FUNDAMENTAL SURVEYING Surveying Equipment and Technology 2 — Questions and Answers
Question 1: What is 'photogrammetry' in the context of surveying?
- The science of measuring distances with a camera flash
- The science of deriving reliable measurements and 3D models from photographs (Correct answer)
- The use of satellites for position determination
- A method of sonar-based underwater surveying
Correct answer: The science of deriving reliable measurements and 3D models from photographs
Photogrammetry extracts metric measurements, elevations, and 3D models from overlapping photographs using principles of geometry.
Question 2: What is the main purpose of ground control points (GCPs) in drone photogrammetry?
- To provide landing zones for the drone
- To georeference the photogrammetric model to a known coordinate system with accurate ground coordinates (Correct answer)
- To calibrate the camera's focal length
- To block obstructions in the flight path
Correct answer: To georeference the photogrammetric model to a known coordinate system with accurate ground coordinates
GCPs are surveyed points with known coordinates placed in the project area to georeference and improve the accuracy of the photogrammetric model.
Question 3: What is the difference between absolute accuracy and relative accuracy in surveying?
- Absolute accuracy is always higher than relative accuracy
- Absolute accuracy describes position accuracy relative to a datum; relative accuracy describes position accuracy between points in the survey (Correct answer)
- Relative accuracy uses GPS; absolute accuracy uses total stations
- They are the same concept
Correct answer: Absolute accuracy describes position accuracy relative to a datum; relative accuracy describes position accuracy between points in the survey
Absolute accuracy measures how close a position is to its true location on the datum, while relative accuracy measures how precisely positions relate to each other within the survey.
Question 4: What is 'ground sampling distance' (GSD) in drone photogrammetry?
- The horizontal distance between drone flight lines
- The size of one pixel on the ground in a drone image (Correct answer)
- The depth of penetration of LiDAR pulses
- The distance between GCPs
Correct answer: The size of one pixel on the ground in a drone image
GSD is the real-world distance represented by a single pixel in a drone image, determining the spatial resolution of the final orthophoto and DEM.
Question 5: What is the purpose of a 'prism constant' applied to total station measurements?
- To correct for atmospheric refraction
- To compensate for the physical offset between the prism center and the reflecting face (Correct answer)
- To account for instrument tilts
- To correct for Earth curvature
Correct answer: To compensate for the physical offset between the prism center and the reflecting face
The prism constant corrects for the physical distance between the reflective face of the prism and its center (pole mounting point), ensuring measured distances are to the ground point.
Question 6: Which GNSS constellation is operated by the United States government?
- GLONASS
- Galileo
- GPS (NAVSTAR) (Correct answer)
- BeiDou
Correct answer: GPS (NAVSTAR)
GPS (Global Positioning System / NAVSTAR) is operated by the US Department of Defense, one of four major global satellite navigation systems.
FUNDAMENTAL SURVEYING Surveying Equipment and Technology 2
What is 'photogrammetry' in the context of surveying?