2-3 Accuracy of Measurements-Measurement of Distances Flashcards
process of determining the extent, size or dimensions of a particular quantity in comparison to a given standard.
measurement
2 types of measurements
direct measurements
indirect measurements
a comparison of the measured quantity with a standard measuring unit or units employed for measuring a quantity of that kind.
Direct Measurements
applying a wire or tape to a line is an example of what type of measurement
Direct Measurements
determining a horizontal or vertical angle with a transit is an example of what type of measurement
Direct Measurements
fitting a protractor between two intersecting lines to
determine the intersection angle is an example of what type of measurement
Direct Measurements
When it is not possible to apply a measuring instrument directly to a quantity to be measured
Indirect Measurements
In this type of measurement, the observed value is
determined by its relationship to some other known
values.
Indirect Measurements
the difference between the true value and the measured value of a quantity
Errors
inherent in all measurements and results from sources which cannot be avoided.
Errors
inaccuracies in measurements which occurred because some aspect of a surveying operation is performed by the surveyor with: carelessness, poor judgment, inattention, and improper execution
Mistakes
are also caused by: misunderstanding the problem, inexperience, and indifference of the surveyor
Mistakes
reading the wrong graduation of the tape is an example of
Mistakes
transposition of figures is an example of
Mistakes
reading a scale backward is an example of
Mistakes
misplacing a decimal point is an example of
Mistakes
incorrect reading of field notes is an example of
Mistakes
2 types of errors
Systematic and Accidental
type of error that will always have the same sign and
magnitude as long as field conditions remain constant and
unchanged.
Systematic Errors
how to eliminate systematic errors (3)
(1) applying corrections
(2) employing proper techniques in the use of instruments
(3) adopting a field procedure which automatically eliminates the error
purely accidental in character caused by factors beyond the control of the surveyor and are present in all surveying measurement
Accidental Errors
The occurrence of such errors are matters of chance as they
are likely to be positive or negative, and may tend in part to
compensate or average out according to ___
laws of probability
due to imperfections in the instruments used, either from faults in their construction or improper adjustments between the different parts prior to their use.
Instrumental Errors
caused by variations in the phenomena of nature such as: temperature, gravity, wind, humidity, curvature of the earth, and refraction changes in magnetic declination
Natural Errors
Sources of errors (3)
Instrumental Errors
Natural Errors
Personal Errors
arise from limitations of the human observer’s senses of sight, touch, and hearing, which are likely erroneous or inaccurate.
Personal Errors
indicates how close a given measurement is to the absolute or true value of the quantity measured.
Accuracy
refers to the degree of refinement and consistency with which any physical measurement is made.
Precision
portrayed by the closeness to one another of a set of repeated measurements of a quantity.
Precision
number of times something will probably occur over the range of possible occurrences.
Probability
the quantity which, based on available data, has more chances of being correct than any other.
MOST PROBABLE VALUE (MPV)
total amount of error in a given measurement should relate to the magnitude of the measured quantity in order to indicate the accuracy of a measurement.
RELATIVE (ERROR) PRECISION
expressed by a fraction having the magnitude of the error in the numerator and the magnitude of a measured quantity in the denominator.
RELATIVE (ERROR) PRECISION
quantity which, when added to and subtracted from the most probable value, defines a range within which there is a 50 percent chance that the true value of the measured quantity lies inside (or outside) the limits thus set.
PROBABLE ERROR
The estimated degree of reliability (or weight) for each of the measurements before they are combined and the most probable values are determined.
WEIGHTED OBSERVATIONS
Methods of Distance Measurement (8)
- Pacing 5. Mathematical
- Taping 6. Mechanical
3.Tachymetric 7. Photogrammetric - Graphical 8. Electronic Distance Measurement
consists of counting the number of steps or paces
in a required distance.
Pacing
A ___ is defined as the length of
step in walking.
pace
To pace a distance, one must first determine the
length of one’s pace. This is referred to as the___.
pace factor
___ is another procedure of obtaining horizontal distances. It is based on the optical geometry of the instruments employed and is an indirect method of measurement.
Tachymetry
A rapid means of determining horizontal distances.
Stadia Method
is a convenient and practical device used for quick and accurate measurement of horizontal distances.
The subtense bar
These methods are widely employed in plane table surveys, and in triangulation works. In inaccessible terrain, this method becomes quite practical to employ.
Distance by Graphical and Mathematical Methods
These devices are only applicable for low-precision surveys or where quick measurements are desired. The more commonly used among these devices include the odometer, measuring wheel, and optical range finder.
Distance by Mechanical Devices
a simple device that can be attached to a wheel for purposes of roughly measuring surface distances.
Odometer
This device can be used to determine distances approximately simply by focusing.
Optical Rangefinder
refers to the measurement of images on a photograph.
Photogrammetry
The tape ___ as the temperature rises and ___ as the temperature falls.
lengthens; shortens
