DEV Community: Eview GNSS

How to Test RTK Under Trees: A Practical Checklist with RTKLIB

Eview GNSS — Mon, 26 Oct 2026 16:38:03 +0000

Anyone who has run RTK near trees knows the status bar can flip from FIX to FLOAT for no obvious reason. If you are choosing a receiver for an orchard robot, a lawn mower, a forestry survey or an outdoor AMR, you need a test that tells you how it will behave under canopy, not a brochure number measured in an open field.

We recently reviewed a multi-receiver field test logged under roadside trees in rain. The results were interesting: three of four record groups held a 100% fixed solution for 39–61 minutes, while one dropped to 83–89%. The review also showed how easy it is to draw the wrong conclusion from data like this. This checklist is what we would do differently next time.

1. Decide what "good" means before you start

Fix ratio alone is not enough. Write down the metrics you will report:

Fix ratio: share of epochs with a fixed RTK solution (Q=1 in RTKLIB)
Accuracy: horizontal and vertical RMS and 95th percentile against a known truth
Time to first fix after a cold start and after losing the fix
Availability: share of epochs with any usable solution

A receiver that reports 100% fixed but sits 10 cm off the truth is worse than one that reports 95% fixed and is right.

2. Get a truth

Without a truth, you are only comparing status flags. Options:

A surveyed control point with known coordinates in a stated frame
A long static session post-processed against a nearby CORS station

Put the antenna on the control point, or measure the offset precisely.

3. Control the variables

The review we looked at changed canopy, baseline, site, correction source and weather between sessions, so no single factor could be blamed for a difference. Avoid that:

Keep the same	Vary on purpose
Site and antenna position	Open sky vs under canopy
Baseline and correction source	Dry vs wet
Receiver settings and firmware	(one factor at a time)

Repeat every combination at least three times, ideally on different days, so you see the effect of satellite geometry.

4. Log raw data, not just screenshots

Log raw observations (RINEX, or the receiver's native format such as SBF) and the solution file. With raw data you can:

Reprocess every receiver with the same engine and settings in RTKLIB (rnx2rtkp or RTKPOST)
Check whether fix decisions were correct
Reproduce plots later instead of relying on screenshots

Also log: antenna height, canopy photos, rain intensity, firmware version, elevation mask, ambiguity resolution mode, satellites used, PDOP and C/N0.

5. Plot with RTKPLOT

RTKPLOT (part of RTKLIB) is the quickest way to see what happened:

Ground track view: fixed points (Q=1) should form a tight cluster or a clean path; float (Q=2) and DGPS (Q=4) show up as scattered jumps.
Position view: E, N and U against time, which shows when the fix was lost and how big the jumps were.
Nsat view: satellites used over time, which helps explain dropouts under canopy.

Its status bar gives the epoch count N and the Q=1/Q=2/Q=4 split. Note those numbers for each file; they are your fix ratio.

6. Use enough units

One unit per model cannot separate model performance from unit-to-unit variation. Use at least two units per model, and on dual-antenna receivers log heading at the same time, since heading is often what fails first under canopy.

7. Handle the statistics honestly

At 10 Hz, neighbouring epochs are strongly correlated, so 36,000 epochs is not 36,000 independent samples. Decimate to 1 Hz before computing statistics, state the effective sample size, and don't build confidence intervals from raw N.

8. Report what you can and cannot conclude

A good test report says clearly:

What was controlled and what was not
Which device produced which file (by serial number)
Whether the conclusion is about status (fix ratio) or accuracy (error vs truth)

The field review behind this checklist

The review that prompted this checklist covers 36 screenshots from three sessions (half sky + rain, under trees + rain, and under trees with network RTK), with Septentrio mosaic-X5 and mosaic-H receivers as used in the Eview HB56 and HB56H. It includes the full fix-ratio tables, the figures and a retest design:

RTK Fix Ratio Under Tree Canopy and Rain: Field Review

Disclosure: I work with Eview GNSS. Test data was supplied by the test team and is used with permission. RTKLIB is open source: rtklib.com.

GNSS With Heading: How Dual-Antenna Heading Works (Engineer's Guide)

Eview GNSS — Wed, 14 Oct 2026 11:03:26 +0000

Originally published at gnss-solutions.com.

Short answer: a GNSS receiver with heading uses two antennas a known distance apart and compares their carrier-phase signals to measure the direction the vehicle points, even when it is stationary. With a 1 m baseline, Septentrio-based receivers reach about 0.15°, and longer baselines are more accurate. Eview heading receivers include the HB6 Pro, HB52H and HB10.

Updated October 2026.

Dual antenna GNSS heading is a technique that measures a vehicle's orientation (yaw angle) by comparing the carrier-phase signals from two GNSS antennas mounted a fixed distance apart on the same platform. Because it derives direction from satellite geometry rather than the Earth's magnetic field, it needs no compass, no moving parts, and keeps providing heading even when the vehicle is stationary. Eview's Septentrio-powered GNSS receiver box adds AIM+ anti-jamming so heading stays available near steel structures and powerlines.

How Dual Antenna GNSS Heading Works

A dual-antenna heading receiver uses two RF inputs connected to antennas separated by a precisely known baseline — typically 0.5–2 m on vehicles, longer on vessels. Both antennas track the same satellites, and the receiver measures the carrier-phase difference between the two signals for each satellite. The phase difference encodes the baseline's direction, which the receiver resolves into east/north components and converts to heading.

The hard part is resolving integer carrier-phase ambiguities — the unknown whole number of wavelengths in each measurement. RTK solves the same problem; here the receiver simply differences the two antennas against each other rather than against an external base station. Multi-constellation, multi-frequency tracking (GPS, GLONASS, Galileo, BeiDou on L1/L2/L5 and E1/E5) supplies enough redundant measurements to fix ambiguities in seconds, and because both antennas share one receiver clock, common errors cancel out of the baseline solution.

Dual Antenna vs. Compass, COG, and Single-Antenna Solutions

A magnetic compass measures the magnetic field, not true north: ferrous hulls, motors, battery currents, and powerlines all bend the field. Course over ground from a single antenna works only while moving and collapses at low speed. IMU gyros supply rate data but drift unless continuously aided.

Dual antenna GNSS heading is an absolute measurement referenced to the satellite constellation: immune to magnetic interference, available at zero speed, stable under acceleration and vibration. That is why it is the preferred heading source for autonomous robots and construction machine control, where GNSS keeps an IMU-aided filter drift-free.

Where Dual Antenna GNSS Heading Is Used in Industry

Every application shares one trait: a machine must know which way it is pointing with no human in the loop. On marine vessels, dual-antenna receivers feed autopilots and dynamic positioning. In construction and mining, dozers, graders, and pavers use them so blades follow the design surface even in reverse, and agricultural robots steer accurately across row crops without gyro drift.

Larger UAVs, eVTOL aircraft, and drone RTK systems use it for orientation during pre-takeoff alignment and in GNSS-challenged corridors. Interference-heavy environments are exactly where Septentrio's AIM+ technology matters: anti-jamming GNSS receivers keep producing valid heading where standard receivers lose lock.

How Accurate Is Dual Antenna GNSS Heading?

Heading accuracy scales with baseline length: a longer antenna separation produces a larger phase difference for the same angular change, so the same carrier-phase noise maps to a smaller angle error. A professional dual-antenna receiver typically achieves 0.1–0.3° RMS with a 1 m baseline, improving to well under 0.1° with a 2 m baseline and multi-frequency tracking. Multipath is the main enemy — reflections corrupt carrier phase at both antennas — so receiver-level mitigation matters as much as the antenna pair itself.

Septentrio-based receivers such as the mosaic-X5 and AsteRx series used in Eview products output heading at up to 100 Hz and re-acquire it almost instantly after signal loss. Paired with survey-grade GNSS antennas, the baseline mounting accuracy becomes the practical limit.

Choosing a Dual-Antenna GNSS Receiver

The receiver must have two phase-coherent RF inputs sampled from one clock — two separate single-antenna receivers cannot produce a meaningful baseline. It should track all constellations on multiple frequencies for fast ambiguity resolution and output heading at 10–100 Hz. Match it to the environment: Septentrio-powered OEM boards bring AIM+ anti-jamming and anti-spoofing to compact embedded designs, while rugged enclosure receivers suit vehicles and vessels needing IP-rated hardware out of the box.

Eview GNSS receivers with heading

Eview receiver	Septentrio module	Best for
HB6 Pro	mosaic-H	Dual-antenna RTK and heading in a compact receiver
HB56H	mosaic-H	Heading with SD card logging
HB52H, HB50H, HB51	mosaic-G5 P3H	Light, low-power heading for drones and small robots (0.15° at 1 m)
HB10	AsteRx-m3 Pro+	Heading at up to 100 Hz for fast vehicles

Tell us your vehicle, antenna spacing and update-rate needs and we will recommend a heading receiver: sales@gnss-solutions.com. Datasheets and manuals are sent by email.

FAQ: Dual Antenna GNSS Heading

What is a GNSS receiver with heading? It is a GNSS receiver that outputs the direction a vehicle is pointing (heading or yaw) as well as its position, by using two antennas a known distance apart. Unlike a compass it is not affected by magnetic disturbance, and unlike course-over-ground it works when the vehicle is stationary.

What is dual antenna GNSS heading? It computes a vehicle's orientation by comparing carrier-phase measurements from two GNSS antennas mounted a known distance apart. The receiver resolves the baseline vector between the antennas and derives heading — no compass, no moving parts, and it works at standstill.

How accurate is dual antenna GNSS heading? With a 1 m baseline, professional receivers typically achieve 0.1–0.3° RMS in good conditions; longer baselines and multi-frequency, multi-constellation tracking push accuracy below 0.1°. Multipath and mounting errors, not receiver noise, usually dominate in real installations.

Does dual antenna GNSS heading work when the vehicle is stationary? Yes. Heading comes from instantaneous carrier-phase differences between two antennas, not from motion, so it is available at zero speed — a key advantage over single-antenna course over ground.

Do I need RTK corrections for dual antenna GNSS heading? No. Heading is a relative measurement between the two antennas, so it needs no external base station or correction stream. If the platform also needs centimeter-level position, the same receiver can run RTK or PPP on the primary antenna.

How far apart should the two antennas be? Longer baselines give better heading accuracy but are limited by the platform. Vehicles and robots typically use 0.5–2 m; vessels and large machines can use several meters. The baseline is surveyed or auto-calibrated during installation.

Which GNSS receivers support dual antenna heading? Any receiver with two phase-coherent RF inputs and dual-antenna firmware, such as the Septentrio mosaic-X5 and AsteRx-series modules used in Eview GNSS receivers, whose AIM+ mitigation keeps heading available in jamming and high-multipath environments.

Disclosure: I work at Eview GNSS, which designs receivers powered by Septentrio modules.

RTK vs PPK for Drone Mapping: Which to Use? (2026)

Eview GNSS — Sun, 11 Oct 2026 02:57:16 +0000

Originally published at gnss-solutions.com.

Short answer: Choose RTK when you need centimetre accuracy in real time and you can count on a correction link for the whole flight. Choose PPK when that link may drop — hilly terrain, long range, urban canyons — because accuracy can be recovered afterwards. Most professional mapping crews run both at once: RTK for live pilot feedback, simultaneous raw logging as a PPK safety net.

If you fly drones for mapping, surveying, or inspection, you have two options for achieving centimeter-accurate positioning: RTK (Real-Time Kinematic) and PPK (Post-Processed Kinematic). Both use the same underlying principle — differential corrections from a base station — but they apply those corrections at different points in the workflow. This guide explains the trade-offs and helps you choose the right approach.

How RTK Works (Real-Time Corrections)

RTK applies corrections during the flight. The base station (or NTRIP caster) transmits RTCM correction data to the drone over a real-time data link — typically 4G/LTE cellular or a dedicated radio modem at 433/868/915 MHz. The drone’s GNSS receiver combines these corrections with its own satellite observations and computes a centimeter-accurate position in real time.

Advantages of RTK:

Immediate results: You know your accuracy during the flight. The pilot sees “RTK Fixed” on the controller and can verify data quality before landing.
No post-processing: Geotagged images are ready to import into photogrammetry software immediately after the flight.
Real-time QA: If the correction link drops mid-flight, the pilot knows immediately and can adjust the flight plan or abort.

Disadvantages:

Requires a correction link: If you lose cellular connectivity (hills, remote areas, low altitude) or exceed radio range, you lose RTK.
No recovery: If the link drops for 30 seconds during an important pass, those images may have degraded accuracy with no way to fix them.
Cellular costs: NTRIP via 4G requires a data plan and coverage in the operation area.

How PPK Works (Post-Processed Corrections)

PPK records raw GNSS observations on the drone during flight (RINEX format) while a base station simultaneously records data on the ground. After landing, the raw drone data is post-processed against the base station data using PPK software (RTKLIB, Trimble Business Center, etc.). The software computes the drone’s precise trajectory for each epoch.

Advantages of PPK:

No correction link needed: The drone flies completely untethered. No cellular, no radio modem, no NTRIP subscription.
Recoverable accuracy: Even if the drone briefly loses satellite lock, the post-processed solution can use forward/backward smoothing to recover position.
Works anywhere: As long as both drone and base station record data, PPK works in deep valleys, remote mountains, and urban canyons where cellular and radio links fail.

Disadvantages:

Post-processing time: You cannot verify accuracy until after the flight and processing.
Requires a base station: You either need a physical base station at the site or a Virtual Reference Station (VRS) from a correction service.
Additional software: PPK processing adds a step to your workflow and requires familiarity with post-processing tools.

RTK vs PPK: Side by Side

Factor	RTK	PPK
Accuracy	1-3 cm	1-3 cm (potentially slightly better with smoothing)
Correction link needed	Yes (cellular or radio)	No
Real-time feedback	Yes — “RTK Fixed” status	No — must process after flight
Post-processing	None	Required (10-30 min per flight)
Reliability	Dependent on link quality	High — independent of link
Best for	Open areas with good cellular	Remote areas, hilly terrain, urban
Equipment cost	Similar (bundle with data plan)	Similar (add PPK software cost)

The Best Approach: Use Both

Most professional drone mapping operators use both RTK and PPK. Here is the typical workflow:

Connect RTK via NTRIP during flight for real-time accuracy feedback
The receiver simultaneously logs raw RINEX data to onboard storage
If RTK stays fixed for the entire flight — use the real-time geotags directly
If the RTK link drops — process the RINEX data with PPK to recover accuracy
Cross-validate both solutions before final deliverable

Septentrio mosaic GNSS receivers, available in Eview receiver boxes, support simultaneous RTK output and RINEX logging natively — no additional hardware required.

Doing Both From One Receiver

You do not need two payloads, or two flights, to get RTK and PPK. On a Septentrio mosaic-based receiver the two run side by side by design: the receiver outputs RTK-corrected positions to the autopilot in real time while writing its own raw observations to storage. If the correction link holds for the whole flight you use the real-time solution; if it drops on the pass that matters, you post-process the raw file and recover full accuracy.

Two Eview options cover most drone mapping builds:

HB52 / HB52H — ultralight RTK receiver with onboard logging. Outputs standard NMEA and Septentrio SBF, and logs complete raw measurements to a microSD card (up to 32 GB) while running RTK. SBF converts to RINEX for PPK workflows, so the same flight gives you a live solution and a post-processable one. The HB52H adds dual-antenna heading.
HBEV322 / HBEV322H — compact RTK receiver and antenna in one. The smallest all-in-one option, with raw carrier-phase output in Septentrio SBF. Best where payload weight and mounting space are the constraint.

Both are built on Septentrio mosaic modules, so both carry AIM+ anti-jamming — the feature that matters when you fly near power lines, substations or urban RF clutter, where a correction link is not the only thing that can fail. For the ground side, pair either with a base station logging RINEX for a fully independent PPK chain.

Frequently Asked Questions

What is the difference between RTK and PPK for drone mapping?

RTK applies corrections live during flight. PPK applies them after the flight in software.

Which is better for drone mapping, RTK or PPK?

Neither is universally better. RTK for immediate results with reliable link. PPK for all-terrain reliability. Both for professional workflows.

Does RTK or PPK produce more accurate results?

Both achieve 1-3 cm. PPK can be slightly better due to forward/backward smoothing, but the difference is negligible in practice.

Can a drone do both RTK and PPK?

Yes. Septentrio mosaic-based receivers output real-time RTK while logging RINEX simultaneously — best of both worlds.

Do I need ground control points with RTK or PPK?

Reduced to 1-3 validation points. Not eliminated entirely, but significantly fewer than non-RTK/PPK workflows. See how to choose a GNSS receiver for surveying.

What equipment do I need for RTK vs PPK drone mapping?

Similar drone hardware. RTK adds a live correction link (4G/radio). PPK adds post-processing software. Both need a base station or VRS.

Drone & UAV RTK GNSS Solutions | Eview GNSS Receiver Box | GNSS News & Updates

Not sure which fits your drone? Email sales@gnss-solutions.com with your platform and accuracy target, and we’ll recommend a receiver.

I work at Eview GNSS, where we build RTK and dual-antenna heading receivers on Septentrio modules. Questions about RTK or PPK setups are welcome in the comments.