In third order, class I geodetic control, the average triangle closure should not exceed how many arcseconds?

• A. 2 arcseconds
• B. 4 arcseconds
• C. 5 arcseconds
• D. 3 arcseconds

Answer: (D)

Triangulation networks rely on each triangle closing consistently. The triangle closure is the leftover error you get when you complete the loop of a triangle using the measured directions and distances; it shows how well the measurements fit together. For a third-order, class I geodetic control network, the precision target is very tight, so the average closure error across all triangles must be kept small. The standard limit used for this class is three arcseconds, meaning the mean closure error of all triangles should not exceed that value. If the observed average is larger, the network would be re-measured or adjusted to bring it into specification. The other options are not the accepted tolerance for this class, so the three arcseconds value is the conventional benchmark.