GPS Positioning Methods

What is static GPS surveying?

Receivers remain stationary for extended periods (1-4 hours). Provides highest accuracy through long observation sessions and strong geometry.

What is rapid static surveying?

Shorter observation times (5-20 minutes) using advanced ambiguity resolution algorithms. Suitable for moderate baseline lengths.

What is kinematic GPS?

One receiver (base) stationary, another (rover) moving. Provides centimeter-level positions for each observation epoch.

What is RTK?

Real-Time Kinematic - base station transmits corrections to rover for instant centimeter-level positions. Limited by radio range and latency.

What is a fixed solution?

Carrier phase solution where integer ambiguities are resolved to whole numbers. Provides centimeter-level accuracy.

What is a float solution?

Carrier phase solution where ambiguities are real numbers rather than resolved integers. Accuracy is typically decimeter-level.

What is initialization in kinematic GPS?

Process of resolving integer ambiguities at the start. Methods: static initialization, known point, or on-the-fly (OTF).

What is On-The-Fly (OTF)?

Ambiguity resolution while receiver is moving, enabling continuous kinematic positioning without stopping at known points.

What is a baseline in GPS?

Vector connecting two GPS stations, defined by coordinate differences (ΔX, ΔY, ΔZ). The fundamental observable in relative positioning.

What is RINEX?

Receiver Independent Exchange Format - standard ASCII format for GPS observation data enabling exchange between manufacturers.

What is a trivial baseline?

A baseline mathematically dependent on other baselines in a session. Should be excluded from network adjustments.

What is a session in GPS?

Period of simultaneous GPS data collection. Multiple sessions with different geometry improve network accuracy.

What is PPP?

Precise Point Positioning - uses precise orbits and clocks for decimeter to centimeter accuracy from single receiver, without base station.

What is RTN?

Real-Time Network - uses multiple reference stations to generate network-based corrections, extending RTK coverage and reliability.

What is VRS?

Virtual Reference Station - RTN technique creating synthetic reference station data near the rover, simplifying operation.

What is PPK?

Post-Processed Kinematic - similar to RTK but corrections applied after data collection rather than in real-time.

What is the base station in RTK?

GPS receiver at known location broadcasting corrections to rovers. Should be on stable control point with good sky visibility.

What is the rover in RTK?

Mobile GPS receiver collecting data at unknown points, receiving corrections to determine centimeter-level positions.

What is OPUS?

Online Positioning User Service - NGS service for processing GPS data for precise positioning using CORS network.

What is CORS?

Continuously Operating Reference Station - permanent GPS base station providing correction data for post-processing and real-time networks.

What is epoch in GPS?

A specific moment when GPS observations are recorded. Modern receivers record at 1 Hz or faster.

What factors affect baseline accuracy?

• Observation time • Satellite geometry • Baseline length • Atmospheric conditions • Multipath environment

What is the typical accuracy of static GPS?

1-10 mm horizontal, 2-20 mm vertical for baselines under 20 km with 1+ hour observations.

What is the typical accuracy of RTK?

1-2 cm horizontal, 2-3 cm vertical when fixed, within range of base station (typically <10-20 km).

When should you use static vs RTK?

Static: Control networks, high-accuracy requirements, long baselines RTK: Construction staking, topographic surveys, rapid field work

What causes an RTK float instead of fix?

• Poor satellite geometry • Multipath • Long baseline • Atmospheric conditions • Cycle slips • Radio signal issues

What is network RTK geometry advantage?

Multiple reference stations model atmospheric effects across area, improving accuracy and range compared to single base RTK.

What is the maximum practical RTK baseline length?

Typically 10-20 km for single base. Network RTK can extend coverage statewide with maintained accuracy.

How does PPP differ from RTK?

PPP uses precise orbits/clocks (no base station) but requires 20+ minutes convergence. RTK uses local base for instant centimeter positions.