Lateral Crown Offset Method

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TOPIC: Back to Don Bertolette
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== 1 of 1 ==
Date: Sat, Jan 12 2008 1:40 pm
From: dbhguru@comcast.net

Don,

For the benefit of those who may have trouble visualizing the measurement challenges we've been discussing, I am including a short table below that shows 12 examples of the magnitude of the height measurement error attributable to use of an incorrect baseline with the tangent method. If the baseline error is small and the angle is small, the error is correspondingly small. However, an error of 20 feet in the baseline combined with a high angle to the crown point and presto, the error skyrockets.

The biggest reason most users of clinometers and hypsometers are likely to repeatedly make baseline errors is due to their understandably following the instructions that are provided with clinometers and hypsometers. A forester with a good eye for the differing crown architecture of trees and possessing of excellent depth perception can partially compensate for the baseline error. Of course, there is little or no baseline error when measuring the height component from eye level to the base of the tree.

Bob

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TOPIC: Sample Problem
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== 1 of 3 ==
Date: Sun, Jan 13 2008 2:01 pm
From: dbhguru@comcast.net

ENTS,

What follows is a thought exercise hopefully to make more concrete the challenges associated with relying on a clinometer and baseline to measure tree height. I've put te exercise together for those of you with the necessary interest, but who feel shaky around the calculations. Please feel free to criticize this sample problem, call for more, or whatever. At the least, I would anticipate that Ed, Will, and Lee can think of some further clarifying points.

Suppose a measurer with clinometer and tape measure sets out to measure the height of a tree under the following assumptions.

a. The measurer sets a107.5-foot baseline from eye to a level point at the perimeter of the tree and then adds two feet to approximate the center of the trunk. That is, the measurer decides to take the tree's radius into account, which is calculated as 2 feet. So the arrived at baseline distance to be used is 109.5 feet.

b. The high point of the crown is observed to lie directly to the left of the vertical centerline from the ground up through the trunk. Let's assume that the horizontal distance between a plumb line from crown-point to ground and the center line of the trunk is 13.3 feet (this is unknown to the measurer).

c. Unknown to the measurer, the measurer's clinometer reads high by a quarter of a degree

d. From the selected vantage point, the measurer reads an angle of 39.25 degrees to the high point, which remember, is to the left of the trunk centerline. However, the measurer treats the baseline as the 109.5 feet from eye to the center of the trunk.

e. The ground in the vicinity of the tree is assumed to be level so that a final height determination requires adding then measurer's height to eye level. This will be ignored in the calculations below.

Having set the baseline, the measurer computes the part of the tree's height that is above eye level through the following calculation:

H = tan(39.25)*109.5 = 89.5 feet.

How close is the measurer to accurately computing the above eye level component of height? The actual horizontal line from the measurer's eye to the intersection with the vertical line upward from the ground and through the crown-point is given by:

D = SQRT(109.5^2+13.3^2) = 119.8 feet

Taking into consideration that the clinometer reading is high by 0.25 degrees, the tree's actual height above eye level can be calculated as:

H = tan(39.25-0.25)*119.8 = 97.0 feet

Of course, the measurer is unaware of the error, but the difference between 89.5 and 97.0 feet is not insignificant. From the measurer's chosen vantage point, the measurer has understated the tree's height above eye level by 7.5 feet. Shouldn't the measurer have been aware of the risks?

This scenario is but one of many possible to consider. Had the measurer lined up eye, crown-point, and trunk in the same vertical plane and still established a baseline to the trunk of 109.5 feet, the actual height of the crown-point above the measurer's original vantage point would, of course, not change, but the calculated height would. The measurer would be positioned at a horizontal distance of 109.5-13.3 = 96.2 feet from the vertical line from ground to crown-point. From this second observation point, the measurer would record an angle that we can calculate using the inverse or arctangent function.

Degrees = atan(97.0/96.2) + 0.25 = 45.5 degrees.

Using this angle, from the second vantage point, the measurer would calculate the tree's height above eye level as:

H = tan(45.5)*109.5 = 111.4.

This represents an over-statement of the tree's actual height above the measurer's eye level vantage point of 14.4 feet. I emphasize that we are assuming level ground only for simplicity's sake. Computing the below eye level height component seldom presents problems. So, using the same length of baselines and taking the angles to the same crown-point from two different locations, we see a swing in calculated height of the crown-point above eye level of 21.9 feet. One measurer could have recorded a difference 21.9 feet removed from another.

From the second vantage point, had the measurer set up a baseline of exactly 100 feet to the center of the trunk, the angle that would have been read would have been 48.2 + 0.25 or 48.45 degrees. Remember, in this scenario, eye, crown-point, and trunk are in the same vertical plane. From these assumptions, the measurer would calculate the tree's height as:

H = tan(48.45)*100 = 112.9 feet,

which compared to the actual height of 97.0 feet gives a difference of 15.9 feet. The 0.25-degree error in the clinometer calibration accounts for about a foot of measurement difference in these calculations. The overwhelming portion of the measurement error in these calculations results from the measurer not properly locating the crown-point being measured relative to the measurer's location.

One may argue that an experienced measurer will always line up the eye, crown-point, and trunk so at least, they all lie in the same vertical plane. In this case, the measurement error would have come from the second vantage point(s) and been either 14.4 or 15.9 feet in the over category, attributable to the erroneous length of the baseline, i.e. 109.5 in the first case and 100 feet in the second as opposed to 13.3 feet shorter in both cases.

An especially interesting scenario is the following. Let's assume a configuration of measurer and tree that forms the following triangle as laid out in a horizontal plane. First, we extend a level line that spans the distance from the eye to the center point of the trunk, then straight outward to intersect the plumb line that extends from the crown-point to the ground, and finally, from that point of intersection back to the eye. The base of this triangle is the 13.3-foot crown-point offset distance. One leg of the triangle is the 109.5 feet. If we assume the crown-point is positioned so that the other leg of the triangle is also 109.5 feet, we get an isosceles triangle. The measurer accidentally gets the right height above eye level except for the clinometer error.

I find the last scenario especially compelling. It illustrates how errors can compensate to provide an accidentally accurate result even though the measurement methodology is fatally flawed. Alternatively, a skilled user of the clinometer and baseline method may have developed methods to compensate for the crown-point offset distance. I would put Don Bertolette, Russ Richardson, and other experienced foresters in this class. Before the days of lasers, Lee, Will, and I fit that mold. But standing from afar, short of continuing discussions, it is by no means clear who out there is skilled at compensating and plenty aren't. In fact, discussions that I have had with clinometer only users indicate that most are unaware of the magnitude of the risks of the technique or how to go about assessing the risks. Unless one possesses the skill to visualize and construct the mathematical models and reveal sources and probable magnitudes of error range due to both one's instruments and mathematical models, one is left with little more than faith - in which case, one points, shoots, and reads a result from a scale.

Bob

== 2 of 3 ==
Date: Sun, Jan 13 2008 4:21 pm
From: DON BERTOLETTE

Bob-
Of course, the Leverett School of Precise Dendromorphometry will have a distinct advantage, especially if tree height measurement runs from 1/2 to 6 hours per tree.

A forester is seldom tasked with precise height measurement. We are taught to see a tree in 16' log segments (or multiples of four for some applications), and then only to a merchantable top. This varies with the species and region, but would be specified in a timber sale contract or crew assignment. And we'd be expected to measure many trees in a day, typically with a random check where more accurate and complete measurement is undertaken.
As foresters, we were thought to have diminished capabilities, so technicians would be issued standard rules of thumb, such as the following:
1)Using clinometer with percent scale, go out 33.3, 50, or 100 feet or until your measurement to the top is less than or equal to 100%. 50 feet in second cut eastern hardwoods was often enough to be far enough out to measure tops.
2)Walk around enough to get a feel for the relationship between top at first look, and when you have a good view of what you think is the top, then walk to where the top/bottom displacement is in a vertical plane perpendicular to the line between you and the tree.
3)Recheck 50' distance to perceived pith, then take reading. Say that you read -8% to bottom of tree, and +40% to top of tree, with an accurate clinometer. Multiply the distance by 2 (had you been at 100' you'd have read direct, at 33.3', mulitply by 3). Again, because foresters run a lot of numbers through their head, it's best to keep it simple. In this instance, the tree measured would be approximately 96' tall.

Vertical displacement off of true is inconsequential when measured with the displacement constrained spatially in a plane perpendicular to line between tree and forester.

Judgement as to what is the highest twig is critical for the LSOPD, for a forester, judgement comes into play in assigning the highest merchantible diameter meeting a four foot log segment length. Deciduous trees have proportionately smaller amount of their height that is merchantable. Conifers have proportionately more. Judgements on mercantible tops in very tall stands are more difficult and stress precision needs, particularly in NW.As forest technicians, our equipment was fairly simple...D-tape, rag tape for distance, clinometer, plumb bob (for working out where vertical is), and a paint gun to identify which trees have been measured/numbered.

As I review above comments, I'm thinking many will object to the efforts foresters take to expedite the process, that we should commune with tree and establish some kind of rapport with the forest. Ask Mike, Joe, Russ, or other foresters if they have much margin to play around with. LSOPD folks don't have a particular dollar bottom line or time constraint for what a forester might call a 'high dollar' tree (candidate old-growth or champion tree), and definitely would have a hard time doing an inventory of all trees in a 60 acre stand.

It's two different tasks requiring different strategies, tactics, equipment, time, and purposes.

More than enough for now, I'm sure...sorry to have rambled!
-Don

== 3 of 3 ==
Date: Sun, Jan 13 2008 6:38 pm
From: dbhguru@comcast.net

Don,

I have no quarrel with methods used in forestry for the intended forestry purposes. I've tried to make that clear. My example on this list is meant for ENTS tree measurers who want to attain reasonable accuracy, but who get confused by input from other sources, especially the coordinators of the state champion tree programs who push forestry methods. If we're serious about our numbers in ENTS, we should go for the better techniques, unless of course, they are simply too complicated for most tree measurers to use. However, I would argue that the ENTS sine method is not even complicated, let alone too complicated, unless the measurer is unwilling to do any calculations at all.

In terms of effort, with the TruPulse 200 or 360, designed with foresters in mind, I can measure the height of a tree to a degree of accuracy commensurate with range of accuracy built into clinometer (within half a degree) and laser rangefinder (under half a foot) within a few seconds - half a minute tops. Don't know where the 1/2 hour to 6 hours comes from except if you're are referring to my taking lots of measurements in order to get the error down to no more than a couple of inches on a very special tree or just joshing the rest of you about my tree measuring compulsion.

It is important to note that with either of my TruPulses, I can flip between the sine-based VD mode and the built in tangent-based height algorithm. With the latter, I immediately introduce an error that averages between 8 and 11 feet. So, why not use the more accurate method when the measuring time is about the same? That has been my question to Laser Technologies. Haven't gotten a satisfactory response back yet. The reason? There is no satisfactory response.

I'm unsure of what you meant in the statement "Vertical displacement off of true is inconsequential when measured with the displacement constrained spatially in a plane perpendicular to line between tree and forester". Can you elucidate? If you measure horizontal distance to the plumb line from the crown-point and the angle to the crown point, you're going to be as accurate as the accuracy of your baseline and clinometer allow. If there is no error in either, then you'll be dead on.

Bob

== 1 of 5 ==
Date: Sun, Jan 13 2008 8:40 pm
From: DON BERTOLETTE

Bob-
I agree...

With regard to last point, if I view a conifer tree and find its vertical displacement is to the north, then I'd measure its height from either the east or the west. I don't need to know how far it is displaced to the north, as I'm not measuring the length of the tree, but the height. I'd take a clinometer reading to the base, and a reading to the top...I realize that with short baseline distances, this would introduce some amount of error (I don't have a concise way of explaining this other than to say that it would be the difference between a chord and a circle that one would describe swinging a 360 degree circle...not a significant error with a hundred foot baseline I think).
-Don

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TOPIC: Sample Problem
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== 1 of 4 ==
Date: Mon, Jan 14 2008 6:40 am
From: dbhguru@comcast.net

Don,

Field foresters are to be congratulated for using the offsetting technique. I'm certainly not questioning your experience in the use of the technique or the degree to whic you observed it used, but in walking the woods with a dozen and a half foresters over the years measuring trees, I think one or two may have consciously employed that method. Others clearly did not. Some suggested taking several readings and averaging them. Others aligned eye with trunk and crown point. So there is some confusion about the degree to which the procedure is followed. It may be that the Forest Service ran a tighter ship. And, the procedure you describe is not demonstrated in the instructions accompanying clinometers. To the contrary, they suggest alignment of eye, crown point, and trunk. Although your method is clearly superior, I suspect the extra time needed to identify maximum lateral displacement is viewed as a time determent - certainly if done for every tree.

The impact on height of the adjustment of the baseline to a point lateral to the trunk is easily calculated. It requires nothing more than the use of the Pathagorean Theorem. As an example, suppose the baseline is 100 feet to the trunk and the crown point is laterally 30 feet to the side. Then the horizontal distance from the eye to a plumb line from crown point to ground is:

SQRT(100^2+30^2)= 104.4 feet. At a 45 degree angle, this would introduce 4.4 feet of height error by using the baseline to the trunk. At a 30 degree angle the error is 2.5 feet, and at a 60 degree angle, the error is 7.6 feet.

On a 125-foot baseline, a 45 degree angle, and a 35-foot lateral crown displacement, the error would be 10 feet. Even this is not an overwhelming error. So, the magnitude of the errors being made using clinometers that we see cropping up time and again in champion tree lists would suggest that the majority of clinometer users don't use the method you describe. Rather, I think they most often misidentify the top as a forward thrusting, upturned limb combined with an arbitrarily long baseline taken all the way to the trunk.

BTW, I made some silly arithmetic errors in my sample problem that nobody (obviously me) caught. Today, I will rework the example to illustrate the correct numbers and place the potential sources of error in better context.

Bob

== 2 of 4 ==
Date: Mon, Jan 14 2008 5:43 pm
From: DON BERTOLETTE

Bob-
While it's been a few decades since I was active as a certified timber marker, our training included such things as what you refer to as an offsetting technique.
As much walking around as is needed to measure each tree, one soon learns techniques to cut down on 'time' spent walking...if I were able to create an isoceles triangle by walking from one of two trees that I had just measured dbh on, to a point equidistant (walk out one leg pulling distance to a point equidistant to other tree, I'd measure heights (presuming, here for example, that they were both plumb) of both. We usually would go out in three or four person crews, one of whom tallied the calls...after a year or two of doing this, with the same guys, you could keep up to three or four trees data (species, dbh, height) to call out at once, more efficiently using the tallier. Three good callers could really make one tallier hurt, even in the steep terrain of SE Kentucky. To keep everybody honest, the tallier had a random number generated that would select a tree for 100% tally (done by someone other than the original tallier). I'd guess that for every 1000 trees we'd measure, 100 trees might get a 100% tally, and 1 of those trees would get a mill tally, where we actually would go to the mill that the timber sale trees went to, and compare our tally with what the mill actually was able to cut...this involved both physical dimensions (length to commercial top limit, number of logs, as well as our grading of that quantity (accounting for wounds, out of round shape, knots, fungus/rots, butt swell, etc.).
It wasn't just the vision of a Friendly's sherbet, or a tall chimney glass with condensation dripping down the sides of an ice cold adult beverage, that would allow me a sprint out of the woods after a long day hunting old-growth!
-Don

== 3 of 4 ==
Date: Mon, Jan 14 2008 5:53 pm
From: ForestRuss@aol.com

Don:

You aren't talking about the old "3 P" sampling the FS was trying out in the
early 70s are you?

We marked a lot of timber like that on FS sales in Montana with a crew setup
just like you described. I still have my certificate as a "certified
cruiser" so I could be one of the measurers. We used poles, binoculars and
relaskops and the accuracy standards we had to aim for were intense.

Russ

== 4 of 4 ==
Date: Mon, Jan 14 2008 8:29 pm
From: DON BERTOLETTE

Russ-
I had done the 3P elsewhere, but yeah, despite the view from outsiders, USFS does know how to inventory forested lands...
-Don

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== 1 of 3 ==
Date: Mon, Jan 14 2008 2:59 pm
From: dbhguru@comcast.net

ENTS,

The attached spreadsheet allows one to calculate the error in height from following the strategy of aligning oneself so that the top being measured is laterally to the left or right of the trunk, i.e. at a 90 degree angle. It is a good strategy, but let's see if we can calculate the error associated with different measurement scenarios. In the spreadsheet, Columns A,B,C and E are for input. The other columns are calculated and have been protected to prevent accidental overwriting. I have put numbers in the input columns to show as examples, but they can be over-typed. The horizontal offset angle is how much the measurer misses in aligning the crown point at 90 degrees to the vertical plane that includes the eye and base of trunk. Angles in the direction of the measurer are entered into the spreadsheet as positives, thus reducing the angle to less than 90 degrees. When the crown point lies behind the perpendicular line, the angle is entered as a negative. The formula needed for
the error calculation is in cell #1.

As can be seen in my sample data, the largest error is 10.34 feet, which is based on a 45 degree angle, a 67-foot line to the trunk, and a horizontal offset angle of -15 degrees, meaning that a level line from eye to trunnk and then to the point of intersection with the plumb line from the crown point is 105 degrees. Elevate the vertical angle from eye to crown point to 60 degrees and the measurememt error jumps to 17.9 feet. I will acknowledge that some of these scenarios may be judged unlikely for an experienced measurer. Nonetheless, the error calculator serves its purpose.

Bob

 Baseline Dist to trunk lateral leg of triangle Hypotenuse angle Hgt using Base Hgt using Hyp Diff 67 5 67.19 45 67 67.19 0.19 67 10 67.74 45 67 67.74 0.74 67 15 68.66 45 67 68.66 1.66 67 20 69.92 45 67 69.92 2.92 67 25 71.51 45 67 71.51 4.51 75 5 75.17 45 75 75.17 0.17 75 10 75.66 45 75 75.66 0.66 75 15 76.49 45 75 76.49 1.49 75 20 77.62 45 75 77.62 2.62 75 25 79.06 45 75 79.06 4.06 100 5 100.12 45 100 100.12 0.12 100 10 100.50 45 100 100.50 0.50 100 15 101.12 45 100 101.12 1.12 100 20 101.98 45 100 101.98 1.98 100 25 103.08 45 100 103.08 3.08 125 5 125.10 45 125 125.10 0.10 125 10 125.40 45 125 125.40 0.40 125 15 125.90 45 125 125.90 0.90 125 20 126.59 45 125 126.59 1.59 125 25 127.48 45 125 127.48 2.48 150 5 150.08 45 150 150.08 0.08 150 10 150.33 45 150 150.33 0.33 150 15 150.75 45 150 150.75 0.75 150 20 151.33 45 150 151.33 1.33 150 25 152.07 45 150 152.07 2.07 Max Diff 4.51

 E = Tan(A) * [D - SQRT(D^2 + d^2 - 2 * D * d * Cos(90 - a) Eye level baseline dist to trunk (D) Crown-point horizontal offset. distance (d) Horizontal offset angle (a) Direct horizontal  distance to crown-point (L) Vertical angle from eye to crown point (A) Calculated tree hgt using  distance to trunk (Ht) Calculated tree hgt using actual horizontal distance to crown point (Hh) Tree height measurement error (E) 67 5 15 65.88 25.00 31.24 30.72 -0.52 67 10 5 66.87 30.00 38.68 38.61 -0.07 67 15 0 68.66 35.00 46.91 48.08 1.16 67 20 -5 71.57 40.00 56.22 60.06 3.84 67 25 -15 77.34 45.00 67.00 77.34 10.34 75 5 15 73.86 45.00 75.00 73.86 -1.14 75 10 5 74.79 45.00 75.00 74.79 -0.21 75 15 0 76.49 45.00 75.00 76.49 1.49 75 20 -5 79.29 45.00 75.00 79.29 4.29 75 25 -15 84.97 45.00 75.00 84.97 9.97 100 5 15 98.82 45.00 100.00 98.82 -1.18 100 10 5 99.63 45.00 100.00 99.63 -0.37 100 15 0 101.12 45.00 100.00 101.12 1.12 100 20 -5 103.68 45.00 100.00 103.68 3.68 100 25 -15 109.17 45.00 100.00 109.17 9.17 125 5 15 123.80 45.00 125.00 123.80 -1.20 125 10 5 124.53 45.00 125.00 124.53 -0.47 125 15 0 125.90 45.00 125.00 125.90 0.90 125 20 -5 128.30 45.00 125.00 128.30 3.30 125 25 -15 133.67 45.00 125.00 133.67 8.67 150 5 15 148.78 45.00 150.00 148.78 -1.22 150 10 5 149.46 45.00 150.00 149.46 -0.54 150 15 0 150.75 45.00 150.00 150.75 0.75 150 20 -5 153.05 45.00 150.00 153.05 3.05 150 25 -15 158.32 45.00 150.00 158.32 8.32 Max Diff 10.34

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TOPIC: Sample Problem
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== 1 of 3 ==
Date: Tues, Jan 15 2008 4:29 am
From: dbhguru@comcast.net

Don,

Very clear description of the length to which you all went to generate good data. I have little doubt that you all developed a very high level of expertise and that served you well. I wonder if the care that you all took in those days is still the situation today? Any thoughts?

Bob

== 2 of 3 ==
Date: Tues, Jan 15 2008 10:28 am
From: DON BERTOLETTE

Bob-
Without any doubt! Being a forest technician was kind of like Anyclass 101, designed to be a washout class...those that couldn't handle the physical rigors of the job, didn't last. Those that didn't relish time in the woods, wouldn't last. Those that couldn't handle being in the woods year around, didn't last. When I signed on at the Redbird, everybody above me, but the Ranger had been there since the Purchase Unit opened in 1964. I had gone through two changes of rangers during my time there, but the rest of the folks in the Timber side were still there. I haven't been back, but I would be surprised if all but two were still there (those two would likely have retired at the maximum age). They held a lot of esteem in the community (except for pot growing segment..;>)
-Don

== 3 of 3 ==
Date: Tues, Jan 15 2008 2:55 pm
From: dbhguru@comcast.net

Don,

It has long been my not so humble opinion that over its history, the Forest Service has built a mixed record of performance, but some of those performancies have been among the best to be seen by any government agency. Don Bragg has mentioned some absolutely superlative forests in his neck of the woods. According to Don, they are among the best managed in the world, i.e. real forests, not plantations . I would not doubt Don's assessment one bit. Then there are iconic figures like Aldo Leopold, and lesser known, but nonetheless stellar performer, William Ashe. Leopold had much to do with today's environmental ethics. So, it isn't hard for me to accept that along the way the Forest Service has developed some truly first class management programs and your experience with the Forest Service seems to have incorporated some of the topnotch programs. Unfortunately, the Forest Service gets caught in the political climate and jerked first in one direction and then the other. We can on
ly hope that this present miserable administration in Washington w ill not be replaced by another of like mind, i.e. that of the corporatist.

Back to the FS you knew. I, for one, would enjoy hearing about some of your experiences in the Forest Service and later the National Park Service. Care to pass along a few stories?

BTW, I propose to ENTS to name the lateral offset method of measuring tree height, the "Bertolette Offset Method". I realize that you didn't invent it, but nobody else has described the process on this list and once you explained how you were minimizing the measurement error, it became immediately apparent to me that the method needs wider explanation and promotion. Anyone can test the accuracy of the method for any scenario using the formula that I presented in a prior e-mail, i.e.:

E = Tan(A) * [D -SQRT(D^2 + d^2 - 2 * D * d * Cos(90 - a)]

where:

E = error in tree height from incorrect baseline distance

A = angle from eye to crown point

D = eye level distance to trunk

d = horizontal crown point offset distance (horizontal distance between the two vertical lines, one through the crown point and one through the base of the tree).

a = angle deviation of the crown offset point relative to the 90 degree angle formed going out at 90 degrees from the horizontal line from eye to trunk. Obviously the desire is for a to be zero. If a is 0 and d is 10 feet, the height error for angles in the range of 30 to 60 degrees varies from 0.29 to 0.86 feet for a baseline distance of 100 feet. For shorter baselines, the error can exceed one foot, but is unlikely to exceed two feet. For D = 67 feet, d = 20 feet, A = 60 degrees, and a = -15 degrees, E = 13.4 feet. Obviously, the measurer must be skilled and experienced.

Finally, I just got word that Laser Technology Inc. is shipping me two t-shirts with a TruPulse 360 logo as thanks for my testing of their instrument. I am evidentally a pretty big hit with them. Well, I'd rather have a bundle of cash, but nonetheless, I will wear my 360 t-shirt with pride.

Bob

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TOPIC: Sample Problem
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== 1 of 1 ==
Date: Tues, Jan 15 2008 10:04 pm
From: DON BERTOLETTE

Bob-
Hmmm, I appreciate that the naming of the method was intended to be an honor, but not even my wife took my last name! I am just one of many forest service technicians that employed the mentioned techniques and many others that we probably never thought twice about. How about naming it Q&E Offset Technique? Quick and Easy...:>)

Stories? 1975. I was a USFS party chief of a survey crew on the Deerlodge NF. I was working with a crew in the fall, outside of Boulder Montana (an hour or so north of Evel Knievel's hometown of Butte). We were tasked with putting in the P-line from the end of a USFS haul road, to open up access to a series of timber sales south and west of Boulder.

A P-line is a Preliminary line, essentially where the line drawn on paper gets transferred to the ground. We'd put in stakes that represented tangents (off of curves), then come back and gather topographical data on both sides of the P-line, take that data back into the office and compute cuts and fills for a road width of given dimension.

Midway through the survey, after having run through the woods essentially on a sidehill contour, the grade dropped a little and went through a 100 acre clearing...as we stopped and ate lunch at the edge of it, I noticed the spreading panorama before us had nary a road in sight.

Coming from California where USFS was embroiled in a Roadless Area Review process, I took it upon myself (and crew) and restaked the preliminary line to remain in the woods and connect back up with the road at the far edge of the meadow. Having done road design both in Humboldt, and in the field with the USFS in California, it was done with no significant difference to cuts and fills, or haul distances.

To make a long story short, I got called in 'on the carpet', and was directed to restake it as originally designed (had I 'bowed up', I'd have been terminated), because the landscape architect of the time, had decided that the drivers on this USFS haul road to be, needed a more diverse experience.

Yep, I'm one of those USFS bureaucrats that toe the line, spend time in the office shuffling paper and wear out desks with my boot heels...
-Don

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TOPIC: Sample Problem
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== 1 of 1 ==
Date: Wed, Jan 16 2008 6:06 pm
From: dbhguru@comcast.net

Don,

I doubted that you would go for attaching your name to the nethod. Or, how about Lateral Crown Offset Method (LCOM)? Don, I don't doubt that there are many shortcut processes that forestry has developed over the decades to simplify what would otherwise be labor or calculation intensive.

Although simple in concept, I would imagine that getting the 90 degree angle or as close to it as possible deters tree measurers in a hurry.

Bob

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TOPIC: Sample Problem
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== 1 of 1 ==
Date: Thurs, Jan 17 2008 2:53 pm
From: DON BERTOLETTE

Bob-
As a land surveyor working his way through school, one of the Q & E ways of approximating a perpendicular heading off of a line (90 degrees), was while standing on that line, to outstretch your arms left and right, aligning with known points on line. Then, with eyes closed, bring them both to front and center. Sighting down the arms/hands approximated a ninety degree angle quite well, unless you were an overdeveloped, right-armed wrestling brute. It was easy enough to determine where to take a '90' off of, having used a plumb bob to 'center the tree within itself'.
Again, these are all methods for approximation, with equipment easily at hand, and quick to employ (remember, Q&E!). Clearly your previously posted lateral offset discussion points out the extent of lateral offset error accumulates when approaching 15 to 25 feet error (per hundred foot baseline).
-Don