Zeiss Elta S 20 Robotic Total Station

Visiting surveying websites is one way I try to keep up to date on developments in the industry. One particular item of interest is any thread that deals with robotic total stations. I've reviewed the Geodimeter and Leica robotic total stations previously in this column. When Zeiss came out with its unit, the Elta S 20 robotic total station, I was anxious to give it a try. There has been steady improvement in this area of total stations, even to the ones already reviewed. I reasoned that Zeiss would incorporate the latest technology in its units. There was just a slight problem in getting a unit to review: it seems they are selling faster than they are being imported, and I could only have a brief demonstration and operating session with John R. Chwalibog, Zeiss's Regional Sales Manager. Some other surveyor was just as anxious as I was to have a hands-on demonstration.


The photo on page 51 shows John with basically the whole set up out in our office campus—the gun, battery, prism pole, 360º prism, RecLink control unit and, near the bottom of the pole (out of the picture), the radio link. Placing the radio link low on the prism pole helps with the balance of the pole, especially when bending down to mark a point or drive in a hub. The gun follows the 360º prism even if you lay it down to drive in a hub and tack and then pick it up again. Very little time is lost waiting for the gun to acquire lock on your position.

Battery and Data Transfer

The battery on the tripod leg is an auxiliary unit recommended for a day of continuous use. The regular on-board battery is part of the base of the unit on the left side and just forward of the PCMCIA card slot cover. Data transfer using a PC card is much faster than using the serial transfer method. The only faster method I've used is the parallel transfer of an older type of card.

The Elta S 20 has a full QWERTY keyboard with numeric keypad to allow you to work with alpha, alpha-numeric or numeric descriptors. A second full keyboard can be ordered for turning sets of angles at the gun position. The computing power is provided by a DOS 486 onboard—the same thing some of us use for our desktop computers. Zeiss has its own software but allows the option of using the popular TDS data collection software, SMI software, or MapVision software and is open-system programmable. Users of this software will be right at home with the RecLink (familiar to us as the Husky unit) the minute they type in TDS to start the program.

It's a sturdy-looking gun that weighs 8.7 kilograms fully loaded. Setup was quick and easy, thanks to the electronic leveling system that can be accessed from anywhere in the program by using the ctrl-L keys. One of the biggest impediments to productivity is having to key through menus to re-level and re-backsight the gun when it goes out of level. When I asked John how to set the PPMs, he replied, "You don't." My negative reaction turned to one of sincere enthusiasm when he explained that the gun has automatic temperature and pressure sensors that automatically make the corrections for you. Do PPMs matter? You bet they do. With this gun, I do not have to worry about it any more. Even better, if all your crews are so equipped, you do not need to remind them to do it either. It just gets done for you.

Upgrade Path

Zeiss has planned well with this series of instruments. There is a 4-step upgrade path. You can start with the "point," similar to the usual total station, except for the servo-driven horizontal and vertical motions. From there you can go all the way to remote-controlled, fully robotic operation. There is also a similar upgradable software path. The S 10 is a 1", 1mm+ 2ppm gun. The S 20, reviewed here, is a 3", 2mm+2ppm gun. Both are dual-axis compensated and will, under average conditions, shoot 2,500 meters to a single prism, 3,500 meters to a triple and 300 meters to 50 millimeters of foil. They both come with "PositionLight," a construction setting out aid. "SearchLight" is an optional aid in helping the rod position find the instrument.

One question that has gnawed at me since first seeing fully robotic total stations is how good they would be at turning sets of angles. My former professor for surveying at the community college I attended has done some informal testing to evaluate the opinions he has heard from friends of his who use robotics in their day-to-day operation. The informal results are that they are better than the human eye, turning tighter sets every time.

Electronic Instrument Person

A comment I have seen on Web pages regarding robotics concerns the loss of lock on the prism from various causes. Zeiss has evidently been reading these, too. The Elta S series uses a system termed "QuickLock." It uses a radio-transmitted serial number, unique to each radio, to signal the instrument where to turn. It has a range of 1,200 feet. Waiting for a "search" routine after losing lock has been almost eliminated. QuickLock gets you in the ball park. Zeiss calls this feature the "electronic instrument person." FineLock gets you on home plate. In the precise mode it is accurate within one second at a range of 3,200 feet. You have to punch the serial number in when starting your field work. The unit can even handle two rods.

Time constraints dictated that John, familiar with the equipment, "hop the rod." So off we went! We proceeded as if we were obtaining topo of our parking lot, but with a twist. I deliberately chose the back lot with a line of trees between it and the gun. The unit tracked us flawlessly, even when we laid the rod down, carefully, to demonstrate its ability to maintain prism lock. The interruptions provided by the trees did not interfere at all. John then ran quickly in one direction and turned 180º to force it to lose lock. It did, momentarily. A few seconds later it was right back with us.

We walked to the upper lot to a point where I could just barely see the gun through a gazebo and heavy vegetation. We also changed our walking speed and combined with the dense vegetation to force it to lose lock. I suppose we could have just shut off the radio link. "This time it will take a while," I thought to myself. It found us within a few seconds again. It was certainly an impressive confirmation of the technology of the radio link, not to mention the Elta S series.

Construction stakeout is an area where this technology can be very beneficial. You can enter the angle yourself or have the gun call it up from memory. Those who set angles on verniers or optical instruments will appreciate the digital instruments. Still, fine tuning a coarse motion took time. With this gun you just watch it turn to the angle, go out on line, take a shot (it will turn off-line to get the prism and then return to the proper angle setting), view the distance to the point and go the appropriate distance. Pound in your hub, take a check distance, set your tack, recheck if you desire, then record the point. It will give you the set point coordinates and the cut or fill information to write on the guard stake or lath. As much as I dislike the mud or dust extremes of the construction site, this gun would make it a lot more tolerable. You can set the rod aside while marking a point, pick it up and be on your way to the next point, and all this from the prism pole.

On-the-Ground Topography

On-the-ground topography is another strength. I prefer to be at the prism pole when I am the one who will do the TIN and DTM. It gives me more security to pick up the detail I know will be needed for the site at hand. I suppose it comes from too many return trips to answer the "it just doesn't look right" question. Robotic total stations make this approach feasible. A recent case drove this point home, so to speak. One of our divisions does a lot of aerial photogrammetric coal pile volumes. At one of the distant sites, a surveyor at that locale did the job with a robotic gun faster and cheaper than we could, and without a helper.

John was "quietly confident" of this gun, and it was easy to understand why after this demonstration. Don't just take my word for it: get a demonstration on one of your projects. Do a financial projection and see if it might not be time to make the change. The Zeiss Elta S guns will make you think about it.

Al Pepling practices surveying in Pittsburgh, Pennsylvania, and is the New Products Editor for the magazine.

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