Photogrammetric Product Generation Flashcards

What is a 'true orthophoto' as distinct from a standard orthophoto?

Answer: An orthophoto corrected for building lean using a surface model of all above-ground features (DSM), so building walls do not appear in the image

A true orthophoto uses a full DSM (including buildings and trees) for differential rectification, eliminating building lean and wall visibility that appears in standard orthophotos orthorectified using only a DTM.

What is 'differential rectification' in orthophoto production?

Answer: Correcting images pixel-by-pixel using a DEM to remove relief displacement across the entire image

Differential rectification corrects each pixel individually using a DEM, removing the varying relief displacement across the image to produce a geometrically accurate orthophoto.

What does 'contour interval' mean in topographic map production?

Answer: The vertical elevation difference between successive contour lines

Contour interval is the vertical elevation difference between consecutive contour lines on a topographic map, determining the level of vertical detail shown.

For USGS National Map Accuracy Standards, what horizontal accuracy is required for a 1:24,000-scale map?

Answer: ±12.2 meters (40 feet) at the 90% confidence level

USGS NMAS requires that 90% of well-defined points on a 1:24,000-scale map be within ±40 feet (±12.2 meters) of their true position.

What is an 'orthomosaic' in photogrammetric production?

Answer: A single seamless orthophoto created by mosaicking (stitching) multiple overlapping orthophotos together

An orthomosaic is a large, seamless orthophoto produced by mosaicking multiple individual orthophotos, providing wall-to-wall coverage of a project area.

What is 'seam line generation' in orthomosaic production?

Answer: The process of defining boundaries between adjacent orthophotos in a mosaic to minimize visible transitions

Seam line generation defines the boundaries where one source orthophoto transitions to another in the mosaic, with lines typically placed in areas of low contrast (open water, fields) to minimize visible seams.