Certified Photogrammetrist Photogrammetric Product Generation 2 — Questions and Answers
Question 1: What is the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) Class 1 horizontal accuracy for 1 cm GSD imagery?
- RMSEx and RMSEy ≤ 1.0 cm, with 95% confidence radius ≤ 1.7 cm (Correct answer)
- RMSEx and RMSEy ≤ 2.5 cm, with 95% confidence radius ≤ 4.3 cm
- RMSEx and RMSEy ≤ 0.5 cm, with 95% confidence radius ≤ 0.9 cm
- RMSEx and RMSEy ≤ 5.0 cm, with 95% confidence radius ≤ 8.6 cm
Correct answer: RMSEx and RMSEy ≤ 1.0 cm, with 95% confidence radius ≤ 1.7 cm
Under ASPRS 2014 standards, Class 1 horizontal accuracy for 1 cm GSD specifies RMSEx and RMSEy ≤ 1.0 cm (equal to the GSD), with a 95% radial confidence of ≤ 1.7 cm.
Question 2: What is 'vertical accuracy' in the context of DEM quality assessment?
- The ability to detect vertical walls in urban areas
- A statistical measure (typically RMSE) of elevation differences between the DEM and ground-truth check points (Correct answer)
- The minimum contour interval achievable from a given GSD
- The number of elevation points collected per square kilometer
Correct answer: A statistical measure (typically RMSE) of elevation differences between the DEM and ground-truth check points
Vertical accuracy for a DEM is typically expressed as the RMSE of elevation differences between DEM values and independently surveyed check points, following standards like ASPRS 2014 or FEMA guidelines.
Question 3: What is a 'mosaic dodging' or 'color balancing' algorithm used for in orthomosaic production?
- Removing GPS positional errors from individual orthophotos
- Adjusting the brightness and color of individual photos to achieve a visually seamless mosaic (Correct answer)
- Detecting and removing cloud shadows from imagery
- Resampling all orthophotos to a common ground pixel size
Correct answer: Adjusting the brightness and color of individual photos to achieve a visually seamless mosaic
Dodging and color balancing algorithms adjust brightness, contrast, and color of individual source orthophotos so that the final mosaic has a uniform appearance without visible lighting differences.
Question 4: What does 'resampling' mean in the context of raster photogrammetric products?
- Re-flying an area to collect additional imagery
- The process of computing pixel values at new grid positions during geometric transformations (e.g., bilinear, cubic convolution) (Correct answer)
- Resampling GPS trajectories to a uniform time interval
- Collecting additional ground control points after initial triangulation
Correct answer: The process of computing pixel values at new grid positions during geometric transformations (e.g., bilinear, cubic convolution)
Resampling computes new pixel values during raster transformation using interpolation methods—nearest neighbor preserves sharp edges, bilinear smooths slightly, and cubic convolution provides the best quality at higher cost.
Question 5: What is 'hypsographic tinting' in topographic map design?
- The use of graduated colors to represent elevation zones, typically from green (lowlands) to brown/white (highlands) (Correct answer)
- The process of digitizing contour lines from stereo imagery
- A color correction technique for multispectral imagery
- The representation of water bodies using blue tints
Correct answer: The use of graduated colors to represent elevation zones, typically from green (lowlands) to brown/white (highlands)
Hypsographic tinting uses a graduated color scheme keyed to elevation, traditionally ranging from green at low elevations through yellow, orange, brown, and white at high elevations to visually communicate terrain relief.
Question 6: In digital orthophoto production, what causes 'smear' artifacts in urban areas?
- GPS positioning errors causing misalignment of adjacent photos
- The use of a DTM (bare-earth) instead of a DSM (full surface) for rectification, causing building rooftops to smear across adjacent areas (Correct answer)
- Excessive JPEG compression during orthophoto tile generation
- Atmospheric haze reducing image contrast in urban areas
Correct answer: The use of a DTM (bare-earth) instead of a DSM (full surface) for rectification, causing building rooftops to smear across adjacent areas
Smear artifacts in urban orthophotos occur when a bare-earth DTM is used for rectification, causing building rooftops—which are elevated above ground—to be incorrectly projected and smeared across adjacent areas.
Certified Photogrammetrist Photogrammetric Product Generation 2
What is the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) Class 1 horizontal accuracy for 1 cm GSD imagery?