Photogrammetry Flashcards
7 cards from real ACTAR practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Photogrammetry flashcards as text
In close-range photogrammetry for accident reconstruction, what is the primary purpose of using coded targets or control points?
Answer: To establish a known coordinate system and scale the model accurately
Coded targets or control points provide reference locations with known real-world coordinates, allowing the software to accurately scale and orient the photogrammetric model.
What does 'convergent photography' mean in the context of photogrammetric documentation?
Answer: Capturing multiple overlapping images aimed toward a common subject from different angles
Convergent photography involves taking multiple images from different positions all directed toward the subject, providing the angular diversity needed for 3D reconstruction.
Which type of lens distortion most significantly affects photogrammetric accuracy and must be accounted for during camera calibration?
Answer: Radial (barrel or pincushion) distortion
Radial distortion causes straight lines to appear curved and introduces systematic errors in photogrammetric measurements if not corrected through calibration.
When performing structure-from-motion (SfM) photogrammetry at a crash scene, what minimum overlap is generally recommended between consecutive images?
Answer: 60–80%
At least 60–80% overlap between consecutive images is recommended to ensure sufficient common feature points for reliable 3D reconstruction.
A photogrammetrist notices the point cloud of a crash scene has a significant 'dome' or 'bowl' warping artifact. What is the most likely cause?
Answer: Failure to include oblique or angled images, relying only on nadir (downward-looking) shots
Doming artifacts arise when all images are captured at the same height and angle (nadir-only); adding oblique images at the scene periphery corrects this systematic error.
What is the relationship between ground sampling distance (GSD) and the height at which a UAV captures images for photogrammetry?
Answer: GSD increases as flight altitude increases, meaning lower resolution
As UAV altitude increases, each pixel covers a larger ground area, increasing GSD and reducing the spatial resolution of the final model.
In photogrammetry software, what does the term 'dense point cloud' refer to compared to a 'sparse point cloud'?
Answer: A point cloud containing millions of closely spaced 3D points derived from all image pairs, compared to fewer matched keypoints in a sparse cloud
A dense point cloud is produced by matching pixels across many image pairs to create detailed 3D geometry, while a sparse cloud contains only the initial keypoint matches used to determine camera positions.