Certified Photogrammetrist Quality Control & Standards in Photogrammetry 1 — Questions and Answers
Question 1: What does the ASPRS 2014 standard use instead of the traditional NMAS 90% circular error to define accuracy?
- Probable error (PE50)
- RMSE-based accuracy with separate thresholds for horizontal (RMSEx, RMSEy) and vertical (RMSEz) components (Correct answer)
- Standard deviation of ground control residuals only
- Maximum allowable error for any single check point
Correct answer: RMSE-based accuracy with separate thresholds for horizontal (RMSEx, RMSEy) and vertical (RMSEz) components
ASPRS 2014 replaced the circular error approach with RMSE-based accuracy metrics, separately specifying RMSEx, RMSEy, and RMSEz thresholds that are tied to the product's GSD or contour interval.
Question 2: What is the minimum number of independent check points recommended by ASPRS 2014 for a small project area (< 500 km²)?
- 5 check points
- 20 check points
- At least 20 well-distributed independent check points (Correct answer)
- 100 check points per map sheet
Correct answer: At least 20 well-distributed independent check points
ASPRS 2014 recommends a minimum of 20 well-distributed independent check points for assessing accuracy on smaller project areas, ensuring statistical validity of the reported accuracy.
Question 3: What is 'QA/QC' in the context of a photogrammetric mapping project?
- Quick Acquisition / Quality Collection — field data collection protocols
- Quality Assurance (process controls) and Quality Control (product inspection and testing) to ensure deliverables meet specifications (Correct answer)
- Quantitative Analysis / Qualitative Calibration of sensor data
- The flight plan review process before data acquisition
Correct answer: Quality Assurance (process controls) and Quality Control (product inspection and testing) to ensure deliverables meet specifications
QA/QC encompasses Quality Assurance (systematic processes that prevent defects) and Quality Control (inspection and testing activities that detect and correct defects) in the production of photogrammetric deliverables.
Question 4: What is a 'metadata report' required to accompany photogrammetric deliverables?
- A financial invoice detailing all project costs
- Documentation describing data acquisition parameters, processing methods, datum/projection, accuracy, and data quality information (Correct answer)
- A list of all software licenses used in production
- A photographic log of the camera operator's activities
Correct answer: Documentation describing data acquisition parameters, processing methods, datum/projection, accuracy, and data quality information
Metadata reports document all relevant information about data acquisition and processing—including flight parameters, camera calibration, datum, projection, accuracy statistics, and lineage—enabling proper use and archiving of deliverables.
Question 5: What is 'vertical datum' and why is it critical in photogrammetric elevation products?
- The minimum flight altitude allowed by aviation regulations
- The reference surface (e.g., NAVD 88, NGVD 29, ellipsoid) to which all elevations are referenced, determining how heights interoperate with other datasets (Correct answer)
- The maximum allowable vertical error in the DEM product
- The elevation of the base station used for GPS differential correction
Correct answer: The reference surface (e.g., NAVD 88, NGVD 29, ellipsoid) to which all elevations are referenced, determining how heights interoperate with other datasets
The vertical datum defines the reference surface (e.g., NAVD 88 in the US) to which all elevations are referenced; using an incorrect or undocumented datum causes systematic elevation offsets when data is integrated with other height information.
Question 6: What is 'data completeness' as a dimension of geospatial data quality?
- The percentage of image pixels with valid radiometric values
- The degree to which all required features and attributes are present and correctly represented in the dataset (Correct answer)
- The number of check points used to assess accuracy
- The ratio of collected mass points to the project area
Correct answer: The degree to which all required features and attributes are present and correctly represented in the dataset
Data completeness measures whether all required features, objects, and attributes are present in the dataset without omissions or commissions, as specified by the product standard or project specification.
Certified Photogrammetrist Quality Control & Standards in Photogrammetry 1
What does the ASPRS 2014 standard use instead of the traditional NMAS 90% circular error to define accuracy?