GNSS Field Navigation
VRGS can take a live position from a GNSS receiver and use it three ways: show you where you are standing on the model, navigate you to a point you picked, and record measurements at the receiver's position rather than where the mouse is pointing.
It is built for taking a laptop or tablet to the outcrop the model was made from — checking an interpretation in front of the rock, walking to a location you chose in the office, and logging a station where you are standing.
What you need
| A receiver on a serial (COM) port | Including USB and Bluetooth receivers, which present themselves as virtual COM ports. Anything that speaks NMEA 0183 works. |
| A project coordinate system | Positions are converted from latitude and longitude into the project's CRS through the project's own PROJ pipeline. Without a CRS, a fix cannot be placed and VRGS says so rather than dropping it at the origin. |
| (Optional) an NTRIP account | For RTK corrections — the difference between a metre-level position and a centimetre-level one. |
The parser is talker-agnostic and handles GGA, RMC, GSA, GSV, VTG, GST and GNS
with checksum validation, so a receiver tracking GPS + GLONASS + Galileo (which
reports $GNGGA rather than $GPGGA) is read correctly.
Connecting
Home → Navigation → Connect GNSS opens the Connect GNSS Receiver dialog.
Receiver
| Field | What it does |
|---|---|
| Find the receiver automatically | Sweep the serial ports and baud rates until something answers. The sweep runs on a background thread, so the application stays responsive. |
| Serial port | Pick the port by its Device Manager name — which is how you tell your receiver from seven other virtual ports. |
| Baud rate | The receiver's rate. Leave auto-detect on if you do not know it. |
| Antenna height (m) | The height of the antenna above the ground, subtracted from the reported height so positions are at your feet, not on top of the pole. |
| Smoothing (epochs) | Average this many position epochs before reporting. Steadier, at the cost of lag when you move. |
RTK corrections (NTRIP)
Tick Stream corrections from an NTRIP caster and fill in:
| Field | What it does |
|---|---|
| Caster / Port | The correction service's address. |
| User name / Password | Your account with that service. |
| Mountpoint | Which base station or network stream to use. Press Get list to fetch the caster's source table and pick from it. |
| Send my position to the caster | Required for network / VRS mountpoints, which generate corrections for wherever you are standing. Leave it off for a single physical base station. |
Corrections are streamed as RTCM3 to the receiver, and the connection reconnects with backoff if it drops.
Replay log
Point Replay log at a recorded NMEA file to drive the whole feature from a file instead of a receiver — useful for rehearsing a survey, demonstrating the workflow indoors, or reproducing a problem.
Reading the solution
The status pane
While a receiver is connected, the status bar carries a live one-line summary — the solution type and the satellite count — so a change in quality is visible wherever you are working. It is blank when nothing is connected.
This matters more than it sounds: an RTK solution can drop from fixed to float — from a couple of centimetres to half a metre — in the middle of a survey, and you want to see that happen.
The in-view display
Two Display Options toggles put a fuller block over the 3D view: the position block, and the satellite list (which is long — leave it off unless you are diagnosing reception).
The block shows only what the receiver actually reported:
GNSS: RTK fixed 18/24 satellites
Corrections: RTCM3, age 1.2 s
Lat 53 28' 12.4" N
Lon 2 14' 05.1" W
Height 142.36 m MSL 190.11 m ellipsoidal
Project 384512.417 E 398221.883 N 142.360 m
Accuracy +/- 0.02 m horizontal, 0.03 m vertical (1 sigma)
| Line | Meaning |
|---|---|
| Solution | Invalid, GPS (standalone), DGPS, RTK float or RTK fixed. Only RTK fixed is centimetre-accurate; RTK float is roughly 0.2–1 m, and standalone GPS is metre-level. |
| Corrections | The correction stream and its age. Corrections that are seconds old are fine; corrections that are tens of seconds old mean the link has stalled and the solution will decay. |
| Project | Your position in the project's coordinate system, which is the number that matters for comparing with the model. |
| Accuracy | The receiver's own 1-sigma error estimate, reported only when the receiver sends one. Where it does not, DOP is shown instead — and labelled as DOP, because satellite geometry is not an accuracy. |
Every value is shown only if the receiver reported it. A blank is "not reported", never a confident zero.
Following your position
Follow GNSS keeps the 3D camera on the live position as it updates, so the view moves with you. Your position is also drawn in the scene as a marker with an accuracy ring, coloured by the fix quality.
Navigating to a point
Showing where you are is not navigation. To walk to something:
- Click the point in the 3D view you want to reach — anywhere on the outcrop, not just an existing object.
- Press Navigate To (Home → Navigation).
- Walk. The display gives you:
| Readout | Meaning |
|---|---|
| Distance | Horizontal distance in project units, with the slope distance where the heights differ. |
| Bearing | Steer n degrees magnetic — derived geodetically from your position and the target's, then converted using the magnetic variation the receiver itself reports. That is the number to set on a compass. The grid and true bearings are shown alongside. |
| Height difference | How far the target is above or below you. |
| Off track | How far you have drifted from the straight line between where you started and the target, and which way to steer to get back on it. |
| ETA | A rough time to walk it, from your current ground speed. |
Stop Navigating clears the target.
"Arrived" is judged against the fix's own error estimate (2 sigma, never finer than a metre) rather than a fixed radius — claiming arrival within a tolerance finer than the receiver can measure would be a fiction. Once you are inside it the bearing is dropped, because at that range the direction is noise.
VRGS shows all three and labels which is which. Steer by the magnetic bearing; the grid bearing is what the project's coordinate system measures, and differs from true north by the grid convergence.
Capturing measurements where you are standing
Three commands record a measurement at the receiver's position instead of under the mouse:
| Command | What it creates |
|---|---|
| Orientation Here | Opens the same dip / dip-direction dialog the one-point orientation tool uses, so you type in what you read off the compass-clinometer. |
| Waypoint Here | A waypoint. |
| Sample Here | A sample point. |
They also appear on the 3D view's GPS menu as Orientation / Waypoint / Sample at GNSS Position.
Nothing is stored in latitude and longitude: the fix is converted to the project CRS on the way in, and the object is stored exactly like a digitised one. Once created, a GNSS-captured measurement is indistinguishable from one you clicked.
A capture that cannot be placed says why — no receiver, no fix yet, no project CRS, or a position outside the CRS's domain — rather than dropping a measurement at the project origin.
The survey quality is recorded
Each capture records the quality it was taken at — the solution type, the satellite count, the receiver's own error estimate (or DOP where it reports none), the correction age and the UTC time — into the object's description. So a station surveyed on RTK fixed can be told apart from one taken on a standalone metre-level fix months later, and Athos can answer "which orientations were surveyed on RTK?".
VRGS warns when a capture is taken on a standalone fix. Half a metre of scatter barely matters for "there is an interesting outcrop here"; it matters a great deal for an orientation station you intend to compare against the model.
Tips and troubleshooting
- Nothing connects. Check the receiver is paired and its virtual COM port exists in Device Manager, then let auto-detect sweep. Some Bluetooth receivers create two ports and only one carries data.
- A fix arrives but nothing appears on the model. The project has no coordinate system, or your position is outside it. Set the project CRS (see Setting the coordinate system).
- The solution never gets past
GPS. Corrections are not reaching the receiver: check the mountpoint, the credentials, and — for a network/VRS mount — that Send my position to the caster is ticked. - It was RTK fixed and dropped to float. Normal under trees, against a cliff face, or when the correction link stalls. Watch the corrections age; wait for it to re-fix before capturing anything you care about.
- The bearing does not match my compass. Check you are reading the magnetic line, not the grid or true one.
- The height looks wrong by a constant amount. Check the antenna height, and whether the project expects orthometric (MSL) or ellipsoidal heights — VRGS keeps both and uses the one that matches the project's vertical datum.