Certified Photogrammetrist Camera Calibration & Sensor Geometry 1 — Questions and Answers
Question 1: What is the principal point in camera calibration?
- The point where the optical axis intersects the image plane (Correct answer)
- The geometric center of the image frame
- The midpoint between two fiducial marks
- The projection center of the lens
Correct answer: The point where the optical axis intersects the image plane
The principal point is where the optical axis intersects the image plane, representing the foot of the perpendicular from the perspective center to the image plane.
Question 2: Which distortion model parameter primarily describes symmetric radial lens distortion?
- Affinity coefficient
- K1 radial distortion coefficient (Correct answer)
- Decentering coefficient P1
- Principal point offset
Correct answer: K1 radial distortion coefficient
K1 is the primary radial distortion coefficient that describes symmetric, rotationally symmetric distortion measured from the lens center outward.
Question 3: What does interior orientation define in photogrammetry?
- The position and attitude of the camera in the world coordinate system
- The geometric relationship between the image plane and the perspective center (Correct answer)
- The spatial relationship between overlapping images
- The transformation from pixel to ground coordinates
Correct answer: The geometric relationship between the image plane and the perspective center
Interior orientation defines the geometric relationship between the image coordinate system and the perspective center, including focal length, principal point location, and lens distortion parameters.
Question 4: In aerial photography, fiducial marks are used primarily to:
- Measure ground control points
- Define the image coordinate system (Correct answer)
- Calibrate the onboard GPS receiver
- Determine the aircraft flight altitude
Correct answer: Define the image coordinate system
Fiducial marks are reference points etched into the camera's focal plane that define the image coordinate system and allow transformation from scanner to image coordinates.
Question 5: What is the calibrated focal length (CFL) in photogrammetry?
- The manufacturer's nominal specified focal length
- The distance from the rear nodal point to the film plane
- The focal length value that minimizes the overall effect of radial distortion across the image (Correct answer)
- The focal length measured when focused at infinity
Correct answer: The focal length value that minimizes the overall effect of radial distortion across the image
The calibrated focal length is the value that minimizes the overall effect of radial lens distortion across the image format, and may differ slightly from the manufacturer's specification.
Question 6: Which laboratory calibration method uses precision optical collimators to simulate distant targets at infinity?
- Test field calibration
- Stellar calibration
- Goniometer calibration (Correct answer)
- On-the-job self-calibration
Correct answer: Goniometer calibration
Goniometer calibration uses a precision instrument with collimators to project parallel rays simulating targets at infinity, enabling measurement of angular relationships and lens distortion in a controlled lab environment.
Question 7: The image scale (s) of a vertical aerial photograph with focal length f taken at flying height H above datum is expressed as:
- s = f / H (Correct answer)
- s = H / f
- s = f × H
- s = f + H
Correct answer: s = f / H
Image scale equals focal length divided by flying height above datum (s = f/H); a longer focal length or lower flying height produces a larger (more detailed) scale.
Certified Photogrammetrist Camera Calibration & Sensor Geometry 1
What is the principal point in camera calibration?