ACTAR Photogrammetry 4

Question 1

Which of the following best describes 'orthorectification' in photogrammetric products?

Accepted Answer

Correcting an image to remove perspective distortion and terrain relief displacement so it has a uniform scale throughout

Answer

Orthorectification corrects perspective distortion and displacement caused by terrain elevation changes, producing an orthophoto where all pixels have the same ground scale.

Question 2

A reconstructionist needs to determine the pre-impact position of a vehicle using photogrammetric analysis of surveillance video. What unique challenge does video photogrammetry present compared to still photography?

Accepted Answer

Video frames have lower resolution and may have rolling shutter distortion, complicating accurate 3D reconstruction

Answer

Video frames are typically lower resolution than still photos and CMOS sensors in cameras often exhibit rolling shutter artifacts that cause geometric distortions requiring correction.

Question 3

What is a 'digital elevation model' (DEM) in the context of photogrammetric outputs, and why is it useful in accident reconstruction?

Accepted Answer

A raster dataset representing the height of the ground surface at each pixel location, useful for analyzing road grade and superelevation

Answer

A DEM captures terrain height information across the scene, enabling reconstructionists to measure road grades, superelevation, and drainage patterns relevant to vehicle dynamics.

Question 4

When using photogrammetry to document tire marks, why is it important to photograph them before any rain or road cleaning occurs?

Accepted Answer

Moisture and cleaning can obliterate or alter the physical evidence, making accurate photogrammetric documentation impossible afterward

Answer

Tire marks are transient physical evidence that can be washed away or degraded quickly; photogrammetric documentation must occur before any environmental or human alteration.

Question 5

What is the purpose of the 'scale bar' in close-range photogrammetry when GPS or total station control points are unavailable?

Accepted Answer

To provide a known physical length that allows the software to determine the real-world scale of the model

Answer

A scale bar with a precisely known length placed in the scene allows photogrammetry software to convert model units to real-world measurements when GPS control is not used.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Photogrammetry 4