A 1.391Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE
The Smart Antenna is a lightweight device that includes a GPS/GLONASS (GG models) or GPS-only antenna and receiver. For connectivity, it includes a wireless Bluetooth port, a LEMO port, and a clip port for attaching to the TPS1200+ Smart Station handle. It is powered by the GEB211, and in testing ran for five hours on a single battery in 70F temperatures. It has no internal user memory, requiring it to be accompanied by the RX1250 or the TPS for data storage. It also has no built-in radio for RTK.
This concept keeps the pole from becoming top heavy, particularly with the added weight of the 360 prism in a Smart Pole configuration. On the pole it makes sense. The radio (or cell phone/ SIM card receptacle) is snapped to the RX1250, centering the weight and making for a more comfortable load. It also keeps the price of the Smart Antenna low because the RTK engine is actually in the RX1250. This will also simplify upgrades to the RTK firmware.
Working in and under canopy was impressive. Under moderate pine canopy, I could not get the receiver to fix, which is good, because if the receiver isn’t certain of its fix, I don’t want to be deceived with wrong coordinates. I was, however, able to take a measurement within arms’ reach of my office wall and repeat it an hour later to within less than a centimeter. Working beside a tree line or near obstructions was not a problem.
What sort of repeatability can you expect? We ran a small test at the Stumpwater R&D Center. It wasn’t as long as I would have liked, but should have provided a fairly realistic expectation of the system.
I set the base up, a GPS1200 with GAT1204 antenna (a beautiful system itself), on one end of a 20-centimeter initialization bar and the Smart Antenna on the other end. I then set the RX1250 up on auto collect and stored shots every 60 seconds. At the end of the test I had 359 observations (and two floats from when I changed batteries in the Smart Antenna). Excluding the float solutions, I compared each stored shot to the average of all 359 observations and came up with only four points that exceeded one centimeter horizontally, the worst of which was 1.1 centimeters. In 3D, I observed only fourteen points that exceeded two centimeters, the worst of which was 3.5 centimeters.
Leica does not use RMS (root mean squared) values to estimate the positional confidence for the user, instead opting for the 2D CQ or 3D CQ value. Although I’m not exactly sure how these values are determined, I did find them to be more realistic estimates of positional uncertainty than RMS tends to be (which is usually generously optimistic).
Leica monitors the GPS initialization for added QA/QC. The secret to RTK, dual frequency or single, is that once the ambiguities are resolved, the receiver only works with the L1 signal. This is typical of all GPS receivers, not just Leica. Leica makes use of the L2 signal throughout an RTK session by repeatedly determining the ambiguities every ten seconds and warns the user if the initialization being used doesn’t match the freshly determined, "check" initialization.
The RX1250
The RX1250 is the controller and data collector for the Leica System 1200. Previously Leica used a terminal philosophy for data in which data was actually stored on the instrument or GPS receiver. The terminal simply conveyed the commands issued by the user to the instrument, and once the instrument performed the operation, it returned the response to the terminal. To do an inverse between points, you would type in the two points to inverse and the instrument would perform the inverse and then return the inverse to the terminal for you to see. This approach allowed the user to work robotically, then step behind the instrument and work directly off the keypad on the instrument without missing a beat. It also, arguably, placed the data in the safer location, on the instrument, as opposed to the controller on the pole.
Switching from TPS to GPS required removing the Compact Flash card from the TPS and placing it in the GPS receiver to continue working. The Smart Pole necessitated a change in strategy, requiring the data to be stored at the pole, which prompted the creation of the RX1250 series.
The RX1250T (or Tc in color) is operated by Microsoft Windows CE version 5. It has 62 illuminated keys on its keypad, which are reasonably spaced for gloved hands and include a full Qwerty keyboard, twelve function keys (that when shifted allow for twelve additional function keys), four directional keys, ten numeric keys, a shift, space, caps lock, decimal, negative, enter, clear entry, escape, user and program keys (the latter functioning as the "on" key). The processor is a Renesas SH4 running at 200 MHz.
The unit is powered by Leica’s GEB211 Lithium Ion battery that is accessed through a swinging door at the back of the device. Inside the battery compartment is a slot for a Compact Flash card, judiciously placed to minimize the risk of losing data due to prematurely removing the card during a write. The battery must be completely removed, insuring the unit is off, before the card can be accessed for removal.
The RX1250 was built to communicate, having an integrated 2.4 GHz radio for robotic communication with the TPS, three Bluetooth ports, a LEMO port at its lower left corner, and a "clip" port for a snap-on radio module for use in RTK configurations.
Putting it All Together
As I worked with the System 1200 in the Smart Pole configuration, using the TPS and GPS together, I had a Bluetooth connection from the RX1250 controller to the Smart Antenna rover, a 2.4 GHz radio link from the RX1250 controller to the TPS robot and a 900 MHz radio link from the clip radio affixed to the back of the RX1250 controller to the GPS1200 base station. Not once did I have to wait for communications to be established or have to make any effort to establish the links. While the RX1250 was at work making all of these connections in the background, I was able to set up the job, open a file, or perform calculations. There were no spinning hour glasses while waiting for all of these connections to sync up before I could work. It was a true joy. Leica appears to have made some real gains with the multi-tasking capability of the RX1250 in this regard, which brings me to one of two complaints I had with the entire system.
Without ever having seen the system, I anticipated that the RTK and robotics would be accessible at the same time, but I learned that the user has to toggle from TPS to GPS, or vice versa. When the user selects the TPS, the radio clipped to the back of the RX1250 turns off (to conserve power), which results in a loss of lock. On returning to the GPS, the RX1250 powers up the radio and the user must wait to regain lock. The receiver was able to fix very quickly, so it wasn’t too much of a burden, but I would like to see the system operate robotic and GPS simultaneously and report how well the independent measurements agree.
Both SmartWorx and LGO have most every tool a surveyor might need. SmartWorx has some impressive features for linework and coding, import and export of DXF files, geodetic tools including grid/ground inverse, various projections and transformation, and COGO. LGO automatically performs a least squares adjustment of all of the data from GPS, TPS and Level work, import or export DXF, ASCII, and RW5 files. Interestingly, the SmartWorx (data collection) software does not actually maintain a coordinate file. Inversing and viewing point data is done by processing the raw data on-the-fly. It sounds like this would require a great deal of time, but it is incredibly fast.
The interface was a bit difficult, although this may be due to Leica’s marketing toward "power users." If you’ve been using your data collector for a year or more, and use it fairly regularly, how often do you read the prompts and labels? Probably not very often because you already know what it says. With highly intuitive software that has only a slight learning curve, front-end time savings are realized very quickly. This is great if you are bringing in new employees every few weeks, but if you are one to hang on to trusted software for years, then all of those helpful pop-ups get to be annoying once you learn the software. Given that the System 1200 is centered around the highly technical one- or two-man show, the "power user" software seems to be a reasonable approach.
Putting all of the pieces together, the system worked well. The SmartWorx software offers a dizzying array of options for orienting the total station to GPS positions through resections and best fit transformations. Toggling, as I described before, works well, but I wouldn’t be opposed to simultaneous operation. If the SmartWorx software doesn’t suit you, Leica also offers its own label of Carlson Software’s SurvCE for the RX1250, and I am told other companies will soon be offering versions for the RX. The accessories are well thought out and considering everything that was being done on the pole, it was very neat and organized with no cables to tangle.
Leica enjoys a strong following of supporters. Having never handled their gear to any great extent, however, I never understood it until now. Using the System 1200, I can see why many surveyors have an appreciation for Leica products that goes way back to the days of Wild. This system is a tremendous step forward in the advancement of solo-surveying. Furthermore, I can easily see how a couple of highly competent professionals could use this system in tandem as wellsome days as a single Smart Pole, some days splitting off and using the RTK and robotic separately. For such a partnership, the agility of this system offers a lot of promise.
Shawn Billings is a licensed land surveyor in East Texas and works for Billings Surveying and Mapping Company, which was established in 1983 by his father, J. D. Billings. Together they perform surveys for boundary retracement, sewer and water infrastructure routes, and land development.
A 1.391Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE