LTI MapStar Angle Encoder

A few years ago, in this column, I reviewed a handheld laser device that could be used to collect data for mapping and GIS. One beneficial feature of this product was that no reflector was needed. Therefore, the time required for a rod man to walk between targets was decreased. Although this device could reduce slope distances to horizontal, there was no easy way to read horizontal angles with it—thankfully that need has been addressed.
Laser Technology, Inc. now markets the MapStar System Angle Encoder. The photographs show the Impulse LR laser mounted on the Angle Encoder unit. In Figure 1, I held an HP 48GX up to it for a size comparison. The Impulse LR is shorter and just a little taller than the 48. Both the Impulse LR and the Angle Encoder are lightweight and small. The Impulse LR is powered by two standard "AA" cells, which power it for up to 20 hours. It weighs in at 1 kg or 2.2 lbs. The AE is powered by two "C" cells, which also yield up to 20 hours of use It weighs in at 1.6 kg or 3.5 lbs.

Advanced Features
The Impulse LR can shoot out to 100 M to an overhead cable or to a stake and out to 500 M to a rock face or a building. Maximum Range is 575 M to a cooperative target. The evaluation unit came with a 1.5-4 x 16 zoom scope mounted on top. The cross hairs are more similar to a rifle scope than the pattern of most theodolites. The optics are crystal clear and the focusing was scalpel sharp. Our company is renting a similar unit with the MapStar System Electronic Compass Module for some GIS data capture evaluation. This unit has a laser dot targeting that aims the unit and the intensity of the dot can be varied to suit different lighting conditions.
Regardless of the MapStar Module being used, the Impulse LR shoots distances quickly—almost instantaneously. There is an audible "chirp-chirp" that is heard before you can move your eyes to the display. The brightness or darkness of the target had seemingly no effect on the distance ranges. I popped trees with dark bark, light bark, lightly colored utility poles, darkly creosoted utility poles, redwood fences, white picket fences, any manner of building siding material, and even grass.
On a windy day, I purposely shot a target through some blowing leaves. Depending on when I pressed the distance button, I got the leaf, the target some 300 meters beyond, or an E02 code. The E02 code signifies that the target was lost during measurement. Any person who has shot an infrared EDM across a valley through foliage that was too high to trim out of the way, and watched the EDM signal strength indicator repeatedly try to get the shot will welcome the speed with which this unit provides the distance.
Slope distance reduction is handled by the Impulse LR unit and has an inclination accuracy of ±0.1 degrees. Range resolution is ±0.01meter or ±0.01 feet. This is acceptable for GIS data capture or in the field map editing and may also be a handy tool for a solo field crew to perform field blunder checks.

Handy as a Pocket on a Shirt
There are three buttons on each side of the Impulse LR that can be user-configured. Factory default is set up for right-handed use. Good news for "lefties," the hand strap can be switched to the opposite side; even better is the ability to configure the operating buttons for left-handed use. As a good friend used to say, "It's as handy as a pocket on a shirt." There are five basic measurements. Two of these, slope distance and inclination, are taken directly in the field. The HD, VD and percent of slope is calculated by the unit for display.
Have you ever had the need to measure a building height for a zoning ordinance? How about airport obstructions? The HT or height measurement of this unit can be used for these purposes. The user simply aims at the target and takes the horizontal distance, then shoots the base of the target and follows with the top of the target; by pressing the "fire" button the fourth time the object's height is displayed. The manual has some useful tips on targeting materials and methods.
Another valuable feature is the ability to set a "Gate Window" or a minimum and maximum distance range. Only those objects which fall within the range will report the distances shot to them. Cables are available from LTI to support data downloading to a notebook or data collector. Current data collection software packages are enCampo, which can be obtained on a PC card, TDS's SoloCE, and Traverse PC Handheld. According to the manual, GPS interfaces are available for the Ashtech Reliance, Trimble Pathfinder, and the CMT MC-GPS. The manual was printed in 1998, and the user can contact LTI to see what other equipment is supported.

enCampo Software
LTI's enCampo data collection and office processing software is available on floppy disk and PC card. The software runs fine on the HP48GX. This package can do quite a lot from my perusal of it and would be better served by having its own review. One salient feature of this software and hardware package that piqued my interest is the ability to traverse and shoot stockpile volumes—we will surely test this soon at Kimball!
Now, for a few details about the MapStar Angle Encoder itself. "C" cell batteries are stored in the vertical column. The tripod adapter plate is used to secure the unit to any standard tripod with a 5/8" threaded screw. If preferred, it can also be set up on a prism pole. Angle accuracy is specified at 0.1 degrees for the prism pole mount and 0.05 degrees for the tripod mount.
The brass knobs, seen in the photographs will be very familiar to the users and admirers of the open standard transits that performed the majority of the early surveying in this country. From the hands of careful practitioners a considerable amount of very accurate work was produced, much of it rivaling today's modern work. To aim the Angle Encoder, the user must loosen the coarse knob, grasp the vertical column and rotate it to the target. Once rotated, fasten the coarse motion knob and use the fine adjust knob to pinpoint the target. For inclination or vertical angles, simply grasp the yoke-mounted Impulse LR and aim it at the target. The Impulse LR is side-mounted on a clever friction stud and the amount of friction is easily field-adjustable.

Description from the Manual
So how does it work? The small hood at the top of the cylinder, which has the display, does not rotate. It measures a horizontal angle by using an optical incremental rotary encoder. As described in the manual, the components consist of:

A transparent glass disk that has a radial-spoke pattern of opaque segments around its circumference. An infrared LED light source that shines through the radial-spoke pattern.
A light sensor that processes the light shining through the spokes. As the optical disk rotates, the radial-spoke pattern chops the light from the LED into pulses. The light sensor converts these light pulses into electric signals that are counted by the microprocessor. With additional electronics to provide direction information, the microprocessor can compute relative angles turned from the initial "power-on" position.

The manual further explains the encoder index position. There are index marks scribed on the hub and bearing housing. They are used for external reference of the internal indexing pulse which occurs once a revolution. An additional benefit is recovery of the back sight on accidental or intentional power down; the unit is capable of operating from –22F to +122F. The operation is via six buttons on the sloping display panel on the portion of the device that I termed the hood. One button, a combination of buttons, or a sequence of button pressing enables the user to address the many functions available. They are easily actuated, a definite plus regarding set up stability. For a variation of the "chiclet" type buttons they are amply sized, require minimal pressure, and are well spaced. A bulls-eye level bubble simulator can be used to aid in setting the unit up level. Cables are available from LTI to integrate the Impulse LR with the Angle Encoder and a data collector or notebook computer. The operating procedures are simply and amply explained in the manual.
Joshua Clemente, from our State College Office, is renting the Compass Module equipped Impulse LR to aid in more accurately collecting GIS data than can be obtained with a mapping grade GPS receiver alone. Keeping the GPS antennae in a more open area and using the Impulse/Compass to measure offsets to the objects being collected enables tighter positions to be obtained. This is a method of gaining a better satellite geometry resulting in lower GDOPS.
Josh spent a weekend with the system, reading the manual and getting familiar with it. He opined that it was an easy read and easily understood. His experience with the communications, cables and data transfer was similar. The combination was lighter and more compact then a similar setup that he had obtained from another source. The following Monday he was out collecting data, anxious to try the Angle Encoder.

Easy Operation
This parallels my experience and perceptions. One half hour of operation was about all it took to become comfortable with the operation of the Angle Encoder system. Using the coarse motion only occasionally acquired reasonable mapping data. Getting close to the corners of structures was easier with a combination use of the coarse and fine motion knobs. Like a first computer, the user wonders how much it will be used. Later on, as more and more applications are realized for it, one wonders how he or she got along without it. This is the same perception I envision for the Impulse LR and Angle Encoder. It might just be the tool you need to expand your services.

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

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