Camera Calibration & Sensor Geometry Flashcards

What is the principal point in camera calibration?

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.

Which distortion model parameter primarily describes symmetric radial lens distortion?

Answer: K1 radial distortion coefficient

K1 is the primary radial distortion coefficient that describes symmetric, rotationally symmetric distortion measured from the lens center outward.

What does interior orientation define in photogrammetry?

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.

In aerial photography, fiducial marks are used primarily to:

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.

What is the calibrated focal length (CFL) in photogrammetry?

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.

Which laboratory calibration method uses precision optical collimators to simulate distant targets at infinity?

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.

The image scale (s) of a vertical aerial photograph with focal length f taken at flying height H above datum is expressed as:

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.

What causes decentering (tangential) lens distortion?

Answer: Misalignment of optical elements from the optical axis within the lens system

Decentering distortion is caused by the physical misalignment or decentering of lens elements from the optical axis, producing an asymmetric distortion pattern.

What is the purpose of a reseau grid (reseau plate) in analog aerial cameras?

Answer: To provide reference marks for detecting and correcting film deformation

A reseau grid contains precisely positioned crosses or dots imaged onto the film, allowing detection and correction of film deformation that may occur during processing or scanning.

In digital aerial cameras, what component replaces the photographic film at the focal plane?

Answer: The CCD or CMOS image sensor

In digital cameras, the CCD or CMOS sensor array is positioned at the focal plane to capture light, directly replacing the role of photographic film as the image recording medium.

In digital photogrammetry, pixel size of the sensor is most directly related to:

Answer: The ground sample distance (GSD)

Pixel size directly determines the ground sample distance (GSD) for a given flying height and focal length; GSD defines the smallest ground detail that can be resolved.

Which camera calibration parameter corrects for non-orthogonality (shear) between the x and y axes of the image coordinate system?

Answer: Affinity (shear) parameter

The affinity or shear parameter corrects for non-orthogonality between the image coordinate axes, which can result from imperfect sensor geometry or digitizer scanning.

The Modulation Transfer Function (MTF) in optical and sensor systems is used to measure:

Answer: The ability of the system to resolve and transfer spatial frequency detail

MTF quantifies how well an optical system transfers contrast from the scene to the image at different spatial frequencies, characterizing the overall resolving power and sharpness of the system.

A camera with a 150 mm focal length is flown at 3,000 m above ground level. What is the approximate nominal image scale?

Answer: 1:20,000

Image scale = f/H = 0.150 m / 3,000 m = 1/20,000, giving a scale of 1:20,000.

What does exterior orientation of a photograph define?

Answer: The position and rotational attitude of the camera at the moment of exposure

Exterior orientation defines the six parameters — X, Y, Z position and omega, phi, kappa rotation angles — describing where the camera was and how it was oriented when the photo was taken.

What are the three rotation angles used to describe camera orientation in standard photogrammetric convention?

Answer: Omega, phi, kappa

In photogrammetry, the three rotation angles omega (ω), phi (φ), and kappa (κ) define the rotational orientation of the camera relative to the ground coordinate system.

The collinearity condition in photogrammetry states that:

Answer: An object point, the camera perspective center, and its image point must lie on a single straight line

The collinearity condition states that an object point, the camera's perspective center, and the corresponding image point must lie on the same straight line, which is the fundamental geometric basis of the photogrammetric equations.

Which type of aerial camera lens has an angular field of view greater than 100 degrees and is used for small-scale mapping?

Answer: Superwide-angle lens (about 120°)

Superwide-angle lenses have angular fields of view greater than 100 degrees (typically ~120°), covering large ground areas per photograph, making them suited for small-scale topographic mapping.

What is chromatic aberration in photogrammetric camera lenses?

Answer: The failure of a lens to focus different wavelengths of light at the same focal point

Chromatic aberration occurs when a lens fails to focus all wavelengths of light at exactly the same focal point, causing color fringing or reduced sharpness, particularly visible at high-contrast edges.

In photogrammetric sensor calibration, what is meant by 'self-calibration'?

Answer: Camera interior orientation parameters are solved simultaneously with exterior orientation during bundle adjustment using object-space control

Self-calibration (on-the-job calibration) simultaneously solves for interior orientation parameters and exterior orientation parameters within the bundle adjustment, using highly redundant imagery and ground control points.