Photogrammetric Product Generation Flashcards

What is the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) Class 1 horizontal accuracy for 1 cm GSD imagery?

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.

What is 'vertical accuracy' in the context of DEM quality assessment?

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.

What is a 'mosaic dodging' or 'color balancing' algorithm used for in orthomosaic production?

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.

What does 'resampling' mean in the context of raster photogrammetric products?

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.

What is 'hypsographic tinting' in topographic map design?

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.

In digital orthophoto production, what causes 'smear' artifacts in urban areas?

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.