A 619Kb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE
It’s nice to pick up a piece of equipment that works right out of the box. That was my experience with the Magellan Professional ProMark500 RTK system. Building on the blade technology that made the ProMark3 RTK system such a capable L1-only RTK system, the ProMark500 is a full-on GNSS receiver, able to receive both GPS and GLONASS signals. Blade technology allows the receiver to also use observables from satellite-based augmentation systems (SBAS) to determine centimeter-level positions. As for future satellite systems and signals, the ProMark500 is spec’d to receive the Galileo signal. There are currently two test satellites in orbit; the European Space Agency continues to assert that Galileo will be operational by 2013.
However, the ProMark500 really impresses with what it can do with today’s available constellation. With the 75-channel receiver, a user can collect GPS in L1 and L2 as well as GLONASS L1 and L2 and L1 carrier from SBAS, which in many regions around the earth is a constellation all to itself. Ultimately, for the end user, the ProMark500 represents a triple constellation receiver today. Further, the SBAS signals lend themselves to improved positioning over GLONASS, because the SBAS orbits are reckoned from the same model as GPS. Time is reckoned the same, and the SBAS satellites are stationary–factors that equate to fewer variables between the two systems and, in theory, more reliable positioning. (This is discussed in more detail in the sidebar accompanying the review of the ProMark3 RTK receiver in the June 2008 issue of American Surveyor, which is available for viewing online at www.amerisurv.com).
Physically, the ProMark500 does not share much in common with the ProMark3. The ProMark500 is Magellan’s first foray into a truly integrated receiver housing that contains the receiver, antenna, battery, internal radio (rover), and memory. While somewhat radical in appearance, it is more similar to current trends by competitors (placing everything except the data collector on top of the pole) than previous offerings.
In a departure from the now common flashing LEDs found on most of the other receivers on the market, the ProMark500 has only a single LED indicating the receiver is on. Otherwise, a small Organic Light Emitting Diode (OLED) screen displays all other relevant information about the receiver at a quick glance. On the main display page of the OLED screen, 13 different icons display the status of the receiverall on a single screen. To name a few: the number of satellites being received, the number of satellites being used for the position, the status of the solution (fixed, float, DGPS, autonomous or base if the unit is broadcasting as a base), a data link icon indicating corrections are being received, and the signal latency expressed in seconds. Battery strength is indicated as well with a graphic scale and a percentage, and another icon indicates if raw data is being recorded and what percentage remains free in the built-in 128 megabytes of memory. Other screens give more detail regarding memory, firmware and the receiver’s serial number and are accessible by pressing the "page" button to the right of the display. Left of the display is a button dedicated to initiating recording of raw data.
The screen was visible in bright sun, although the power saving, automatic dimming of the screen required pressing the "page" button to make the screen visible after a few seconds of inactivity.
Interestingly, together with the 128 megabytes of internal memory, the ProMark500 is also capable of having a USB memory device plugged into its USB port to store raw data. While I did not use this feature during the review, it allows the user to download data without need to hook the receiver up to the computer, and permits a wide variety of USB memory devices to be used.
For controlling the ProMark500, I used Magellan’s Mobile Mapper Cx via Bluetooth connection. The connection was very robust and the FAST Survey software on the Mobile Mapper did a great job of managing the connections. FAST Survey offers numerous options for collecting data, controlling the receiver, and COGO calculations. FAST Survey is a joint product developed in part by Carlson Software and for those familiar with SurvCE, the similarities are apparent. However, FAST offers some nice aesthetic distinctions from SurvCE, such as the satellite display screen. FAST works incredibly well as a GPS controller and data collector, making it very easy to begin a GPS survey, with options that cover most any conceivable need for getting up and running quickly. Localizations are quick, including single point, two point (for rotation only), and multiple points distributed over a project area.
FAST is also equipped with the dependable field-to-finish routines Carlson is so well known for.
I would have liked to use the Mobile Mapper in the FAST environment using the internal GPS receiver in the Mobile Mapper. This would have allowed me to do some rough mapping of gravel roads and ponds and other low precision objects or to do reconnaissance with just the lightweight handheld. It would also be nice to have a suspend feature with the Mobile Mapper Cx. As it is currently configured, turning the data collector off requires the system to be fully turned off. The unit must then be rebooted and the file be reopened once it is turned back on.
In the Field
Throughout my testing, the system performed without incident. The base requires either the use of an external UHF or spread spectrum radio or a SIM card for connecting to the Internet to transmit correction data to the rover, as well as an external power source. While I appreciate the incredible range offered by 35 watts of UHF transmitting power, a short range, cable free option at the base would be nice. My experience has been that setting up an external radio and battery with all of the associated cabling can take as much as fifteen minutes to set up properly. With an integrated base, this can be done in less than five minutes.
The rover, on the other hand, was neatly arranged on the pole with the Mobile Mapper Cx in its custom bracket, and in spite of its apparent bulk was surprisingly lightweight on the pole. Being able to use the GPS constellation, GLONASS, and SBAS translates to "bring a sack lunch" since there won’t be any stopping due to satellite availability. I have never seen a mission planning printout with so many satellites constantly available, which meant I could use the ProMark500 on my schedule and not the other way around. When it was time to work, we worked, regardless of GPS satellite availability.
Initializations were quick. The few times a reinitialization required more than a few seconds, I simply used the easily accessible "Reset RTK" tab in FAST to jump start the receiver to resolve the ambiguities, and in seconds I was ready to work again.
Battery life was somewhat short at just over three hours, but the removable batteries (which resemble modern camcorder batteries) are small and allow the user to carry spares in the field. Because the battery door opens toward the bottom, it is a little tricky to open while the rover is still mounted to the pole, even though the locking system (a screw turned a quarter turn with a coin) was easy to manipulate.
Packaging was smartly arranged. With the exception of the external base radio and battery, receivers, spare batteries, HI tapes, data collector, bracket, tribrach, etc., fit neatly in a compact clamshell case.
The unit worked excellently in all the places GPS is supposed to work and did notably well in more adverse conditions. Moderate canopy did not hinder initializing or maintaining fixed positions. Dense canopy did what dense canopy does and precluded us from being able to get a fixed position. Fixed solutions appeared to be very reliablethere were very few short duration false fixes.
The accuracy testing we conducted one evening here at the Stumpwater Research and Development Facility showed that the ProMark500 is as capable as most of the competition, with respect to accuracy, but wasn’t particularly a stand-out. Interestingly, the results were a near perfect textbook statistical distribution. Horizontally, 65% of the 258 recorded RTK positions fell within a centimeter of the overall average of the 258 points, while 93% remained under two centimeters and 98% were within 3 centimeters, with the worst being 5 centimeters from the overall average. Note these percentages correspond very closely to the 68%, 95% and 99%, one, two and three sigma normal distribution values. Vertical accuracy fared a bit better with 72% of the 258 observations falling inside of a centimeter from the overall average. Only 5% exceeded two centimeters and less than 0.5% (only one position) exceeded three centimeters, and that was only by a slim margina paltry 3.2 centimeters. This all indicates the system functions according to the manufacturer’s specifications.
In the Office
If you just paid thousands of dollars on a real-time system, why should you care about post-processing? It is important to keep in mind that there are certainly occasions in which post-processing capabilities are vital. Whether you need the added precision of a static session, your radio quit working, you exceeded the range of the radio, or you forgot the data collector at the office, post-processing can be a real job saver. Perhaps more common, you may want to accurately tie your project a reproducible coordinate system instead of the autonomous abyss, which may call for an OPUS (static or rapid static) session, or even your own determination from downloaded CORS files.
In any event, downloading and postprocessing can be done fairly easily with GNSS Solutions, very mature software with roots in the Locus Processor from the late 1990s. GNSS Solutions is highly automated with numerous options allowing novice users to get accurate positions with minimal effort and advanced users the tools to massage stubborn data sets to get the best positions possible.
The software is also able to work with the native Carlson/FAST coordinate file format, the *.CRD, as well as several others.
Magellan Professional made a significant step in the right direction with the ProMark500a triple constellation receiver that works today. They have distinguished the system with the LED status screen instead of flashing LED’s, a feature which also allows the user to work completely without a data collector or controller.
The option to use a SIM card in GSM/GPRS enables the user to work in the ever expanding real time network community with only a rover, which allows the user to go straight to work without setting up a base station.
Still, the most compelling aspect of the ProMark500 is the cutting edge technology inside the unit and the reliable operation of the unit in the field. If your preference is to buy equipment that is hassle free and works out of the box, Magellan definitely merits a close inspection.
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 619Kb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE