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
What is the primary advantage of LiDAR (Light Detection and Ranging) over photogrammetry for accident scene documentation, and what is its main limitation?
Answer: LiDAR captures accurate 3D data rapidly even in low light and does not depend on surface texture; its main limitation is higher equipment cost compared to camera-based photogrammetry
LiDAR directly measures distances using laser pulses and works in poor lighting without needing surface texture, but the equipment cost is substantially higher than camera-based photogrammetric systems.
When preparing a photogrammetric model for courtroom presentation, what is the advantage of using a textured 3D mesh over a raw point cloud?
Answer: Textured meshes appear more photorealistic and intuitive to jurors, making spatial relationships easier to understand
Applying photographic texture to a mesh creates a visually realistic model that non-technical jurors can interpret more easily than an abstract collection of colored dots.
What does the term 'self-calibration' mean in photogrammetry?
Answer: The photogrammetric software simultaneously estimates camera calibration parameters (focal length, distortion coefficients) during the processing of scene images
Self-calibration allows the software to solve for lens parameters alongside scene geometry, which is particularly useful when pre-calibration was not performed before fieldwork.
A crash occurred on a curve with significant superelevation. How can a photogrammetric DEM help the reconstructionist?
Answer: The DEM provides precise cross-slope and grade measurements that can be used as inputs to vehicle dynamics and critical-speed calculations
Extracting cross-slope (superelevation) and longitudinal grade from a DEM provides accurate roadway geometry inputs needed for friction-based speed and stability calculations.
What is 'georeferencing' in the context of UAV photogrammetry, and how is it typically achieved?
Answer: Associating the photogrammetric model with a real-world coordinate system using GPS-tagged images, ground control points, or a combination of both
Georeferencing links the model to a real-world coordinate system, enabling it to be overlaid on maps and allowing absolute position measurements using GCPs or RTK/PPK GPS.
When a photogrammetric model of a crash scene is completed months after the original investigation, which type of evidence is most critical for validating the model's accuracy?
Answer: Field-measured check points (independent survey coordinates not used in processing) compared against model-extracted coordinates
Independent check points—survey coordinates withheld from processing—provide an objective accuracy assessment by comparing their known positions to model-extracted positions.
In photogrammetric accident reconstruction, what does 'absolute accuracy' mean versus 'relative accuracy'?
Answer: Absolute accuracy describes how closely model coordinates match true real-world coordinates; relative accuracy describes how correctly internal distances and shapes are reproduced within the model regardless of its position in the world
A model can have excellent relative accuracy (correctly proportioned internally) but poor absolute accuracy (incorrectly placed in the world) if georeferencing is weak or absent.