A 559Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE
In a sea of seemingly sameness among GPS receivers, it can at times be difficult to wade through and find much of a reason to be excited over newly announced RTK devices. Humanity has managed to bridge the technological hurdle of putting all of the necessary components for RTK in a single, cable-free housing, and has done so with aplomb. Welcome to the 21st Century…(where’s my flying car?)
Technological hurdles aside, one barricade that has remained frustratingly unhurdled is an economic one. Prices for high-tech RTK gear have indeed declined steadily over the past decade, while the cost of a low-tech cup of coffee seems to have curiously sky-rocketed. Even with the prevailing economic winds blowing quite favorably for consumers of GPS equipment, the ever elusive $20,000 barrier for a dual frequency RTK system harkens to Captain Ahab’s obsessive search for Moby Dick.
Once upon a time, buyers with a $20k budget would find themselves looking in the used department or perhaps in the "scratch and dent" bins (as those thriftiest among us will relate). Well, prospective buyers can prepare to "ease the sheet" a little as this price point is now on the horizon. (Where are all of these seafaring metaphors coming from?) Champion Instruments is marketing a fully equipped system for a list price of $19,995.
Any time a deal seems "too good to be true", we’ve all been conditioned by advice or class time at HKU (Hard Knock University) to exercise extra caution. "What am I giving up in quality or features in buying this product at this price point?" I eyed the Champion TKO Base + Rover system with the same wary eye and found myself overall very pleased with what I saw, both empirically through testing and subjectively through use.
First, what does a relative new-comer like Champion know about GPS? How can this start-up possibly have better technology than a big corporation with a long history of development and large research and development budgets? The short answer is that they probably can’t. The longer answer is that they don’t need to. The components that make up the TKO receivers are name-brand, such as the Pac Crest OEM receiver boards and UHF radio modems. Champion didn’t bother to reinvent the wheel.
The result is a very mature system that is rich in features and capability and yet is more accessible with its lower price tag. Just some quick specs to make the point:
The 220 channel receiver is able to track GPS (L1, L2E, L2C and L5), Glonass (L1, L1P, L2 and L2P), SBAS, and Galileo (as an upgrade). It can employ corrections from CMR, CMR+, CMRx, RTCM 2 and RTCM 3. It can output up to 50 Hz in a wide range of ASCII formats and in Trimble’s binary GSOF. The included radios are 2 watt UHF radios at 430-450 MHz or 450-470 MHz and can be boosted by an external antenna kit. The CPU is an ARM9 processor with 64 MB of internal memory for storing static files for post-processing.
Physically the system weighs a shade less than 4 pounds (somewhat of an industry norm) and is powered by a single 7.4 volt Lithium-Ion battery. It has two physical ports. One port does double duty as a RS-232 com port and external power, the other does the same with the added ability to function as a USB port. It also has an internal Bluetooth port for wireless connectivity to the data collector. The face plate employs three buttons and three status LED’s. The underside of the TKO also has a speaker for providing the receiver’s status audibly. (I’d be okay with exchanging the heavily accented Asian voice with that of Elizabeth Hurley or James Earl Jones). Internally there is a SIM card slot for GSM (which at present is not functional) and a built-in communication module port for installing a radio modem.
Champion serves their customers well by supplying the user with a very complete package of accessories including the two receivers, with the UHF transceivers (allowing each receiver to operate as a base or rover), base tripod and tribrach, carbon fiber rover rod, four batteries, two bay wall charger, two hard shell cases, data collector with software, data collector bracket, UHF booster with external antenna and UHF extendable tripod. The consumer is fully equipped to collect data and precisely navigate to points in the field.
And while the TKO’s internal GSM ports do not function, the included Scepter data collector does include a functional GSM port that allows users to connect to real time networks. Expect to see the Scepter data collector become a common platform for data collection. It’s inexpensive, constructed well and multifunctional. It’s operated by Windows Mobile 6.1 with a 624 MHz processor and includes 256 MB of internal memory. If that isn’t enough it also accepts micro SD cards. Internal GPS allows the user to navigate within a couple of meters to points in the field, the internal Wi-Fi gets the user online access (perhaps while enjoying that aforementioned overpriced cup of coffee), the SIM card slot allows it to function as a smart phone or a connection to internet based GPS corrections. Just don’t anticipate using it cabled up with your old total station. Serial connections are limited to Bluetooth, but isn’t everything these days? And you can take 3 megapixel pictures with its built-in digital camera and access it fast with its dedicated camera button. Batteries are field replaceable important to anyone who has to work a full day further than arm’s reach of a power outlet. Recharging is done via the USB port (which makes it possible to recharge almost anywhere).
Field Use
Even in the thick woods of East Texas, we found ourselves exploiting the TKO system frequently. The system choked under the dense pine trees (as every RTK system I’ve ever used has), but did well beneath moderately obstructed skies. Tracking Glonass improved chances of getting a fix in tough areas, at times tracking 17-18 satellites! I’m finding that even though much of our area is RTK hostile, I don’t have to go far to find a suitable place to observe a point under friendlier skies. Several times we were able to take the TKO with us as we located remote boundary monuments. We simply observed points in the open and measured to the enveloped points conventionally with no traverse required. I could easily see such a compact system all but entirely removing the need for conventional traverse, and making it possible to collect points with only a single trip, dramatically reducing time in the field.
I found the system’s statistical analysis extremely dependable. Fixed solutions were reliable. The range was generous with the internal radios. Over hills and through creek bottoms with thousands of feet of trees between, I could routinely exceed a mile of baseline length. The battery life was passable. Perhaps the batteries I was supplied were beginning to wear a little but I usually experienced about 5½ hours of use before needing to change them instead of the advertised 8 hours.
The internal 64 MB of memory is ample for the purpose. I stored a static file recorded (inadvertently) at a one second per epoch interval–which is excessive for a long OPUS solution. The session was 3 hours and 41 minutes and created a 12.2 MB file. Extrapolating from this, I could have logged a 19 hour file, collecting GPS and Glonass at one second intervals. Multiply those 19 hours by 10, 30 or 60 (more practical epoch rates) and you begin to get a better picture of the realistic memory potential.
Downloading the static file was simple. Using the USB port, the receiver behaved as any external thumb dri
ve or memory card, allowing simple copy/paste downloads with no special software. The static file was in a proprietary ZHD format which had to be converted to RINEX before submitting to OPUS. For in-house post-processing you might be on your own regarding software as Champion currently does not appear to offer commercial processing software with their system.
Precision
As you, dear reader, have come to expect, I performed a short baseline test to determine the repeatability of the system. Before laboring with the details of the test, there are a few things I’d like to mention. First, I’m not NGS and this isn’t nearly as rigid as one might expect from such an agency. Second, this test is fairly easy to conduct with a data collector and spreadsheet software. I would encourage anyone with RTK or testing RTK to do this to become better acquainted with the real-world capabilities of their current or potential RTK system.
I placed the receivers approximately thirty feet apart and set the data collector to log a point on one minute intervals using the auto collect feature. Each minute the data collector dutifully logged a point while the rover remained static. Once complete, I downloaded the data collector and created an ASCII file of the points–Northing, Easting and Elevation. I then imported this data into Excel for study. I averaged all of the coordinates together to determine the "true" position of the receiver. I then subtracted the results of each point from the overall average and was shocked by the results. The TKO outperformed many far more expensive systems. Horizontally, only 23 of 319 observations exceeded one centimeter (7%). Vertically, only 82 of 319 observations exceeded one centimeter (26%). From the stored observations, I found a standard error of less than 0.02 foot horizontally and 0.03 foot vertically.
This was borne out in the field as well. For conventional control points, I would typically observe each point for 3 minutes before occupying with the total station. Each time I would check the horizontal and vertical distance between the two points I would establish for conventional ties, I was surprised to find the components consistently checked within this standard error.
Overall Impressions
The TKO Base + Rover system easily keeps pace with the big boys and does so at a significant cost savings. This makes sense. The TKO is one of the big boys at heart. The internals are reputable, the accessories are ample, the capabilities are impressive, and the precision is commendable. Holding the system in hand, I do get a sense that the housing might suffer damage under extreme abuse. The thin plastic cover doesn’t inspire as much confidence as other receivers I’ve held. It seems plenty durable for field use in the conditions and environments we often find ourselves in, but they likely won’t tolerate a lot of abuse, but then I don’t make a habit of abusing $20k investments. Do you?
I would like to see support for postprocessing, but in practice, I would likely never use it, except in extremely rare instances (perhaps making a case for a web-based cloud processing option). Considering the comparisons between this system and other, more expensive systems, I would more likely take the $5k (or more) price difference between the TKO system and the other competing systems all the way to the bank. Or, in our credit driven culture, keep from making payments on that extra $5k (with interest) all the way to the bank.
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 559Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE