DataGNSS recently introduced an Android-based single frequency GNSS receiver and gave me one of their units for evaluation. It is based on the u-blox M8T and RTKLIB and appears to be aimed primarily at the surveying market. Here’s a photo of it from their website.
First of all, let me say this is the most user-friendly receiver I have worked with. From opening the box to getting a first RTK fix took less than half an hour. If it were not for a bug in the user interface that they have since fixed, I would have had it working even quicker. They have found a good balance between being easy-to-use and being configurable. Several of the user options are directly from my demo5 version of RTKLIB and it has an acknowledgment on the About screen for “Rtklibexplorer” so it looks like they are using at least a derivative of the demo5 code.
I won’t go over all the technical details, you can read the datasheet here. I also did not do any sort of extensive testing of the unit. I will just give my initial impressions of playing around with for a short time.
To get my initial RTK fix, I first needed to connect the unit to wireless and then configure it to use the NTRIP caster on my roof as base station. Both tasks were very easy and intuitive, an advantage of having a built in screen and leveraging off the Android platform. Once I had done this, I turned on the default RTK service, and had a fix in just a few minutes.
The D302-RTK can be used either with an external antenna or with an optional helix antenna. This photo from the DataGNSS website shows the helix antenna attached to the top of the unit. This can be quite convenient. Helix antennas are more omni-directional than patch antennas so are considered a good choice for handheld applications and are often used without ground planes as in this case.
The lack of a ground plane does concern me though for RTK measurements. In their antenna application notes, u-blox has some good information about the advantages and disadvantages of patch vs helix antennas including the following passage:
That said, in my limited testing I used the helix antenna exclusively and seemed to be getting reliable fixes as quickly as I usually do with patch antennas. However, I was not in an environment that would have particularly large amounts of multipath. Of course, it is also very easy to switch to using an external antenna if multipath is an issue.
The RTK solution defaults to using GPS and GLONASS but it is easy to add Galileo or Beidou. Configuring the basic settings is quite intuitive. The advanced settings are much less intuitive and unfortunately not documented. In most cases they are labelled with the same names as in RTKLIB and so can be just as cryptic.
As far as performance goes, since I believe it is using the demo5 version of RTKLIB, I would expect similar performance as you would get with any M8T receiver and the demo5 code, and my limited testing was consistent with that.
The biggest disadvantage I found was that there doesn’t appear to be an easy way to transfer solutions from the unit to a computer or other device for post-processing. I found myself taking photos of the screen to record locations. It does come with the SuperSurv application pre-loaded which will record tracks but I could not find an easy way to then download these to my computer. I imagine this is something they are working on and hopefully will improve soon. Or it may be already available in the SuperSurv app and just not obvious enough for me to find. It may also be that there is another Android app that can be downloaded to serve this purpose.
It did have a few other issues that made it feel like an early production unit which I am fairly sure is the case, presumably they will get these issues ironed out over time. In particular I found power management a problem, not when using the unit, but after you are done, it requires separate steps from different menus to stop the RTK solution and then power down the RTK module. Even after doing both, it seemed like the battery ran out quite quickly when not being used. I also experienced annoying screen flicker at times, at other times it was fine. In the first version they sent me there were also several minor menu issues which when I brought them to their attention, they fixed quite quickly and sent me a new version of firmware. My expectation is that they are working on the other issues as well and will hopefully have improvements soon.
The list price for the unit is $1199. This is a lot for a hobbyist or casual user but if it meets the needs of anyone using it in their work on a regular basis, I imagine it could be quite affordable, especially compared to other such easy to use options.
In my next post, I will describe my experience using the D302-RTK to measure an actual survey marker, something I’ve never done before.
[Update 3/17/18: DataGNSS responded to my post with a couple of updates: First of all, the SuperSurv recorded tracks are available in the SuperSurv folder on the D302-RTK and can be downloaded by connecting a USB cable between the PC and the receiver. They also suggest MapItGIS as another Android app that can be downloaded to the D302-RTK for recording tracks. Also, they have just released a new version of firmware which improves the power management during sleep mode ]