Certified Photogrammetrist Photogrammetric Product Generation

Question 1

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

Accepted 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

Answer

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.

Question 2

What is 'differential rectification' in orthophoto production?

Accepted Answer

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

Answer

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

Question 3

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

Accepted Answer

The vertical elevation difference between successive contour lines

Answer

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

Question 4

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

Accepted Answer

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

Answer

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.

Question 5

What is an 'orthomosaic' in photogrammetric production?

Accepted Answer

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

Answer

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

Certified Photogrammetrist Practice Test

Certified Photogrammetrist Practice Test

Certified Photogrammetrist Photogrammetric Product Generation