Field Procedures & Data Collection Flashcards

Before measuring EDM distances with a total station, which atmospheric values should be entered to compute the correction?

Answer: Temperature and barometric pressure

Temperature and pressure affect the speed of light in air, which changes measured distances.

Why are angles often measured in both face left and face right (direct and reverse)?

Answer: To cancel instrument errors such as collimation and trunnion axis error

Averaging direct and reverse readings removes most systematic instrument axis errors.

If the prism constant in the total station doesn't match the prism being used, what happens to the measured distances?

Answer: Every distance is off by the same constant amount

A prism constant mismatch adds a fixed offset to every distance measured.

After orienting a total station on a backsight, what is the best field check before collecting data?

Answer: Measure to a second known control point and compare coordinates

Shooting an independent known point checks the setup, orientation, and point coordinates.

Why are construction stakes often set at an offset from the actual design location?

Answer: So they survive excavation and grading at the design location

Offset stakes stay intact while equipment works the actual alignment and can be used to re-establish it.

A grade stake is marked "C 2.5". What does this tell the contractor?

Answer: Cut 2.5 ft to reach design grade

"C" means cut, so the existing ground is 2.5 ft above design grade at that point.

Which is the most important requirement for a leveling turning point?

Answer: It must be stable and well defined for both the foresight and next backsight

Any movement of the turning point between the foresight and backsight puts an error directly into the elevations.