# Surveying Questions and Answers – Photogrammetric Surveying – Parallax in Aerial Stereoscopic Views

This set of Surveying Objective Questions & Answers focuses on “Photogrammetric Surveying – Parallax in Aerial Stereoscopic Views”.

1. Difference in parallax can be obtained due to___________
a) Distance between zenith
b) Distance between bearing
c) Distance between azimuth
d) Distance between points sights

Explanation: Parallax is a state where there is an apparent movement of point viewed first with one eye and then viewed with another eye. If the difference in distance between the points sighted is measured then it can yield the difference in parallax.

2. Which of the following can be used to view stereo pair?
a) Aerial camera
b) Stereoscope
c) Stereoscopic camera
d) Telescope

Explanation: Stereo pair involves stereoscopic fusion, where the objects which are visualized from left eye and right eye are combined for generating output. Stereo pair can be viewed by using stereoscope and anaglyph.

3. Which of the following doesn’t come under the category of depth perception?
a) Accommodation
c) Divergence
d) Retinal display

Explanation: Depth perception involves determining the relative distance between the objects from the observer. It involves certain clues which are required for photogrammetry. Those are head parallax, convergence, accommodation, retinal display.

4. Which of the following indicates the correct set of stereoscope classifications?
a) Lens and azimuth stereoscope
b) Mirror and azimuth stereoscope
c) Mirror and lens stereoscope
d) Mirror stereoscope and stereo pair

Explanation: Stereo pairs can be interpreted by using stereoscope, which is designed for assisting and magnifying perception of depth. Stereoscope has been classified as mirror stereoscope and lens stereoscope.

5. Which of the following indicate parallax equation for ground co-ordinate point?
a) X = B*x + p
b) X = B*x – p
c) X = B*x * p
d) X = B*x / p

Explanation: The parallax equation for the ground co-ordinates of the point taken into consideration can be given as X = B*x / p. Here, B is the point considered, p is the parallax and x is the numerical value.
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6. The distance between nodal point and plane of photograph depends on datum height.
a) False
b) True

Explanation: The lens of stereoscope is having a greater importance in terms of visualizing an object. Two magnifying lens were used which makes it sight the object in accurate manner. The distance between nodal point and plane of photograph depends on the focal length of the lens.

7. Displacement due to successive exposures can be given as _____________
a) Visual parallax
b) Multiple exposure
c) Exposure
d) Parallax

Explanation: Parallax in case of stereoscopic view can be given as the displacement of point in the image due to successive exposures. In order to minimize the parallax, difference in parallax is calculated. It is the successive difference in the points taken into consideration.

8. The value of overlapping parallax can be determined by ___________
a) P = x / xꞌ
b) P = x – xꞌ
c) P = x * xꞌ
d) P = x + xꞌ

Explanation: The overlapping parallax indicated by symbol p can be determined by the difference of x-coordinate of the point measured on the left hand photograph to the x-coordinate of the point on right hand photograph.

9. Determine the value of parallax, if the x-coordinate on left hand photograph is 54 and on right hand photograph is 32.
a) 24
b) 12
c) 22
d) 27

Explanation: The parallax can be determined by using the formula,
P = x – xꞌ. On substitution, we get
P = 54 – 32
P = 22.

10. Which of the following doesn’t serve as a condition for an aerial stereoscopic view?
a) Excessive overlapping
b) Elevation of camera for exposure
c) Vertical camera axis
d) Sufficient overlapping

Explanation: The conditions for aerial stereoscopic view include photographs with sufficient overlapping, elevation of the camera for exposure and vertical camera axis. These are meant to be ideal conditions.

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