Surveying Questions and Answers – Photogrammetric Surveying – Tilt Distortion or Displacement

This set of Surveying Multiple Choice Questions & Answers (MCQs) focuses on “Photogrammetric Surveying – Tilt Distortion or Displacement”.

1. From the figure, X indicates________

a) Tilted photograph
b) Vertical photograph
c) Oblique photograph
d) Terminated photograph

Explanation: X indicates the tilted photograph. When vertical photograph is placed on a tilted photograph, it can be visualized as shown. This is done to mitigate the errors while correcting the observations taken from the photographs.

2. Determine the tilt displacement if the values of point of rotation and a are 3 and 4m having tilt angle 43˚23ꞌ with focal length 4m.
a) 4.72m
b) 42.72m
c) 24.27m
d) 24.72m

Explanation: The tilt displacement is given as
d = (i*a)2*sin t / f. On substitution, we get
d = (3*4)2*sin 43˚23ꞌ / 4
d = 24.72m.

3. Distance from isocentre is taken into consideration in tilt displacement.
a) False
b) True

Explanation: Tilt displacement or distortion can be defined as the difference of a point in a tilted photograph from isocentre to distance of the same point in a photograph from isocentre. It clearly explains that the distance of the point is measured from isocentre.

4. Relief distortion depends on which of the following?
a) Zenith
b) Flying height
c) Datum
d) Focal length

Explanation: Relief displacement is a point on tilted photograph, which can be placed above nadir point. It depends upon flying height, distance of image from nadir point, elevation from ground and the position of that point from principle line. It can be applied in case of vertical photograph too.

5. The formula for tilt displacement can be given as ___________
a) d = (i+a)2*sin t / f
b) d = (i-a)2*sin t / f
c) d = (i*a)2*sin t / f
d) d = (i*a)2*sin t + f

Explanation: The formula of tilt displacement involves sine of the tilt angle along with focal length of the lens, point of rotation and the displacement point. The entire representation can be done as
d = (i*a)2*sin t / f.

6. The formula of relief displacement can be given as __________
a) d = r*h / H
b) d = r+h / H
c) d = r*h * H
d) d = r-h / H

Explanation: Relief displacement involves the usage of radial distance from nadir point, height from mean sea level, height of the station point. The entire mathematical expression can be described as follows
d = r*h / H.

7. What is the position of relief displacement on vertical photograph?
a) Horizontal
b) Parallel
c) Perpendicular

Explanation: In a vertical photograph, the relief displacement is radial. It is able to connect all the points which are sighted afterwards for better result. In case of tilted photograph, it is not radial.

8. Flying height is used in case of tilted photograph.
a) False
b) True

Explanation: Flying height involves in the placing of a point on the horizon. For placing this nadir point is used as a reference. In general tilted photograph depends on flying height, elevation of the ground point.

9. Tilt displacement of a point on nadir point is _________
a) Half inward
b) Completely outward
c) Half outward
d) Completely inward

Explanation: The tilt displacement of a point on the downward or nadir point is half outward but not full. But in case of the point upward of a half tilted photograph is full inward.

10. Determine the relief displacement if the radial distance is given as 45m with a height from mean sea level and height of the station is given as 2m and 76m respectively.
a) 1.18m
b) 1.81m
c) 9.18m
d) 10.18m

Explanation: The relief displacement can be found out by using the formula,
d = r*h / H. On substitution, we get
d = 45*2 / 76
d = 1.18m.

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