It's been a while since I talked about my GPS/GNSS efforts. Some time ago I bought a SimpleGNSS board from Ardusimple to try out. The SimpleGNSS has the new U-blox NEO-F10T GNSS receiver. This was my first experience using a new U-blox generation 10 device. It is the first GNSS device of any kind I've used that includes features specific to the latest version 4.11 of the National Marine Electronics Association 0183 standard. And it's the first I've used that's capable of receiving the new L5 band signal from the latest Block III GPS satellites.
I was about ready to dismantle this experiment. But before I removed it from my workbench, I thought I'd update y'all on my latest version of the Hazer library and its gpstool utility.
Hazer is a Linux/GNU/C-based library that supports the processing not only of the usual NMEA 0183 output of GNSS receivers, but also proprietary binary output like UBX from U-blox devices, and CPO output from Garmin devices. It also handles input and output of RTCM messages in support of differential GNSS, yielding geolocation precision down to about a 1.5 centimeters. (I run a DGNSS fixed base and a stationary rover 24x7 at the Palatial Overclock Estate.)
gpstool is the Swiss Army Knife of Hazer. It's one of those old-school tools that has a nightmare of command line options. I use it to functionally test the library, and also as the main component of most of my GNSS efforts. You wouldn't want to use gpstool to navigate cross-country (although I have used it in conjunction with OpenStreetMap to generate a moving map display in real-time). But I find it really useful for testing and evaluating new GNSS devices and just generally futzing around with geolocation and precision timing.
(You may want to click on the short video clips to view them on YouTube instead of from this blog; the UI seems to crop the images, losing some information. You can also click on photographs to see a larger image.)
Here is a short video clip of a Raspberry Pi 4B running gpstool with the NEO-F10T connected via USB.
Besides processing the output of the U-blox device, gpstool is following the 1 Hz One Pulse Per Second (1PPS) digital output signal from the device, which is syntonized to GPS time, and strobes another digital line on the Raspberry PI, syntonized to 1PPS (subject to software latency), to which I've attached a red LED.
Here is a short screen capture that shows the output from gpstool. I've SSHed into the Raspberry Pi from my Mac desktop to run gpstool. The utility uses some simple ANSI screen controls to update the display in real-time. I'm viewing standard output directly from gpstool, but the utility also has the ability to run headless in the background as a daemon, and you can view this real-time display remotely at leisure. (This is how I run my DGNSS systems.)
If you have perused the output of gpstool in any of my prior articles, you may notice a new field in the SAT lines showing the frequency band used by the device to receive data from the indicated satellite, e.g. L1 C/A. Some GNSS devices (like this one) may receive data from the same satellite over more than one band. (I confess this "new feature" is a long delayed bug fix because I botched the handling of new fields in version 4.10 of the NMEA 0183 spec. I have no excuse.)
gpstool isn't just a passive monitor. You can use its command line options to send NMEA, UBX, and other message formats to the device to interrogate and configure it. I did this with the NEO-F10T. Here is a screen shot of a snippet of a script similar to the one I used to generate the output shown in this article. It sends a batch of UBX messages, sequentially, waiting for an acknowledgement for most of them, to configure the device.
You can find this script in its entirety in the Hazer repository on GitHub.
Finally, in addition to the standard output, gpstool generates log output on standard error, which here I capture in a file. (If you run gpstool headless, log output can also be automatically directed to the system log without any need for a command line option or API call.)
In this example, I have the log output level set to INFO (informational) and above; setting it to the DBUG (debug) level and above generates more output than I typically need unless I am actually debugging new code. (The logging system is a feature of Diminuto, my Linux/GNU/C-based systems programming library on which Hazer and gpstool are built; Diminuto has its own ginormous feature set.)
That's a quick update of some of my latest poking around with GNSS. I'm always on the lookout for new (to me, anyway) GNSS devices to play with!
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