Educational Material on Tangent Method

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dbhguru
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Educational Material on Tangent Method

Post by dbhguru » Wed Jun 03, 2015 7:22 pm

NTS,

One function of the AF National Cadre is to be able to explain the pros and cons of each measurement method and the conditions where each works best or worst. The big problem with the Tangent Method is the crown to base horizontal offset distance. We know how to minimize its adverse impact, and we know the positioning of trunk, crown and measurer for which the impact on height error is maximized. The attached Excel spreadsheet shows how to evaluate the minimum and maximum impact of crown offset on height error for a specified tree height, crown offset, and horizontal distance to the trunk. The spreadsheet allows one to play what-if games for different combinations of the three inputs.

Bob
Attachments
TanErrorAtVaryingDist.xlsx
(85.79 KiB) Downloaded 46 times
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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Larry Tucei
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Re: Educational Material on Tangent Method

Post by Larry Tucei » Thu Jun 04, 2015 10:54 am

Hi Bob- Perhaps Cadre members could all receive some type of Pamphlet with the two different methods in a condensed version to familiarize ourselves with comparisons of the two methods. This would show their differences and similarities and would be extremely helpful for us and future Cadre members. I hope I’m not being lazy I just have never used the tangent method. https://www.google.com/search?hl=en&q=s ... =0CBIQBSgA Found this on the Internet showing alot of NTS formulas. Larry

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Don
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Re: Educational Material on Tangent Method

Post by Don » Thu Jun 04, 2015 1:40 pm

Larry-
I'm a bit of a math-phobe, having done poorly in high school and early college advanced algebra, geometry, and trigonometry. It was years before I got through the struggling phase...I still struggle some, but for the applications I need them for, I've managed to make enough sense of them to get the job done.
When I was a forest technician on the Daniel Boone NF, and measuring trees, I found myself favoring sidehill measuring locations (no level ground on the Redbird District!). There were a lot of reasons for that, most becoming apparent after thinking about it alot...getting wildly different heights from downhill measurements as compared to uphill measurements, I found that it didn't matter which sidehill location I measured from, my measurements were close. So I routinely started measuring most trees 90 degrees (perpendicular) to their lean.

In retrospect, working for an agency that was interested in log LENGTH, I probably unknowingly skewed some of their statistics during the five years I was there. It wasn't until the 1990's when I started collaborating with Bob (on old-growth locations in Massachusetts) that I began to realize that I'd been a Tangent Method measurer most of my career. Now in my case, most of that career took place in the West, where forests were predominantly coniferous, and the vertical displacement is less of an issue.

It wasn't until I began thinking of height as the vertical distance between to horizontal planes as the true measure of height, when those horizontal planes cut through the tip top and mid-slope base of the tree. No matter how vertical the tree, or how much lean it had.

The rest of this story is trig...has to do with the sine-sine formula and what for foresters was until the 1990's the missing link...the ability to get an accurate reading of the slope distance to the tree's top. Laser rangefinders, then was the province of the military, hunters, and golfers eager to know how far they hit the ball. For us foresters, tree measuring geeks, lasers opened up a whole new world.

It wasn't until I realized that with the Sine Method, I didn't ever need to measure the horizontal distance to the trunk (a must, using the Tangent Method). Just the slope distances (and angles) to the tree's top, and the tree's bottom. The tree's middle could be doing radical gyrations like a hula hooper and it just didn't matter. That moment was an epiphany for me, and the light came on. I've been a Sine Method advocate since then...sure Bob can conjure up a few instances in which the Tangent Method will yield good results, but none of those cases can't be solved as well, or as easy, as with the Sine Method (well, barring bottom or top not being visible from one point).

Last comment after a rather long ramble...tell us how you measured trees in the past, I'd be surprised if you'd NOT used the Tangent Method all along when measuring height (includes the "Stick Method").

Re Cadre members getting a pamphlet, I was thinking that the right place for such an explanation would be on an official American Forests Cadre T-shirt... ; ~ }
Don Bertolette - President/Moderator, WNTS BBS
Restoration Forester (Retired)
Science Center
Grand Canyon National Park

BJCP Apprentice Beer Judge

View my Alaska Big Tree List Webpage at:
http://www.akbigtreelist.org

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Matt Markworth
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Re: Educational Material on Tangent Method

Post by Matt Markworth » Thu Jun 04, 2015 1:51 pm

Larry,

Good idea! I think that a simplified brochure comparing sine and tangent would be a great thing to give to the landowner, in the case when our measurement differs greatly from the original measurement.

Matt

Joe

Re: Educational Material on Tangent Method

Post by Joe » Thu Jun 04, 2015 2:00 pm

Bob and others, is the American Forests Champion Trees Tree Measuring Guidelines available online? That seems to be the definite document on the subject. I'm not sure how I happen to have a copy of that PDF file- there must have been a discussion on it in this forum in the past year. It's a masterpiece.
Joe

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dbhguru
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Re: Educational Material on Tangent Method

Post by dbhguru » Thu Jun 04, 2015 3:20 pm

Joe,

Thanks for the compliment, and yes, you can access the document at:

http://www.americanforests.org/wp-conte ... nes_LR.pdf

You probably downloaded it from the above URL. You can get to in a few clicks going directly to http://www.americanforests.org and working your way to the guidlines.

We'll be adding more material on measuring multi-stem trees in the fall. We'll also have lots of Excel spreadsheets to do the involved calculations for folks who would otherwise not want to undertake the measurement or analysis. I've attached a copy of an example of the analysis that measurers can do using an Excel spreadsheet. It is one of the many
what-if
scenario spreadsheet. It is admittedly an unusual approach to the main source of error for the Tangent Methods, but we find that we need to shine a spotlight into all the dark corners of tree measuring. Conventional approaches always show ideal measuring situations for the equipment being offered. None show a measurer what to do when the form of the tree is complicated and doesn't conform to their diagram, which in the case of champion trees is most of them.

In the attachment, I explain the scenario being addressed. However, I expect that it needs to be further elucidated with diagrams and then a longer explanation of why the spreadsheet is being offered in the first place.

Bob
Attachments
TangentPositionProblems.xlsx
(403.41 KiB) Downloaded 39 times
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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Larry Tucei
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Re: Educational Material on Tangent Method

Post by Larry Tucei » Thu Jun 04, 2015 4:34 pm

Bob- Thanks for the link on AF to your outstanding measurement guideline. The is the first that time I've seen it in the completed format. Larry

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dbhguru
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Re: Educational Material on Tangent Method

Post by dbhguru » Thu Jun 04, 2015 5:11 pm

Larry,

This is just the beginning. We'll continuously be adding to the guidelines and offering computational routines for many of the methods. We'll also look for ways to simplify the measuring protocols. There is no set time table and we don't want to rush things. As soon as AF gets our list serve set up for Cadre members, we'll be able to more effectively communicate with each other. We've considered different vehicles for communicating. A couple of folks have even suggested Facebook, but AF quickly turned thumbs down on that one for understandable reasons.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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Larry Tucei
Posts: 2014
Joined: Tue Mar 09, 2010 10:44 am

Re: Educational Material on Tangent Method

Post by Larry Tucei » Fri Jun 05, 2015 7:39 am

Bob- I understand why they wouldn't want Facebook to much Drama!!! Email is the way to go and a phone call now and then would be good. It's nice to hear a voice in the age of electronical communication. Perhaps we could have a gathering or two when all is said and done. Somewhere centrally located for everyone to attend. Larry

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dbhguru
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Re: Educational Material on Tangent Method

Post by dbhguru » Sun Jun 07, 2015 9:16 pm

Larry,

Yes, too much drama, trivia, chatter, irrelevant material, etc., and not enough control over the information. Facebook is not meant for such specialized purposes as we have in mind. We will eventually get what we need from AF but in the interim, we'll have to use regular email.

Are you ready for Durango?

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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