Product Review: X90-OPUS

A 2.417Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

The next big thing in precision GPS might not be new technological features, but rather the significant drop in the cost of investment. Thirteen years ago Dad invested $12,000 in our first three GPS receivers, the Ashtech Locus. Small, simple, capable, and affordable, these receivers were exactly what we needed to begin our journey in precision GPS surveying. In the field, these receivers required the ability to find a set-up with open sky, set up a tripod with a tribrach and push a button. It reduced the learning curve and anxiety of taking on a new technology and became a gateway to newer, more capable equipment later on. Many surveyors bought them for the same reason and those receivers remain endeared to those surveyors to this day. Over time, this market niche (price-conscious, entry-level surveyors) has been ignored to some degree, despite historic examples of popular success, such as the Locus. Enter Mark Silver of iGage Mapping Corporation and the X90-OPUS receiver.

Mark observed a need for a drop-dead simple receiver that could be used with the similarly drop-dead simple Online Positioning User Service (OPUS) from the National Geodetic Survey. With this goal in mind, the receiver Mark envisioned would require dual frequency tracking. He approached George Zhao of CHC Navigation in Shanghai, China, to develop a receiver that could be built inexpensively with quality components. The result was an integrated 24 channel, GPS only, dual frequency receiver (actually capable of tracking L1, L2 and L2C), with a large ground plane antenna, capable of simultaneously tracking 12 GPS satellites powered by a removable rechargeable battery and a stunning internal four gigabyte memory.

Mark succeeded in making the user interface very simple. In the field, pressing the "on" button is all that is required. Once the receiver begins tracking a sufficient number of satellites, it automatically begins recording. Ending a session is just as simple–turn it off. While only one button is necessary to work, a second button allows the user to end a session without turning the receiver off and begin another. Four LED lights indicate receiver status: Red = on/off, blue = number of satellites being tracked, green = serial connection, yellow = logging interval.

The receivers include two 2200 mAh batteries that are stated to last for six hours each. I found that to be entirely realistic. The receiver doesn’t allow for hot-swapping the batteries, so if you plan on occupying a point for longer than six hours, Mark has you covered by including an external power cable. A small 12 volt battery can have the receiver running for days.

The simplistic theme doesn’t end in the field, but carries over to the office receiver download and OPUS upload processes as well. Downloading works like a USB thumb drive, plug it in to your computer and it appears as another drive. Using the X90OPUS download software, the selected files are downloaded and placed in user defined project folders. The user can enter field data as the files are downloaded such as point ID (PID), description, HI, operator, and agency. Of course you are free to enter data in all, some or none of these fields.

Mark did something really great with the HI field. OPUS works with vertical offsets measured in meters from the ground point to the base of the antenna. This is great for 2 meter fixed height poles, but not so convenient for slant heights measured from the ground point to the side of the receiver. The HI field anticipates for this by allowing a user to enter a slant height in feet by adding "SF" to the measurement (S for slant and F for feet) to which the software will automatically reduce to meters measured to the base of the receiver (the antenna reference point or "ARP"). If you’re like me and can’t remember if the magic code is "SF" or "FS", it’s no problem as either will work.

The receivers are configured for 5 second recording intervals. OPUS only uses 15 second interval data for processing, so the extra data are extraneous for OPUS submissions, but may be handy for other applications. In fact, although the receivers come pre-configured to record at a five second rate, they can be set by the user to record as fast as 5 Hz. With the large internal memory and high recording rate, this could make the X90-OPUS an appropriate solution for post processed mobile applications, such as aerial photogrammetry, but is generally unnecessary for surveyors on the ground and would add no benefits in static positioning.

For several reasons, Mark wanted the X90-OPUS to be highly functional with the OPUS utility. OPUS is incredibly reliable, both in 24/7 availability (when the government isn’t shutdown) and in the quality of results. Results are returned fairly quickly and are very accurate for land survey work. That the results are coming from NGS using the CORS network, which is constantly monitored, gives a certain pedigree to the results. If a surveyor does his part in finding a suitable site, free from obstruction or multipath, and records for a suitable length of time, the likelihood of accurate results is almost guaranteed. Along with the reliability, OPUS is really easy to use: upload a GPS file, enter limited data about the observation (instrument height), enter a return email address and wait for the NGS PAGES software to do its magic.

As easy as all of that is, the X90-OPUS download utility Mark has put together makes it even easier. Once the data has been downloaded from the receiver, the user can choose to look at the data through a full set of tools from UNAVCO TEQC to see if there are any problems in the recorded data. The data can also be "Prepared for OPUS". By preparing the data for OPUS, the utility does several things in just a few seconds: creates a copy of the file with the data decimated to 15 second intervals, tests the data in TEQC to ensure it will be acceptable to OPUS, generates a RINEX observation file and navigation file and compresses the observation file in a .zip file. This means the smallest file available is generated resulting in quicker uploads and less required bandwidth (helpful if you’re sending over a cell modem and charged by the megabyte).

The utility reviews the duration of your file and tells you whether the file is more appropriate for OPUS-RS (Rapid Static) or OPUS-S (Static). Both versions of OPUS are available from the same web page but use different techniques with different requirements for file length. OPUS-RS works with files as short as 15 minutes up to two hours in length, while OPUS-S will work with files from two hours to forty-eight hours in length. Once the user selects "Submit to OPUS" the OPUS website is opened and a pop-up appears telling the user to "press CTRL-V and enter" when the choose file dialog appears. This is because the file name and location on your drive has been copied as text to the clipboard and all that is left is for user to do is paste this text in the file name on the OPUS submission page. All of the HI information and email address information is filled in automatically. From there, the user selects upload to Rapid-Static or upload to Static. Provided enough time has elapsed since the end of the session for the CORS data to be uploaded to the NGS database, results will be emailed back in a matter of minutes (or less).

This is the simple way to collect data, download the data and get a reliable position from the data, but the X90-OPUS isn’t limited to OPUS solutions. The data can also be sent to the Canadian PPP service, AUSPOS, RTX, GAPPS and others, as well as post processing in any commercial so
ftware that supports RINEX data. So if you’re looking to expand your inventory of static receivers, this one should fold right in.

In talking with Mark about the X90OPUS receiver, he is particularly excited about the approaching OPUS-Projects utility from NGS. He’s participated in the training already and has prepared an article on the topic for American Surveyor. OPUS Projects will allow users to submit multiple files and process them with one another as well as CORS sites for a true network solution. His hope is that this will suffice for most users’ post processing needs, substantially reducing the cost of entry by removing the need for expensive post processing software, should users want to process on-site vectors.

Currently there is no processing software offered with the X90-OPUS. The receiver comes in a great kit that includes a sturdy case, external power cable for long duration occupations, download cable, two batteries, dual battery charger, instruction manual and "hold a pole" tripod attachment.

I know there are many surveyors who have resisted entering the world of precision GPS. Hesitation to learn new things has kept some from doing so, particularly as they may be closer to the end of their careers than the beginning. Many, with the understanding that surveying is a business and needs to be a profitable undertaking, fail to see the financial incentive to purchasing GPS and making the investment of time to learn the technology. After all, as enjoyable as surveying is, we still have a responsibility to provide a profit for our employees, families, and bill collectors. With this in mind, the X90-OPUS begins its own new revolution – not in the features it offers (although the simplicity of the system is impressive) but in pricing. Shockingly, Mark offers this receiver for $2450. The price alone compels consideration, particularly given that a surveyor can easily tie his or her work to the National Spatial Reference System through OPUS very easily. Certainly the used market may come close to offering receivers at this price point, but given the two year warranty on the receiver, the download utility and the fact that this is factory new should tilt the table in favor of the X90. Beyond all of that, Mark is as great a dealer as they come. I’ve personally bought from him in the past and can personally attest to his knowledge and direct customer support. Even though we don’t necessarily need another GPS receiver, this one will likely be staying with us as the price is too good and the receiver too useful to pass up.

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 2.417Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE