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Reticle Testing

PostPosted: Mon Oct 23, 2017 3:41 pm
by dbhguru
Hi Ents,

   I don't post much about tree measuring methodology on the BBS these days since it is the interest of the very few. Still, the BBS remains a legitimate repository of measuring methods. The role of the reticle-based monocular has a bright future in the American Forests champion tree program and in NTS. Accordingly, the attached Excel worksheet shows the results of the first of many tests to distinguish the theoretical from the practical. Which methods can be successfully used in the field?

Bob

Re: Reticle Testing

PostPosted: Tue Oct 24, 2017 1:34 pm
by Larry Tucei
Hi Bob-  When I get up to New England for a visit with you, hopefully this spring or next fall, this is one of the things I want to learn more about.  So in the future I can do some volume measurements of a few of the largest Live Oaks.

Re: Reticle Testing

PostPosted: Tue Oct 24, 2017 4:09 pm
by dbhguru
Larry,

  I look forward to your visit. We'll do some detailed modeling of some of the bigger pines.

Bob

Re: Reticle Testing

PostPosted: Sun Feb 11, 2018 1:58 pm
by dbhguru
Ents,

 Part of my monthly routine is to perform tests on the calibration of my equipment and to put our tree measuring processes through their paces. I frequently tout the accuracy of the reticle-based monocular. So while it was raining outside, I set up a simple test in my basement. The target was a yardstick with each foot marked off. Measuring the middle foot was the objective. Distances to the ends of the 1-foot section were 21.120 and 21.172 feet as measured with a Bosch GLM80. The reticle reading was 48. This yielded a calculated target width of 1.0160 feet. The 0.016 feet equals 0.192 inches (approximately a fifth of an inch). I'll gladly take these results.

Bob

Reticle Testing with some attendant history

PostPosted: Mon Feb 12, 2018 12:32 pm
by dbhguru
Ents,

  (This is an edited version of an earlier post.)

 Part of my monthly routine is to perform tests on the calibration of my equipment and to put our tree measuring processes through their paces. I frequently tout the accuracy of the reticle-based monocular. So while it was raining outside, I set up a simple test in my basement. The target was a yardstick with each foot marked off. Measuring the middle foot was the objective. Distances to the ends of the 1-foot section were 21.120 and 21.172 feet as measured with a Bosch GLM80. The reticle reading was 48. This yielded a calculated target width of 1.0160 feet. The 0.016 feet equals 0.192 inches (approximately a fifth of an inch). I'll gladly take these results.

  A second test measured an 18-inch ruler positioned slightly over 23 feet away. The error in the second case was 0.0131 feet or 0.1570 inches. Really, folks, we can expect to get any better than this? But the reasons we can achieve this remarkable level of accuracy include: (1) exact distances, and (2) the high performance of the reticle. This said, these tests are all conducted under highly controlled conditions. For example, visibility is never a problem.

  For more distant and less distinct targets, we can expect some loss in accuracy, but so far the level is holding to between 0.25 and 0.5 inches. I would never have expected to achieve such results with any of our instruments when we started measuring trees using laser rangefinders and clinometers back in 1996. As John Wayne might have said staring at any one of us,"You've come along way, Pilgrim."

  Along with better instruments, we have better methods. We now take into consideration factors that we hoped would be averaged out. The formula that does the work in the above tests is

Formula.png


  It is what I named the TrapezoidDiagonal-2 formula. The width to be measured is treated as the diagonal of an isoceles trapezoid. Distances to the ends of the diagonal are L1 and L2. M1 is the reticle reading, which sees the apparent width line as though it were 90-degrees to the line of sight. The formula looks intimidating and probably causes many to shy away. So we usually supply an Excel calculator worksheet that calls for the inputs to be entered into green cells and returns the result in a beige cell(s). The user does not have to evaluate the underlying formula or formulas with a calculator. It's automatic.

  My friend Don Bertolette and I collaborate on the design of these Excel calculators. Don's preference is to hide the formulas and their development processes from users as much as possible, and I'm forced to admit that he is right if our intention is gain wide acceptance for these Excel-automated methods. However, we'd like your input on what you'd like to see in the worksheets. For instance, we could present the calculator part up front without any formulas shown - just a diagram and input and answer cells. The calculator could then be followed by the developmental material for those who want to see how a method works. The question to answer is whether or not you think the latter is even necessary for the popular version. I still think it is up to some point in the initial stages. Here are my reasons why.

  In 1996 when Will Blozan and I began using laser rangefinders and clinometers to measure tree height, I put my mathematician hat on and devised formulas to make use of the fact that we could shoot distances directly to a target (top or base of tree). The Sine Method was born in name. Unknown to me, Bob Van Pelt and Michael Taylor were also using the method, but probably without giving much thought to promoting it publicly. I'm sure that the method simply made sense to them, so they used it. It wasn't rocket science. Apparently, though, I had the biggest mouth of the trio and began promoting it in NNTS, giving names to it and its rival the Tangent Method. The rest is history.

  But in those days, the Sine Method had not caught on beyond a tiny group. The standard for measuring tree height was still tape and clinometer and since it was taught in the forestry schools and used by the forestry profession, acceptance of the new method was predictably going to be a slow process. If people were going to understand where a method worked and where it failed, or at least was problematic, diagrams were needed and mathematical arguments rendered. The forum used was NTS, or ENTS in those days. More methods were developed and an analytical framework for evaluating the sensitivity of each new method to changes in input variables.  

  While from a computational standpoint, the Sine Method was no more involved than the Tangent Method, it became clear to me that getting people to put aside their institutional and professional experience and think along new lines was no small task. If I proposed a new method, shouldn't I lay the mathematical arguments on the table for all to examine and accept or reject? If I made errors in the logic, others would have the opportunity to find and point them out. Actually, this strategy worked when I came to know Michael Taylor. We thought through each others mathematical arguments and diagrams to the common benefit.  

  So now, we've moved into the bold new world of LIDAR, photo measuring, reticles, and super accurate distance and angle measurers. With these instruments, we can utilize their functionality to measure dimensions that previously we would not have attempted. For example, the missing line routine of LTI's TruPulse 360 allows us to measure the linear distance between two points in space. Practically, that converts to measuring limb length. Our friend Larry Tucei in Mississippi is making great use of the feature. And so it goes.

  Over the past year, I've found myself increasingly using the term sport-based tree measuring to distinguish what we do from what is done in forestry and other professions that measure trees. We really need to make the distinction clearly and to explain to others that what works in one arena is not necessarily suited to another. This has not always been obvious. In fact, it still isn't.

   In watching the Olympics, times measured in thousands of a second are relevant. Nobody challenges the need for such accuracy. However, in sport-based tree-measuring we still see methods used that produce results that can be in error by tens of feet. Is this acceptable in in NTS or the National Cadre? Of course not. It is up to us to set the standards for sport-based tree measuring and resist efforts to accept sloppy results that make the sport something not to be taken seriously.

Bob

Re: Reticle Testing

PostPosted: Mon Feb 12, 2018 8:05 pm
by ElijahW
Bob,

I haven’t tried out your Trapezoid Diagonal formula yet, but will once I get my replacement tripod.  When I first started measuring tree heights several years ago, the ease of use of your formuli coupled with additional directions from Will Blozan and Ed Frank made the learning curve short.  Your trunk volume spreadsheets are equally intuitive.  My preference is to have the equations hidden inside the cells, but included somewhere below or to the side of the columns.  

Thanks for your work,

Elijah

Re: Reticle Testing

PostPosted: Thu Feb 15, 2018 11:56 am
by dbhguru
Elijah,

 You're very welcome. A couple days ago, Michael Taylor sent me a very gratifying email confirming his and John Montague's use of one of the reticle formulas for measuring diameter aloft on those huge redwood trunks. It's good to see that these more advanced formulas do earn their place in our toolkit. The reticle in combination with a very accurate laser rangefinder and the right mathematical process is one of our most powerful tools.

  I just ordered a Bushnell Legend Ultra HD 10x42 Monocular, Mil-Hash Reticle, 4.2mm Exit Pupil. I guess I've joined the Toy of the Month Club courtesy of Monica's patience. They have a sale on this reticled monocular at Adorama (and also Amazon) for $171.99 plus $7.25 shipping with Adorama.

  I doubt that this instrument will be much of an improvement on the very solid Vortex Solo R/T 8x36, but the extra two power has me interested. I'm starting to focus attention on more distant targets and want to be able to see them with maximum clarity. My  Valentine goody should be here in about 7 working days. I'll give everyone a full report.  

  Beyond the new monocular, I'm still thinking about the value of LTI's TruPoint 300 survey station. It's a lot of money and while the instrument's accuracy is phenomenal, it doesn't exactly meet many of our tree measuring challenges. Still thinking.

Bob

Re: Reticle Testing

PostPosted: Thu Feb 15, 2018 4:31 pm
by Don
NTS Tree Measuring Nerds-
The above salutation is not intended to exclude others not accurately described as such, but to forewarn readers that the topical interest might be limited to those saluted.
Bob's post above set me to musing about "why"...why do we strive for excellence in our measurement of trees.  I mean, as a forester for most of my life, I've probably thrown more D-tapes around trees than most, and estimated tree heights with a clinometer and tape, with the best of them.  But in retrospect, I was operating in a different context, I was measuring a stand of trees, a forest. A forest can't be measured, reasonably, with an hour a tree, across a broad landscape.
We are measuring superlative trees, those of us who consider ourselves as 'big-tree hunters' or the more focused certifying Cadre members. We are likely to be called upon to 'prove' our accuracy in measurement, perhaps by another contending nominator. As such, we should strive to use the most accurate methods, equipment reasonably available. Bob and others among us have strived to provide the best methods, the equipment that gives us the best 'bang for the buck', and provide a common focus on replicable measurement accuracy. Much like patients going to another doctor for a 'second opinion', we have provided alternate solutions as a check on simple errors. We advocate for controlled photography (containing reference objects, device to subject distances) that we've tested enough to expect excellent estimates from afar. When we can be there, but not in "reach out and touch proximity", we've advocated for the use of a reasonably priced reticled monocular, to remotely measure remarkably accurately.

Part of that is, they deserve our best, as superlative reps of what their species can be. I wouldn't say we're tireless, but we do believe that we should continue to seek out the very 'cutting edge
of what's technologically available. With a caveat, that the technology need be reasonable in cost, available to the common man. At the forefront of this we have Michael Taylor and others seeking reasonable solutions. Recently Michael commented on the high cost of electronic equipment for  'scanning' trees. His solution was reasonable...a $50 Lumix digital camera and some public domain software that is as accurate as the LiDAR scanner. The challenge here is to work towards more user friendly software, within the reach of us "common men".  Structure from Motion (for those interested, can be further investigated at: https://en.wikipedia.org/wiki/Structure_from_motion) is a simple concept but can be daunting in it's application to the newbie.

I'd like to pose an ethical question, to stimulate discussion...how does the 'trophy hunter' on safari in Africa differ from a 'big tree hunter' out to bag a champion tree?
-Don
               
                       
DSC03744 (3).jpg
                       
from Trail of 100 Giants, Sequoia National Forest, western Sierra Nevada range, California
               
               

Re: Reticle Testing

PostPosted: Thu Feb 15, 2018 5:05 pm
by dbhguru
Don,

   Good comments about our obsession. To your final question, here are my thoughts. The trophy hunter destroys the object of his/her attention. The champion tree hunter hopefully honors his/her discoveries. Careless tree hunters may do some damage by trampling the vegetation around the base of a tree, so they don't get off scott free. But beyond minor negative impacts, the tree hunter's activities can be characterized as admiring the subject and celebrating its continued existence, as opposed to destroying it.

Bob

Re: Reticle Testing

PostPosted: Fri Feb 16, 2018 12:21 am
by Don
Bob
Good points all...
Don