Certified Photogrammetrist Digital Photogrammetry & Point Clouds

Question 1

What algorithm is most commonly used for automatic image matching to generate dense point clouds?

Accepted Answer

Semi-Global Matching (SGM) or Multi-View Stereo (MVS)

Answer

Semi-Global Matching (SGM) and Multi-View Stereo (MVS) are the dominant algorithms for dense image matching that produce high-density point clouds from overlapping photographs.

Question 2

What is 'ground sample distance' (GSD) in digital photogrammetry?

Accepted Answer

The real-world size represented by one pixel in the image

Answer

GSD (Ground Sample Distance) is the real-world dimension represented by a single pixel in the image, determining the spatial resolution of the final mapping products.

Question 3

Which type of point cloud classification separates ground returns from vegetation and structures?

Accepted Answer

LAS class 2 (ground) filtering using algorithms like Progressive TIN or CSF

Answer

Ground classification assigns LAS class 2 to bare-earth returns using algorithms like Progressive Triangulated Irregular Network (PTIN) or Cloth Simulation Filter (CSF) that distinguish ground from above-ground features.

Question 4

What is a Structure from Motion (SfM) workflow in photogrammetry?

Accepted Answer

A process that reconstructs 3D structure and camera positions simultaneously from unordered image sets

Answer

Structure from Motion (SfM) simultaneously estimates 3D scene structure and camera position/orientation from a set of overlapping images, regardless of their initial order or known camera positions.

Question 5

In a LiDAR or photogrammetric point cloud, what does 'point density' measure?

Accepted Answer

The number of points per unit area (e.g., points per square meter)

Answer

Point density is the number of points per unit area (typically points/m²), which determines the level of surface detail and the accuracy of derived products like DEMs.

Certified Photogrammetrist Practice Test

Certified Photogrammetrist Practice Test

Certified Photogrammetrist Digital Photogrammetry & Point Clouds