Laser Technology Height Subroutine. The Best Way To Use It.

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M.W.Taylor
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Laser Technology Height Subroutine. The Best Way To Use It.

Post by M.W.Taylor » Sat Aug 25, 2018 9:52 pm

Many have given the Height Sub Routine on Laser Technology forestry lasers given a bad rap because it often results in inaccurate measurements. After using the it more than a few times I realized something significant.

One of the reasons for the negative press on the height subroutine is that it is being used in a way that introduces error unnecessarily.

The manual shows distance AD. Most readers do not understand what AD is. It is the cosine adjusted baseline, not a zero degree shot. If you look carefully at the diagram you'll see AD is inside the trunk and not a trunk shot at zero degrees. Even most people at Laser Technology Inc. do not understand how to use this feature. This is understandable considering how poorly it is explained in the manual.

Shot 1: locks in the horizontal component from whatever point you shoot on the tree.

Shot 2: Angle to base

Shot 3: Angle to top


For shot 1, DO NOT shoot zero degrees or the base. I repeat. DO NOT shoot the base or zero degrees.

Shot 1 should be to the top or as close to the top as possible. This locks in the correct Hd distance that shot 2 and 3 will use to calculate height by way of the tangent method. Shot 1 is the cosine of the angle * the slope distance. It Is angle adjusted.

Let me repeat this. Shot 1 is an angle adjusted horizontal distance. It is simply the cosine of the angle * slope distance. If you don't believe this, go out and see for yourself. Go into Ht-Subroutine and get shot 1 to the top. Then exit and go to Hd mode. Shoot top again. You will notice shot 1 distance to top and Hd mode shot to top is the same.

Shot 2 is just an angle measurement. No need to get a clear view of the base.

shot 3 is just an angle measurement. No need to get a clear view of the top.

After taking shots 1, 2 and 3 the fire button is pressed again to calculate the height.

The tangent (of the difference of angle 2 and 3) * the horizontal distance from shot 1

For the final tally, the tangent is being used in the calculation. But you are using the tangent on a baseline that has already been corrected for the tree's lean just as long as you hit the top first.

The height subroutine is INCREDIBLY useful for measuring trees in a cluttered environment. You can get good height estimates without even a single clear view to the top. The idea is to find a point on the trunk through the clutter as close to the top as possible just in case the tree leans for shot 1. If possible hit the top on shot 1. But that is not always possible. Just get some part of the trunk near the top.

I will provide diagram if ENTS is interested. I encourage those with Trupulse or Impulse lasers to try this.

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Don
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by Don » Sun Aug 26, 2018 1:01 pm

Michael-
Sounds like a breakthrough to me! Well done.
I am a little confused though about:
"You can get good height estimates without even a single clear view to the top."
How do you get the distance from "...a point on the trunk...as close to the top as possible...", to the absolute top? Is that a separate add? If a diagram isn't to difficult, It may be the help/vision that I need to grasp this crux (to me) issue.
Thanks!
-Don
Don Bertolette - President/Moderator, WNTS BBS
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bribroder
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by bribroder » Sun Aug 26, 2018 2:14 pm

MT, is this the diagram in the manual to which you refer?
manual_height_measurement.png
Attached is the only version of the manual I have been able to find thus far
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IMPusersmanual8thedition.2-1.pdf
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M.W.Taylor
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by M.W.Taylor » Sun Aug 26, 2018 4:19 pm

Don wrote:Michael-
Sounds like a breakthrough to me! Well done.
I am a little confused though about:
"You can get good height estimates without even a single clear view to the top."
How do you get the distance from "...a point on the trunk...as close to the top as possible...", to the absolute top? Is that a separate add? If a diagram isn't to difficult, It may be the help/vision that I need to grasp this crux (to me) issue.
Thanks!
-Don

Don, see attached diagram of you measuring Yosemite Giant. What I am aiming for on shot#1 (of the 3 shot height routine) is to find a view of the tree top as far back as possible without losing sight of the lower trunk and / or to get as close to "True Hd to top" as possible, the blue line. As you see in the diagram, shot 1a, 1b and 1c, the Hd between laser and top are inflated and will lead to an inflated measurement after getting shots 2 and 3. Shot1d and shot 1g are pretty close, shot 1e and 1f are very good. But still in the diagram you are a little close to the tree.

The angle of top (shot 3) could be higher than the actual top due to being close to tree, but it will still be a decent measurement just as long as Shot 1 and Shot 3 are to the same point because the Hd is angle adjusted. At the very worst, you'll get conservative estimates which in my book are always better than inflations. If you have no view of the top, take the edge of the crown near the top on shot 1. But strive to find the top leader through the clutter for shot 3 if possible. If there is simply no view, then use the same point for shot 1 and shot 3, with shot 2 being to the base.

Shooting mid trunk and zero degrees usually results in inflated measurement and gross inflation if the tree leans towards you. Shot 2 and shot 3 do not require a clear view of the trunk as only the angle is being taken. Since the horizontal intercept is away from the base, shot2 (angle to base) will also have a little error, but it is negligible, especially if far away.

Quite simply, by understanding the math from shot1 you'll be able to achieve better estimates, even though you may adopt your own way of doing it.
Attachments
don using the height subroutine on a familiar tree
don using the height subroutine on a familiar tree
Last edited by M.W.Taylor on Sun Aug 26, 2018 6:28 pm, edited 12 times in total.

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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by M.W.Taylor » Sun Aug 26, 2018 4:24 pm

bribroder wrote:MT, is this the diagram in the manual to which you refer?
manual_height_measurement.png
Attached is the only version of the manual I have been able to find thus far

Yes, and that is the diagram. If you shoot level to get AD you are almost certain to get an error prone measurement if the tree leans or top overhangs. But you will notice you can't hit the top from that view in the diagram so it implies you shoot at zero straight to trunk to derive AD. But AD can be derived from any shot along the trunk all the way up to the top.

With experience you will find the correct balance between hitting as far up on trunk as possible and not hitting an over hanging leader.
Last edited by M.W.Taylor on Sun Aug 26, 2018 7:13 pm, edited 1 time in total.

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dbhguru
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by dbhguru » Sun Aug 26, 2018 5:33 pm

Michael,

Good work. I've always understood this as a way of getting around most of the error from the crown to base horizontal offset for conifers with one long trunk, but never really thought to pursue the method as you have. Your description is a valuable addition to our methods.

The above said, I think the method works best on straight-trunked conifers, upright or leaning. Broad-crown hardwoods can present problems where the upper crown is a mass of limbs and the high point is at the end of a branch that is horizontally away from the lower trunk. Older hardwoods that long ago lost their apical dominance and may exhibit repeatedly broken tops present a real challenge. Still, I see value to the method even for recalcitrant hardwoods if the measurer can pick out a spot that he/she believes is close to the true top, which might not return a laser bounce.

I see your contribution as especially important to help those who are forced to treat the tree as though its top is vertically positioned over its base because they don't have a compensating strategy.

Again. Good work.

Brian,

The diagram that you show from LTI is the one that leads tree measurers to screw up more times that Carter has (or had) little liver pills (expression from the past). Basically it was added to the methods repertoire to give manual tape and clinometer measurers an equivalent process to use with the hypsometer. It imbedded a role for the trunk, leading many measurers to believe that the lower trunk (or trunk at eye level) was a crucial part of the process. Michael has ingeniously gone past their original intention, maybe rescuing the old tangent method. Being able to just shoot angles to the chosen top and base helps resolve the clutter dilemma.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by M.W.Taylor » Sun Aug 26, 2018 6:31 pm

dbhguru wrote:Michael,

Good work. I've always understood this as a way of getting around most of the error from the crown to base horizontal offset for conifers with one long trunk, but never really thought to pursue the method as you have. Your description is a valuable addition to our methods.

The above said, I think the method works best on straight-trunked conifers, upright or leaning. Broad-crown hardwoods can present problems where the upper crown is a mass of limbs and the high point is at the end of a branch that is horizontally away from the lower trunk. Older hardwoods that long ago lost their apical dominance and may exhibit repeatedly broken tops present a real challenge. Still, I see value to the method even for recalcitrant hardwoods if the measurer can pick out a spot that he/she believes is close to the true top, which might not return a laser bounce.

I see your contribution as especially important to help those who are forced to treat the tree as though its top is vertically positioned over its base because they don't have a compensating strategy.

Again. Good work.

Brian,

The diagram that you show from LTI is the one that leads tree measurers to screw up more times that Carter has (or had) little liver pills (expression from the past). Basically it was added to the methods repertoire to give manual tape and clinometer measurers an equivalent process to use with the hypsometer. It imbedded a role for the trunk, leading many measurers to believe that the lower trunk (or trunk at eye level) was a crucial part of the process. Michael has ingeniously gone past their original intention, maybe rescuing the old tangent method. Being able to just shoot angles to the chosen top and base helps resolve the clutter dilemma.

Bob
The LTI manual diagram is misleading. It implies that AD is derived from a straight shot to the trunk. But it could be to the top, or somewhere in between.

My main point here is to know that shot1 is actually angle adjusted. From there we modify the methodology to our liking, whether it be getting as far back as possible for shot 1 or trying to see the top leader through the clutter for shot 3 and getting as high up the trunk as possible for shot 1 where the Hd is set into memory.

And yes, there are some errors for shot 2 to base due to the perpendicular intercept at ground being offset from base. But overall this angle is usually low and not a big contributor to overall error. Might be a simple formula to correct for this angle offset based on shot 1 ?

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Don
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by Don » Sun Aug 26, 2018 10:59 pm

Michael-
THanks, I've got it...(it's hard to get an idea across when words get in the way!)
Great graphic!!
-Don
Don Bertolette - President/Moderator, WNTS BBS
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Science Center
Grand Canyon National Park

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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by dbhguru » Mon Aug 27, 2018 8:38 am

Michael,

Perhaps, the application can be thought of as a height-measuring method that seeks to overcome the challenge of hitting the high twig with a direct laser shot amidst clutter. As you point out, getting a lot farther back reduces the height error from the crown-to-base horizontal offset, and of course eliminates it entirely at infinity. That said, at least in dense eastern forests, the measurer seldom has the luxury of choosing a remote location in a densely populated site.

I recall a conversation a three or four years ago with the DCR chief forester when he described a recent exchange with his colleagues. They were musing over whether it made a difference in accuracy to be one chain-length back from the trunk or two when they shot their angles. They were using clinometers calibrated in surveyor chain lengths. It was difficult for me to thread the needle and intelligently discuss all the variables one needs to juggle when measuring tree height accurately. It was apparent to me that they had followed the process of using a level baseline to trunk as a key step in the height measuring process for so long that sheer repetition had come to make the step, not only valid, but indispensable.

It's just basic plane trigonometry, but let's face it, even elementary math beyond addition and subtraction is a foreign language to a sizable percentage of Americans. Unless one is in the science or engineering disciplines, the norm is to go from high school level math to maybe a college course or two and then math fades into just a lot of bad memories.

Bob
Robert T. Leverett
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Co-founder and President
Friends of Mohawk Trail State Forest
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Erik Danielsen
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Re: Laser Technology Height Subroutine. The Best Way To Use

Post by Erik Danielsen » Mon Aug 27, 2018 6:47 pm

This explanation is very helpful and makes a lot of sense. Where possible, it could even by refined by doing a little scouting in HD mode to find a viewpoint where the highest and lowest points on the trunk that can be hit with the laser are roughly the same horizontal distance from the measurer. The error expected for shot 2 could otherwise be pretty significant when dealing with steep sloping terrain and trees with odd curvy forms, as are commonly the case in any old-growth one can find over here.

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