TruPulse360 and Macroscope 45
  Aug 30, 2007 19:08 PDT 

   Unfortunately, I don't own it yet. It is only borrowed. However, by mid-September when LaserTech announces its availability, my order will be one of the first.

            On the serious side, the TruPulse 360 is a potentially very valuable instrument to us. It adds easy 3-dimensional measuring to our reparatory of methods. Imagine two points in space with no particular orientation. Add a third point representing the measurer. There is no requirement as to the location of the 3rd point with respect to the first two. The TruPulse 360 allows the measurer to determine the linear distance between the first two points. The 360 also returns the vertical distance and horizontal distance between the the points and azimuths from the observer's position.

            The two points could be the ends of a limb or the extremities of the opposite sides of a tree representing the maximum crown spread. The 360 could be used to create a 3-dimensional map of a tree. Although, the TruPulse 360 will not perform like an Impulse Laser, it is sufficiently versatile to allow us to efficiently explore 3-dimensional territory. In the next several days, I'll be testing the 360 for a limited type of ground-based canopy mapping and dutifully report the results.

            The weakness of the TruPulse is that it doesn't shoot through narrow canopy gaps. With reflectors, that might be less of a problem, but reflectors can't be put on the ends of branches 50 feet up in the air. So, additional mathematics will be necessary. Nonetheless, for us, the 360 appears to be a big addition. Unfortunately, it is expensive, costing $1,600. Were it priced at half that, it would be a steal, but $1,600 is expensive for the level of accuracy it allows for distance (within a foot), azimuth (within a degree), and vertical angle (within 0.25 degrees).

            On to another gizmo. My new Macroscope 45 is proving to be a challenge. Its reticle is scaled to 3 millimeters instead of 5 like the Macroscope 25, so one must be farther from a tree to get the same diameter coverage. The factor used to compute width is not 75, as it is with the Macroscope 25, but appears to be 45 (3/5*75?). I say appears to be. I have to get more exact measurements to know.

            At this point my advice to any of you contemplating a purchase is to stick with the Macroscope 25.

True Pulse 360
  Sep 01, 2007 07:44 PDT 

    Well, yesterday was a highly productive day for me. Monica and I went to visit a friend in Stoddard, NH, and while the ladies had a chance to renew their long friendship, I skipped out with the TruePulse 360 on my belt and a 200-foot taper measure in my hands. The day's objective was to test the horizontal angle measurer of the 360.

     The first couple of hours proved to be wasted. I got bizarre results for horizontal distances with the TruPulse and had to go through the recalibration process before the instrument settled down. The instructions for recalibrating miss a point or two, but eventually I figured out what the authors of the instructions intended to be done. After recalibration, it was all goodness and light. I did 14 carefully setup experiments to measure the horizontal, vertical, and slope distances between two points in space as measured from a third location- namely where I was at. The three points can be oriented in any fashion. So the experiments were useful to test the feasibility of making crown and limb measurements measurements.

      The results of the experiments were encouraging. The average horizontal distance from the tape measurments for the 14 separate situations was 14.1 feet. The average of the best laser measurements for teh situations was 14.4 feet. The average of the best was used because I took multiple readings and often saw patterns that indicated that I had missed the sometime indistinct targets. Also, interference from power lines, cars, etc. can throw off the internal compass readings. One, must be very conscious of one's surroundings when using the horizontal angle measurer. The average of all the instrument readings for the tests was 13.0. The difference of 1.1 feet is consistent with the expected level of accuracy for 3-dimensional calculations over a wide variety of field conditions. However, being careful or using a tripod, I think the average would have been closer, perhaps +/- 0.5 to 0.75 feet.

      The uses to which we can put the 3-dimensional capability are many. The following is a mere sample.

        1. Crown spreads (maximums and averages)
        2. Limb lengths
        3. Crown point-horizontal offsets
        4. Trunk segment lengths
        5. Trunk widths (error level may be too high)
        6. Crown volume calculations
        7. Full tree mapping (error level may be to high)
        8. Vegetative surveys where location of each tree/species is desired
        9. Location of a tree relative to an established landmark
      10. Angle of limb departure from trunk (with law of cosines)

      The biggest disadvantage of the TruPulse is that it doesn't thread the needle when there is clutter in the way. In addition, if the target is small with items around it, you can never be sure that you are hitting the most distant point. For example, if you are trying to measure the length of a limb structure, you may be okay where the limb joins the trunk, but hitting the end of the foliage section where there are multiple targets is a crap shoot. I need to do more testing to determine sensitivity.

      Well, on to the day's testing with results to be reported later. Oh, by the way, the ML (missing line routine allows you to compute the height of a tree via the sine top-sine bottom method without that being a specific intention of theirs. It gets around the limitations of their built in, tangent-based height routine.

      The TruPulse 360 is way cool.

TruPulse 360-final report
  Sep 04, 2007 09:52 PDT 

     Today the TruPulse 360 that has been loaned to me for testing goes back to its home at LaserTech. All in all, I'd say that the instrument performed well and it has many potential applications for us. I need lots more time for testing, but appreciate the opportunity I've been given. I will most likely buy a TruPulse 360, but I'm hesitant to purchase from the first run of models. If the TruPulse 360 is like the RD1000, the first models don't have all the kinks worked out.

     For quick shots of the opposite sides of tree crowns to get crown spread, or the opposite ends of a limb to get limb length, the TruPulse could be invaluable. It can even be used for some crude trunk modeling, but I would emphasize that we need to keep approximating methods distinct from more exacting methods such as what we can accomplish with the Macroscope 25/45.

     One of the tests performed on the 360 was of its relative azimuth feature - the azimuth of point #2 as measured from point #1.If the points are ground-based, you can go the the first point and shoot to the second point with a compass or the 360 to get the azimuth of point #2. If both points are in the canopy of a tree, that may not be possible. However, if both points are in the first quadrant and arranged in a configuration with the second point at a higher azimuth reading and a greater distance, then the following formula provides the relative azimuth.

     d1 = horizontal distance to point #1
     d2 = horizontal distance to point #2
     a1 = azimuth of point #1
     a2 = azimuth of point #2
     A = azimuth of point #2 from point #1

     A = 180 + a1 - arccos[(d1-d2*cos(a2-a1))/sqrt(d1^2+d2^2-2*d1*d2*cos(a2-a1))]

     There are many possible configuration of points and I'm unsure to how many the above formula applies. There will be quadrant adjustments leading to a family of formulas. All in good time. They will be incorporated into the dendromorphometry guide that some of us are working on.

     I'll soon be turning my attention to the Macroscope 45. I'm pretty confident that the better choice is the Macroscope 25, but hopefully, I'll find applications for the 45.

Testing the TruPulse 360 Horizontal Angle Measurer
  Sep 06, 2007 01:37 PDT 

     The specified accuracy for the compass built into the TruPulse 360 is listed as +/- 1 degree. That isn't too good if you want to use the 360 to measure diameters of trees. Howeevr, I think that most readings are more accurate, perhaps to +/- 0.5 degrees. To test how well the instrument works for diameter measurement, you can measure the width of of a target object with a tape measure. Then from a convenient distance, align yourself with a tree and measure the distance to each side of the tree from the reference point. Align yourself so that you are centered on the object. The distances to the edges should be equal. Now calculate the angle subtended by lines from the reference point to the edges of the target as follows.

    If    D = distance to an edge
          W = width of target
           A = angle subtended by sides of triangle from reference point to sides of target

    Then A = arccos(1 - W^2/D^2)
     Now from the reference point, take azimuth readings of each side of the target and subtract them. Compare the result to A from the above formula. You may need to repeatedly shoot the azimuth readings to be sure you are hitting the outer edges of the target.

     I didn't have time to do this when testing the 360 loaned to me.

  Sep 04, 2007 16:27 PDT 

    Gary Beluzo and I decoded the Macroscope 45 today after I made a series of comical errors. However, the final news is that the factor for the model 45 is 41.667. That corresponds to 75 for the Macroscope 25.