> For clean Markdown of any page, append .md to the page URL. > For a complete documentation index, see https://docs.stereolabs.com/llms.txt. > For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.stereolabs.com/_mcp/server. # Using GNSS with ZED Box The **GNSS module** is an optional component of the **ZED Box with Orin NX**. It provides the global position used by the ZED SDK [Global Localization](/docs/development/zed-sdk/modules/global-localization) module and, with **Real-Time Kinematic** (RTK) corrections, reaches **centimeter-level accuracy**, significantly improving upon the few-meter accuracy of standard GNSS. This makes it ideal for applications that require highly precise positioning, such as autonomous vehicles, surveying, and precision agriculture. If you are new to GNSS, read the [GNSS Overview](/docs/development/zed-sdk/modules/global-localization/gnss) first: it explains what GNSS, RTK and NTRIP are, and how to mount the antenna. ## Installation ### Antenna The GNSS module needs an antenna with a male connector to get a signal. It must be plugged into **port 5** on the side of the ZED Box. You can use the antenna we sell in our store, or any other active GNSS antenna. However, the Wi-Fi antenna that also comes with the ZED Box will not work. ### gpsd The ZED Box is shipped with [gpsd](https://gpsd.gitlab.io/gpsd/index.html) already installed, and started at boot by a cron job. The GNSS module is available as `/dev/ttyACM0`. You can test that `gpsd` is working properly with the tool installed with `gpsd`: ```bash # GNSS and satellite data in graphical interface xgps ``` ![xgps screenshot](/_fern-files/stereolabs.docs.buildwithfern.com/b5ff2e3425587e96b0bad2d0cc59514f2d3d3e9dfd8a9072f3c887fddaf02583/docs/products/embedded/zed-box-series/zed-box/images/xgps.webp) To check the raw data of the module, stream the content of its serial port: ```bash cat /dev/ttyACM0 ``` ```text $GNGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99,1*33 $GPGSV,1,1,00,0*65 $GLGSV,1,1,00,0*79 $GAGSV,1,1,00,0*74 $GBGSV,2,1,05,10,,,29,11,,,28,12,,,28,13,,,29,3*72 $GNRMC,082019.00,V,,,,,,,230623,,,N,V*1D $GNGGA,082019.00,,,,,0,00,99.99,,,,,,*7A ``` The position fields stay empty until the module gets a fix, which requires the antenna to have a clear view of the sky. If `gpsd` is missing from your ZED Box, for example after flashing a new system image, install it by following [Setting up GNSS / RTK on Linux](/docs/development/zed-sdk/modules/global-localization/gnss/setting-up-gnss-rtk). ## Enabling RTK on your GNSS module ### Using NTRIP `gpsd` can act as an [NTRIP client](/docs/development/zed-sdk/modules/global-localization/gnss#ntrip) to retrieve RTK corrections from a base station. Replace the placeholders of the command below with the caster `` and ``, the `` of a base station less than 25 km away, and the `` and `` if the caster requires them. Restart `gpsd` as an NTRIP client with: ```bash sudo pkill gpsd # Kill gpsd if it is already running gpsd -nG ntrip://:@:/ -s 115200 /dev/ttyACM0 ``` You can now run `xgps` and wait for the GNSS to get an **RTK fix**. The *ECEF pAcc* value gives the 3D position accuracy: with an RTK FIX status, it should be a few centimeters. ### Set RTK configuration at boot To connect to the base station at every boot, edit the cron job that starts `gpsd`: ```bash crontab -e ``` And replace the `gpsd` line already present with the following: ```bash @reboot sleep 10 && /usr/local/sbin/gpsd -nG ntrip://:@:/ -s 115200 /dev/ttyACM0 ``` ## PPS signal Besides the position data, the GNSS module provides a **PPS** (*Pulse Per Second*) signal, a hardware pulse emitted at the beginning of every UTC second, which can be used to synchronize the system clock with GNSS time. See [Time Synchronization with PPS](/docs/development/zed-sdk/modules/global-localization/gnss/pps-time-synchronization) to learn why and when this is useful. On the **ZED Box**, this signal is wired directly to the `PA.06` GPIO of the NVIDIA® Jetson™ module and is handled by the standard Linux `pps-gpio` driver. PPS support is enabled by default: no device tree modification and no additional driver are required. The kernel exposes the signal as `/dev/pps0`: ```bash ls /dev/pps* ``` To check that pulses are received, read the timestamp of the last pulse twice, one second apart. The counter after the `#` should increase: ```bash cat /sys/class/pps/pps0/assert ``` ```text 1758012345.000000123#42 ``` > **Note** > > The PPS signal is generated only when the GNSS module has acquired a valid fix. If no antenna is connected, or if the sky visibility is poor, no pulse is produced. To discipline the system clock with the PPS signal, follow [Synchronizing the system clock](/docs/development/zed-sdk/modules/global-localization/gnss/pps-time-synchronization#synchronizing-the-system-clock), using `/dev/ttyACM0` and `/dev/pps0` as devices. If you start `gpsd` at boot with the PPS device, move the cron job described [above](#set-rtk-configuration-at-boot) to the `root` crontab (`sudo crontab -e`), since reading the PPS device requires `root` privileges. The PPS signal is not routed to an external connector of the ZED Box, so it cannot be used to trigger external hardware directly. Synchronization is instead achieved through the **system clock**: once the clock is disciplined by PPS, every timestamp generated on the device shares the same UTC-aligned time base. #### Device tree configuration The PPS input is declared in the device tree shipped with the ZED Box: ```c pps { gpios = <&gpio TEGRA234_MAIN_GPIO(A, 6) GPIO_ACTIVE_HIGH>; compatible = "pps-gpio"; status = "okay"; }; ``` * `compatible = "pps-gpio"` binds the pin to the Linux `pps-gpio` client driver, which is what creates the `/dev/pps0` device. * `TEGRA234_MAIN_GPIO(A, 6)` is pin 6 of port A of the Jetson main GPIO controller, that is `PA.06`. * `GPIO_ACTIVE_HIGH`, with no `assert-falling-edge` property, means that the *assert* event reported by the driver is the **rising edge** of the pulse. If you build a custom kernel or a custom device tree, for example when flashing a [Real-Time Kernel](/docs/products/embedded/zed-box-series/zed-box/real-time-kernel), make sure that this node is preserved, otherwise `/dev/pps0` will not be created. ## Using GNSS in your applications Your applications read the GNSS data from `gpsd`, in Python with `gpsdclient` or in C++ with `libgpsmm`, convert it to `sl::GNSSData`, and ingest it into the ZED SDK Fusion module. See [Using GNSS Data in Your Application](/docs/development/zed-sdk/modules/global-localization/gnss/using-gnss-data) for code examples, and the [Global Localization samples on GitHub](https://github.com/stereolabs/zed-sdk/tree/master/global%20localization) for complete applications.