Surveying Methods & Techniques Flashcards

Which EDM (Electronic Distance Measurement) technique uses the phase difference between emitted and returned electromagnetic waves to determine distance?

Answer: Phase comparison ranging

Phase comparison EDMs measure the phase shift of a continuous modulated wave after it travels to the reflector and back, computing distance from the fractional wavelength difference.

In a two-peg test for a dumpy level, the instrument is found to have a collimation error. The correct adjustment is made so that the line of collimation is:

Answer: Horizontal when the bubble is centered

The line of collimation must be truly horizontal when the instrument is leveled (bubble centered), which is what the two-peg test verifies and corrects.

When computing the area of a parcel using the coordinate method (Gauss formula), the area equals:

Answer: One-half the absolute value of the sum of cross-products of consecutive coordinates

The coordinate (shoelace/Gauss) formula computes area as ½|Σ(Xᵢ(Yᵢ₊₁ − Yᵢ₋₁))|, i.e., half the absolute value of the sum of cross-products of coordinate pairs.

A surveyor establishes a baseline of 500.00 ft and measures angles from each end to an inaccessible point. Angle at station A is 64°30' and angle at station B is 71°15'. Which method is being employed?

Answer: Triangulation (intersection)

Measuring angles to an unknown point from both ends of a known baseline to compute the point's location is the classical triangulation (intersection) method.

LiDAR point cloud data collected from an airborne platform is referenced to ground elevation using:

Answer: Ground control points and GPS/IMU data from the aircraft

Airborne LiDAR uses onboard GPS to track the aircraft position and an IMU (Inertial Measurement Unit) to track orientation; ground control points verify and refine the absolute accuracy.

The 'scale factor' applied in state plane coordinate (SPC) computations accounts for the difference between:

Answer: Grid distance and ground distance

The SPC scale factor (k) converts between ground distance and grid distance: Grid Distance = Ground Distance × k, correcting for the distortion introduced by map projection.

In trigonometric leveling, when measuring elevation differences over long distances, the surveyor must apply corrections for:

Answer: Earth curvature and atmospheric refraction

Over long sight distances, the combined correction for earth curvature (+0.0206 × d²) and atmospheric refraction (−0.0028 × d²) must be applied, yielding a net correction of about +0.0178 × d² (d in miles).