GPS and Field Data Collection Flashcards

What is the minimum number of GPS satellites required to calculate a 3D position fix (latitude, longitude, and elevation)?

Answer: 4

A minimum of four satellites is required for a 3D GPS fix — three to solve for the three position coordinates and a fourth to eliminate clock error in the receiver.

Differential GPS (DGPS) improves positional accuracy by:

Answer: Applying correction signals from a stationary base station at a known location

DGPS uses a fixed reference receiver at a precisely surveyed location to compute positional errors and broadcast real-time corrections to roving GPS receivers in the field.

Which GPS error source results from signals bouncing off nearby buildings, vehicles, or terrain before reaching the receiver antenna?

Answer: Multipath error

Multipath error occurs when GPS signals reflect off nearby surfaces and travel longer indirect paths to the receiver, causing inaccurate pseudorange measurements.

What does Dilution of Precision (DOP) measure in GPS surveys?

Answer: The geometric quality of available satellite configuration affecting positional accuracy

DOP quantifies how satellite geometry affects positional accuracy — a low DOP value (closer to 1) indicates favorable satellite spread and more precise positioning.

Real-Time Kinematic (RTK) GPS achieves centimeter-level accuracy by:

Answer: Using carrier phase measurements and a real-time base station correction link

RTK GPS resolves integer ambiguities in carrier phase measurements using real-time corrections from a base station, enabling centimeter-level accuracy in the field.

In GIS field data collection, which file format is the native exchange format for GNSS waypoints, routes, and tracks commonly supported by handheld GPS devices?

Answer: GPX (GPS Exchange Format)

GPX is an open XML-based format designed specifically for GPS data — it stores waypoints, tracks, and routes and is supported by virtually all GPS devices and many GIS applications.