Certified Photogrammetrist Stereo Compilation & 3D Modeling 2 — Questions and Answers
Question 1: What is 'relief displacement' in aerial photography?
- The shift of elevated objects outward from the nadir point on a vertical photograph (Correct answer)
- The difference in elevation between two adjacent stereomodels
- The displacement of the horizon line in oblique photography
- The error caused by aircraft crabbing (heading vs. track)
Correct answer: The shift of elevated objects outward from the nadir point on a vertical photograph
Relief displacement is the radial outward shift of elevated objects from the nadir point on a vertical aerial photograph, caused by the perspective projection of terrain relief.
Question 2: What is a TIN (Triangulated Irregular Network) in 3D modeling?
- A point cloud storage format for LiDAR data
- A surface model composed of irregular triangular facets connecting measured mass points and breaklines (Correct answer)
- A raster grid interpolated from contour lines
- A network of GPS base stations for differential correction
Correct answer: A surface model composed of irregular triangular facets connecting measured mass points and breaklines
A TIN is a vector-based surface model made of irregular triangular facets connecting measured points and breaklines, faithfully representing terrain morphology including sharp features like ridges.
Question 3: What is 'breakline' collection in stereo compilation?
- Collecting linear features (ridgelines, drainage lines, roads edges) that define sharp changes in terrain slope for accurate TIN and DEM generation (Correct answer)
- Detecting image matching failures along edges
- Recording the borders between photo strips
- Identifying areas of layover in urban imagery
Correct answer: Collecting linear features (ridgelines, drainage lines, roads edges) that define sharp changes in terrain slope for accurate TIN and DEM generation
Breaklines are collected along ridges, streams, road edges, and other features representing abrupt slope changes, ensuring that TINs and DEMs accurately model terrain discontinuities.
Question 4: What is 'mass point collection' in stereo compilation?
- The systematic collection of random elevation measurements across the terrain to support TIN and DEM generation (Correct answer)
- The collection of coordinate data from heavy-density urban areas only
- Measuring the mass of collected field samples
- Counting the number of control points in the block
Correct answer: The systematic collection of random elevation measurements across the terrain to support TIN and DEM generation
Mass point collection involves systematically measuring a large number of random elevation points across the terrain, providing the raw data needed to build an accurate TIN or DEM surface model.
Question 5: In 3D city modeling, what is 'Level of Detail' (LOD) as defined by CityGML?
- A measure of image resolution used for acquisition planning
- A hierarchical scale of model complexity, from simple block models (LOD1) to fully textured models with interior detail (LOD4) (Correct answer)
- The number of control points used in the block adjustment
- The output file size of the 3D model
Correct answer: A hierarchical scale of model complexity, from simple block models (LOD1) to fully textured models with interior detail (LOD4)
CityGML defines LOD (Level of Detail) as a hierarchy from LOD0 (footprint) through LOD1 (block), LOD2 (roof structures), LOD3 (facades), to LOD4 (interior elements), reflecting increasing geometric complexity.
Question 6: What is 'image rectification' in the photogrammetric workflow?
- Correcting camera interior orientation parameters in the field
- Transforming an image to remove tilt distortion so it appears as if taken from directly above (nadir) (Correct answer)
- Adding color balance between adjacent flight strips
- Reprocessing failed GPS trajectories after landing
Correct answer: Transforming an image to remove tilt distortion so it appears as if taken from directly above (nadir)
Image rectification transforms a tilted aerial photograph to remove tilt effects, producing an image that appears as if taken from directly above—a prerequisite for creating orthophotos.
Certified Photogrammetrist Stereo Compilation & 3D Modeling 2
What is 'relief displacement' in aerial photography?