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TEC-GIS45-03 · Lesson 5 · 14 clock hours · demo

Real-Time Kinematic (RTK) Concepts and Base-Rover Setup

Objective. Students will set up a GNSS base station over a known control point and configure a rover for RTK corrections, achieving an RTK fixed solution and demonstrating understanding of radio or Bluetooth link requirements.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by an industry-certified professional or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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What Is RTK GNSS?

Real-Time Kinematic (RTK) is a differential GNSS technique that delivers centimeter-level horizontal and vertical accuracy in the field, in real time. A base station receiver sits over a point whose coordinates are precisely known. The base continuously computes the difference between its known position and what its GNSS engine calculates from satellite signals. Those differences — called carrier-phase corrections — are broadcast to a rover receiver over a radio or cellular data link. The rover applies the corrections to its own observations and reports a corrected position, typically within ±2–3 cm under good conditions.

RTK is the backbone of modern survey fieldwork, drone ground control, and construction layout. Understanding it is essential for the NSPS CST exams, everyday surveying practice, and any workflow that feeds data into ArcGIS Pro or a drone mapping pipeline.

Base Station Fundamentals

Occupation Over a Known Control Point

The base must be set up directly over a control monument whose coordinates (latitude, longitude, ellipsoid height, or State Plane northing/easting and NAVD 88 elevation) are already established. Even a small error in the base position propagates into every rover measurement taken during that session. Always verify the monument description and verify that the physical mark matches the project's control network.

Tribrach Leveling and Optical Plummet

Mount the tribrach on a heavy-duty tripod. Center the tribrach over the monument using the optical or laser plummet. Level the circular bubble first with the tripod legs, then fine-level with the tribrach footscrews. Re-check centering after leveling — the two adjustments interact. The antenna phase center must be directly above the monument: lateral offset of even a few millimeters at the base creates a systematic shift in all rover positions.

Antenna Height Measurement

This is the most error-prone step in field GNSS work. You must record the distance from the monument to the antenna's phase center. Two methods are common:

Always use the method specified by the manufacturer for that antenna model. Enter the value into the data collector to at least three decimal places (millimeter resolution). An antenna height blunder is one of the most common causes of vertical errors in final deliverables.

Radio and Cellular Link Requirements

RTK corrections must travel from base to rover with low latency (typically under one second). Two link types are standard:

Whatever link is used, confirm the link status icon on the data collector before recording any points. No link means corrections are not being received.

Float vs. Fixed Solution

When the rover first acquires the base correction stream, it must resolve the integer number of carrier-phase wavelengths between each satellite and the antenna — called integer ambiguity resolution. Until this is resolved, the solution is called float: sub-decimeter accuracy but not survey-grade. Once ambiguities are resolved, the display reads fixed: centimeter-level accuracy. Never record survey-grade data on a float solution. Time to fixed is typically 10–60 seconds under open sky with good satellite geometry; poor multipath or low satellite count can prevent a fixed solution entirely.

Safety on the Survey Range

Workflow Summary

1. Set up and level tribrach over monument.

2. Mount antenna; record slant or vertical height.

3. Power base receiver; enter known coordinates and antenna height.

4. Select radio channel or configure NTRIP; begin broadcasting.

5. At rover, power receiver and data collector; enter same radio channel or NTRIP parameters.

6. Confirm link established; wait for fixed solution.

7. Navigate to each observation point; confirm fixed status before recording.

8. Record solution type and time-to-fixed in field notes.

Key terms10

RTK (Real-Time Kinematic)A differential GNSS technique in which carrier-phase corrections from a base station are transmitted to a rover in real time, enabling centimeter-level positioning accuracy.
Base stationA GNSS receiver set up over a point of known coordinates that computes and broadcasts differential corrections to one or more rovers.
RoverA portable GNSS receiver that receives corrections from a base station or network and reports a corrected, survey-grade position while the operator moves through the field.
Integer ambiguity resolutionThe mathematical process by which the receiver determines the exact whole number of carrier-phase wavelengths between each satellite and the antenna, required to achieve a fixed RTK solution.
Fixed solutionAn RTK position in which integer carrier-phase ambiguities have been fully resolved, yielding centimeter-level accuracy; the only solution type acceptable for survey-grade data collection.
Float solutionAn RTK position in which integer ambiguities have not yet been resolved; accuracy is typically sub-decimeter but not survey-grade — not acceptable for recorded survey observations.
Antenna heightThe measured vertical distance from the survey monument to the antenna's phase center, entered into the data collector so the software can compute ground-level coordinates.
Slant heightThe tape-measured distance from a monument to a defined reference mark on the antenna casing, measured at an angle; must be converted to vertical height using a manufacturer-supplied formula before entry into the data collector.
NTRIP (Networked Transport of RTCM via Internet Protocol)A protocol that allows RTK correction data to be streamed over the internet from a base station or reference network to a rover data collector equipped with a cellular modem.
TribrachA three-screw leveling device that mounts between the tripod head and the instrument or antenna, allowing precise leveling and optical centering over a ground monument.

Worked examples4

1. You measure a slant height of 1.742 m from the monument to the antenna reference notch. The manufacturer states the antenna's slant-to-vertical correction formula is: Vertical Height = √(Slant Height² − Offset²), where the fixed horizontal offset from the monument center to the notch is 0.068 m. What vertical height should you enter in the data collector?
  1. Square the slant height: 1.742² = 3.034564 m²
  2. Square the horizontal offset: 0.068² = 0.004624 m²
  3. Subtract: 3.034564 − 0.004624 = 3.029940 m²
  4. Take the square root: √3.029940 = 1.74069 m
  5. Round to millimeter resolution: 1.741 m
Answer: Enter 1.741 m as the vertical antenna height in the data collector.
2. At the rover, you collect five fixed-solution readings at a single point. The northing values (in meters) are: 5000.013, 5000.009, 5000.011, 5000.014, 5000.008. What is the mean northing and the range of the observations?
  1. Sum the five values: 5000.013 + 5000.009 + 5000.011 + 5000.014 + 5000.008 = 25000.055 m
  2. Divide by 5 to get the mean: 25000.055 ÷ 5 = 5000.011 m
  3. Identify the maximum value: 5000.014 m
  4. Identify the minimum value: 5000.008 m
  5. Compute the range: 5000.014 − 5000.008 = 0.006 m
Answer: Mean northing = 5000.011 m; range = 0.006 m (6 mm), consistent with a good RTK fixed solution.
3. Your base radio is set to transmit on channel 1 at 458.000 MHz. The rover radio is accidentally set to 459.000 MHz. You wait 90 seconds but the data collector shows no link and no RTK corrections. Your colleague suggests switching the rover to channel 1. After switching, how long should you expect to wait for a fixed solution under open-sky conditions before concluding there is a problem?
  1. Confirm the radio channels match (both on channel 1, 458.000 MHz) — this is the prerequisite for any corrections to flow.
  2. Once the link icon confirms corrections are being received, begin timing.
  3. Under open sky with good satellite geometry, a fixed solution typically initializes in 10 to 60 seconds.
  4. If no fixed solution appears after approximately 60–90 seconds under clear sky, investigate: check satellite count (aim for 6 or more), check PDOP (should be below 3.0 for survey work), check for multipath obstructions, and verify the base is actively broadcasting.
Answer: After confirming the link, allow up to about 60 seconds under open sky. If no fixed solution appears by 90 seconds, troubleshoot satellite geometry, obstructions, and base configuration.
4. A student records an antenna height of 1.635 m in the data collector but the actual measured vertical height is 1.640 m. How large is the resulting vertical error in every point collected during that session, and does it meet the 0.005 m tolerance required by the competency check?
  1. Compute the difference: 1.640 m − 1.635 m = 0.005 m
  2. This 0.005 m blunder shifts every collected elevation by 0.005 m (points will appear 5 mm too high because the software thinks the antenna is lower than it really is).
  3. Compare to the tolerance: the competency check requires the entered value to be within 0.005 m of the measured value.
  4. 0.005 m equals exactly the tolerance boundary.
Answer: The vertical error is exactly 0.005 m. This is at the boundary of the allowed tolerance; the entry must be corrected to 1.640 m and all points re-observed to ensure the deliverable meets survey accuracy standards.

The math in this lesson2

Learners convert a 1.742 m slant height with 0.068 m offset to 1.741 m vertical antenna height.
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Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstrates base station setup over a marked control point: tribrach leveling, antenna height measurement (slant vs. vertical height distinction), radio channel selection, and broadcast configuration; students observe and complete a guided note-taking form. · Students work in groups of three to replicate the base setup on a second control monument on the campus survey range, following the manufacturer's step-by-step field procedure; instructor evaluates each group's antenna centering and height measurement. · Rover configuration and link verification: each student on the rover end configures the data collector to receive RTK corrections from the group's base, documents the time-to-fixed-solution, and records the solution type (float vs. fixed) at five offset points around the base.
Materials: Two survey-grade GNSS receivers capable of RTK (base and rover), tripod, tribrach, fixed-height pole, UHF radio link or cellular modem, data collectors, campus survey range control monuments, manufacturer RTK setup guide
Check: Each student must demonstrate correct antenna height entry (within 0.005 m of measured value), achieve a fixed RTK solution independently, and record five valid fixed-solution observations; any incorrect antenna height entry requires immediate correction and re-demonstration.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NSPS CST — GNSS Technology and Field Procedures
1. In an RTK system, what is the primary purpose of the base station?
NSPS CST — Measurements and Calculations
2. A field crew measures a slant height of 1.800 m and uses the formula Vertical Height = √(Slant² − Offset²) with a 0.060 m horizontal offset. Which value should be entered into the data collector?
NSPS CST — GNSS Technology and Field Procedures
3. A rover data collector displays 'Float' after 15 seconds of receiving corrections. What is the correct action before recording a survey point?
NSPS CST — Instrument Setup and Care
4. During base station setup, the optical plummet shows the instrument is centered, but the circular bubble is not leveled. What is the correct sequence to resolve this?
NSPS CST — GNSS Technology and Field Procedures
5. Which condition is most likely to prevent a rover from achieving a fixed RTK solution even when the radio link is confirmed active?
FAA Part 107 — Airspace Classification and Authorization
6. Under FAA Part 107, a remote pilot planning to use RTK GNSS to collect ground control points for a drone mapping mission must ensure the drone operation complies with airspace authorization requirements. Which tool does the FAA provide for remote pilots to check controlled airspace and request authorization?
NSPS CST — Measurements and Calculations
7. A student accidentally enters an antenna height of 1.520 m when the measured vertical height is 1.527 m. What is the magnitude of the resulting systematic vertical error in all collected points?
Esri ArcGIS Pro — Data Management and Quality Control
8. When collecting GIS field data using RTK GNSS, which ArcGIS Pro data management practice best preserves the accuracy metadata of each collected point?
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