AgOpenGPS RTK Position Setup: Connect a Kalmix SCOUT PRO over USB Serial
A field edge is a poor place to discover that Windows has renamed a COM port. The Windows and AgIO configuration can be settled at a desk before you go outside.
Verified setup
On Windows 10, AgIO reads RTK position from a Kalmix SCOUT over USB serial, routes NTRIP corrections back through the same port, and AgOpenGPS reports RTK Fix under open sky. Heading, roll, vehicle control and safety are separate system-level tasks and are not covered here.
How AgOpenGPS gets its position
AgOpenGPS is a free, open-source guidance and section-control application for farm machinery, run on a Windows tablet in the cab. The receiver connection is handled by AgIO, the companion service that opens the GNSS serial port, connects to the NTRIP caster, and hands position to AgOpenGPS. The official AgIO orientation covers that split in more detail.
AgOpenGPS takes position from a receiver that outputs standard NMEA 0183 on a serial port AgIO can open. In this tested setup that is a Kalmix SCOUT over USB-C at 115,200 bps, with no interface board in between.
This guide covers the path shown above. Everything downstream of it is out of scope.
Before you start
What you need
- A Kalmix SCOUT PRO or SCOUT GNSS receiver. The integrated USB-C cable carries both power and data, so no separate GNSS board or USB serial adapter is required.
- A Windows computer or tablet. A USB-C adapter may be needed if the host has no USB-C port.
- AgOpenGPS and AgIO from the official release page.
- An NTRIP account: caster address, port, mount point, username and password.
- An internet connection for AgIO to reach the caster.
- An outdoor spot with a clear view of the sky for Stage 3.
Connect the RTK receiver and read NMEA in AgIO
The goal here is narrow: Windows sees the receiver as a serial device, and AgIO can read its output. A valid position is not required yet.
Connect the receiver over USB-C
Plug the receiver directly into the Windows host.
Find the COM port in Windows
AgIO asks for a COM number, and Windows can assign a different one after the receiver moves to another port. Open Device Manager and expand Ports (COM & LPT). In this example Windows lists the receiver as USB-SERIAL CH340 (COM9). If several entries look plausible, unplug the receiver and watch which one disappears.
Open the GPS port in AgIO
In AgIO's Connect GPS window, set GPS to the COM port from Device Manager and the baud rate to 115200, then connect. Kalmix receivers output standard NMEA 0183 at 115,200 bps by default.
Leave the separate RTCM port empty. That field exists for setups that send corrections out on a different port; on this path corrections travel back through the same GPS port.
The receiver icon turns green and the byte counter beside it keeps moving. The position stays invalid indoors, which is expected.
One serial port, one application
Only one program can hold the port at a time. Close Kalmix TRACE, a serial terminal or any other GNSS utility before connecting the same port in AgIO.
Route NTRIP corrections through AgIO
The NTRIP account, the correction path and the GGA interval are typed once and stored in a profile.
Enter the caster details on the Source tab
This is where AgIO learns which correction stream to subscribe to. Open NTRIP Client Settings and match your provider's details to the labels on the Source tab:
- Enter Broadcaster URL or IP — the caster hostname or IP address.
- Caster Port — the port your service specifies. AgIO shows 2101 as the default.
- Username and Password — the credentials exactly as issued.
- Get Source Table — retrieves the available streams once the address and credentials are in.
- Mount — the stream for your region and service. This is the NTRIP mount point.
- Verify URL or IP — checks that AgIO can reach the address.
The Host and IP values at the top identify your own Windows machine, not the caster.
Get Source Table returns a list of mount points. Nothing back means the address, port or credentials are wrong.
For what caster, mount point, GGA and RTCM actually mean, see Inside NTRIP: how RTK corrections reach the rover.
Choose the correction path on the Position tab
This tab decides how corrections reach the receiver and what the caster is told about your location. On the Position tab:
- Select Use GPS Fix so AgIO reports the receiver's own position to the caster. Networked services that pick a nearby or virtual base need this.
- Under Send To GPS Using, turn SERIAL on so it shows green, and turn UDP off so it shows red. AgIO enables both by default; UDP is for setups where an AgOpenGPS board receives the corrections over the network instead of a COM port.
- Set GGA Interval (secs) to whatever your provider asks for. This example uses 20; entering 0 disables it.
SERIAL green and UDP red.
Leave the Advanced tab alone
The Advanced tab holds connection-protocol options: an HTTP version selector, an Only TCP:Port button and UDP Send Packet Burst. All three stay at their defaults here. Remember the HTTP selector though: if a caster refuses the connection while the Source tab details are demonstrably correct, this is the tab to revisit.
Save the setup as a profile
Open Profiles and create a profile or use Save As. The example below saves it as ntrip_config; a name that identifies the receiver and the correction service will be easier to recognise later. Profiles keep the whole communications setup, RTK settings included.
Reopen the profile once before leaving the desk and check that the COM port, baud rate, caster, mount point, GGA interval and Serial output survived. A profile stores settings, not sessions, so NTRIP still has to be switched on outdoors. The profile name appears in the AgIO title bar once it is loaded.
Confirm RTK Fix in AgOpenGPS
Configuration is done. This is where the receiver, the correction stream and AgOpenGPS have to agree.
Put the receiver under a clear sky
Move the whole setup outdoors and place the receiver antenna-up with a broad view of the sky, away from walls, roof edges, vehicles and large metal surfaces.
Start AgOpenGPS and confirm a position
Reconnect the receiver and launch AgOpenGPS.exe; AgIO starts with it and loads the saved profile. Check the COM number against Device Manager first. If Windows assigned a new one, change only the port and leave the baud rate and NTRIP settings as tested. Wait for Lat and Lon in AgIO to change from 0.0000000 to real coordinates: the byte counter alone only proves the cable is alive.
Turn NTRIP on and watch corrections leave AgIO
Press NTRIP On. The status moves through authorisation to Listening and the downloaded volume starts climbing, which shows AgIO reaching the caster.
Whether the corrections get to the receiver is a separate question, answered on the receiver icon. AgIO shows the data bytes sent and received on that port; the sent value reads as dashes until corrections start flowing. When it turns into a byte count, AgIO is writing RTCM into the serial port.
The sent-byte value beside the receiver icon changes from dashes to a number, and the NTRIP status reads Listening.
Confirm RTK Fix in System Data
Give the receiver time to track satellites and process the incoming corrections. Click the GGA icon in AgIO to open System Data, which lists solution quality, correction age, satellite count, HDOP and the live NMEA sentences.
The AgOpenGPS status line reads RTK fix and System Data reports Quality: RTK fix with a low correction age.
What this guide does not cover
The positioning path is complete: the receiver is read, corrections are delivered, and AgOpenGPS shows RTK Fix. Nothing above that layer was configured. Heading and roll, the steering controller, the wheel-angle sensor and the actuator were all left out, and nothing was run on a moving machine. Those belong to a vehicle-integration guide.
Positioning accuracy is a separate question, measured under controlled conditions and reported through Ground Truth rather than in a setup guide.
Troubleshooting the connection path
Faults fall into two groups, and it pays to separate them before changing settings. If AgIO cannot read the receiver, nothing about corrections matters yet.
The receiver link
| Problem | What to check |
|---|---|
| No COM port appears | Reseat the USB-C cable, try another host port, and check whether an adapter is required. Watch Device Manager while reconnecting: the entry should appear and disappear with the cable. |
| AgIO cannot open the GPS port | Something else is holding it. Close TRACE, a serial terminal, or any other GNSS utility, then reopen AgIO. Only one application can own a serial port. |
| The port opens but no bytes arrive | Check the baud rate before anything else. Kalmix receivers output at 115,200 bps; a mismatched rate produces an open port with no readable data. |
| Bytes arrive but the position stays at 0.0000000 | Expected indoors. The serial link is working and the receiver simply has no fix yet. Move outdoors with a clear sky view before judging anything about GNSS or RTK. |
| The saved profile has the wrong COM port outdoors | Windows may have reassigned the number after reconnection. Change the port only, and leave the tested baud rate and NTRIP settings alone. |
| AgIO has position but AgOpenGPS shows none | AgIO hands position to AgOpenGPS over UDP on the local machine. Check that both are running, and that a firewall or security tool is not blocking loopback traffic. |
The correction path
| Problem | What to check |
|---|---|
| Get Source Table returns nothing | Work outwards: internet connection, caster address, caster port, credentials, then account status. If all of those are demonstrably right, try a different HTTP version on the Advanced tab, because some casters are strict about it. |
| NTRIP authorises, then disconnects | Many services allow one session per account. Close any other client using the same credentials, including a phone app left running in a pocket. |
| NTRIP is Listening but the receiver stays Single or Float | Corrections are reaching AgIO, not necessarily the receiver. Confirm the sent-byte value beside the receiver icon has changed from dashes to a number, that SERIAL is on and UDP off, and that the GGA interval matches what the service expects. Then check that the mount point suits your location. |
| A VRS or nearest-base service never sends corrections | These services need to know where you are. Confirm Use GPS Fix is selected, that the receiver already has a position, and that the GGA interval is not set to 0, which turns the report off entirely. |
| RTK Fix appears, then drops | Watch the correction age first: a rising age points at the link, not the sky. Then check the internet connection, the caster stream, nearby obstructions and whether the USB connection is stable. |
Frequently Asked Questions
Can AgOpenGPS use a Kalmix SCOUT as an external RTK receiver?
Yes. AgIO opens the receiver as a USB serial device at 115,200 bps, reads its NMEA 0183 output and passes position to AgOpenGPS, with no interface board in between. Tested on Windows 10 with AgOpenGPS 6.8.5 and AgIO v1.0.0.
Does this guide prove that autosteer works?
No. It covers the position input layer: serial NMEA, NTRIP corrections delivered over the same port, and RTK Fix visible in AgOpenGPS. Autosteer additionally needs heading and roll, a steering controller, a wheel-angle sensor, an actuator, control tuning and a safe field test. None of that is covered here.
Should I use the Serial or the UDP correction path?
Serial, when the receiver plugs into the Windows machine and shows up as a COM port. UDP is for setups where an AgOpenGPS board carries the receiver and an IMU and reaches the tablet over the network.
NTRIP is connected but RTK Fix does not appear. What should I check?
Check that the sent-byte value beside the receiver icon has changed from dashes to a number, that SERIAL is on and UDP off, that the GGA interval matches the provider's requirement, and that the receiver has a genuinely open sky view.
Next: decide what the machine needs
Receivers used in this test
Kalmix SCOUT PRO
L1/L5 RTK receiver for field and machine deployment. Verified here over USB serial at 115,200 bps.
View SCOUT PRO →
Kalmix SCOUT
Entry-level L1/L5 RTK receiver. Verified here over USB serial at 115,200 bps.
View SCOUT →Other field setups are grouped by industry on the Integrations hub. Working through a setup that does not match this one? Tell us what you are building and we will point you at the right path.