Accuracy of Trupulse 360 & Centurion

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mdvaden
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Accuracy of Trupulse 360 & Centurion

Post by mdvaden » Mon Dec 10, 2018 1:16 am

(Note - replies #6 .. #7 .. #14 and #15 (dbhguru .. michael taylor .. brett misfud) give the opening a head start, and decipher things)

On facebook THE TREE PROJECTS posted about measuring Centurion the Eucalyptus and getting over 100 meters height. They posted to send email for a document with their methods. I inquired about two things I can't find. Whether finger or cable trigger or remote. The other ... the height accuracy for a 360 laser. I used to use Trupulse 200 so unfamiliar with the 360. When tagging along with Atkins and Taylor it was mostly the Impulse 200LR that I learned. Can you folks who know, refresh my memory how much error potential there is for each measure of height with the Trupulse 360? If I read correctly, they did like 10 to 20 measurements around Centurion compiled to reach the height total. The fact they hand-triggered suggests accumulative error chance may be higher than they claim. Their post is at this Facebook page, and they added an email in comment people could write to access methods and photos, etc.

https://www.facebook.com/thetreeprojects/?tn-str=k*F

Thanks, Mario
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Erik Danielsen
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Re: Accuracy of Trupulse 360 & Centurion

Post by Erik Danielsen » Mon Dec 10, 2018 3:09 pm

Mario,

I just read through their field report document. I feel it was quite thorough and made great effort to provide anything necessary to be repeatable both for independent confirmation and future monitoring. It does not answer your question re: triggering methods; I'm hoping they used the free smartphone app, which I've found very effective. The rest of my comments are based on mt experience with the 200B, which lacks the 360's azimuth sensors but has a similar laser unit.

The end of the document includes some discussion of both the instrument accuracy by specs and assessment of error observed in the field by an experienced researcher, along with tripod swivel, etc. I also note they relied on VD measurements- if the software for that component is similar to the 200B, the built-in rounding and filtering in my experience returns a lower reading in most cases than seeking the most solid SD and angle figures and doing the sine geometry externally to the instrument. To my thinking, this presents the possibility of error in either direction, in particular as it relates to compiling multiple segments of vertical height. The estimated 0.4m uncertainty strikes me as realistic.

My 200LR measurements are often a bit shorter than those with my 200B, but never by more than about a foot. Nonetheless I am swayed by the arguments that there are some important error sources here that I cannot endorse being left uncontrolled for in such an important measurement and then followed up with such heavy publicity.
Last edited by Erik Danielsen on Wed Dec 12, 2018 9:02 am, edited 2 times in total.

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mdvaden
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Re: Accuracy of Trupulse 360 & Centurion

Post by mdvaden » Mon Dec 10, 2018 3:57 pm

Glad you noted what you could glean or not. Because last night, Steve from the group seemed to avoid my question. Anyhow, finally it was disclosed triggering was done by HAND ... finger pushing. It was not in the document, but replied after asking about 4 times. Their equipment lists no prism and extra tripod. This morning, I relayed to Chris Atkins what laser and method they used, and he said older precise climbing numbers make it plausible that Centurion could be 100m, but with 100% chance the new measure is uncertain. Having seen Taylor and Atkins measure over recent years using remote trigger, tripod and prism, there is a chasm between their accuracy and finger pushing. The Tree Project explanations of process compared to the standard I watched evolve the past 10 years leaves a big question mark.

In a nutshell, If Atkins had measured a single LiDAR redwood the way Centurion was just measured, I wager he would have been fired. That's the most distinct way I can explain how much better using patience, tripod, cable and better laser is. Even with photography, the difference is crystal clear between finger pushing the shutter button vs. a shutter cable. For a tree like Centurion notable enough that Sillett went there to climb, it's surprising nobody went the extra mile for the latest measure.
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Erik Danielsen
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Re: Accuracy of Trupulse 360 & Centurion

Post by Erik Danielsen » Mon Dec 10, 2018 6:02 pm

I mean, I get that the work is not up to Tayler/Atkins standards. The lack of prism usage is because they registered to different visual reference points on the trunk, which definitely does create more error room than a prism survey- but conducted carefully, not necessarily very much. Similarly with hand-triggering- larger errors will be produced by a small shake of the inclination sensor shooting at shallower angles and greater distances.

In their email to me the Tree Project guys self-identified as enthusiasts and not professionals, and given the relative paucity of job opportunities in high-accuracy tree measurement that does describe most of us here. I agree with the methodological criticisms. But I do think that it looks like they went several extra miles compared to the vast majority of amateur tree measurement efforts, and I hope they'll receive just as much encouragement from the upper echelons in continuing to improve and refine their techniques as I have.

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Re: Accuracy of Trupulse 360 & Centurion

Post by mdvaden » Mon Dec 10, 2018 7:10 pm

If a tree isn't measured accurately, its not an appropriate number to advertise to the world for a hemisphere record. Its not Atkin's standard, its more that Atkins follows a method that works. He is using something that was introduced to him. Once leaving that narrow path, climbing becomes the option to turn to. Trunk "reference" points are on curve, slanted and irregular surfaces that can appear different when aimed at from different vantage points.

I think Tsunami is a good tree to interject for a moment. The world record hemlock over 270 feet tall. I didn't announce it as tallest until after bringing Sillett to it. Tsunami broke the record by maybe 30 ft. or more, so I could safely have said it was a new record even with 20 feet of error. I could have measured like slob and still been right about the record part. But I recruited Sillett as well as Taylor. Tsunami has been so accurately measured by Atkins using a prism, laser and cable to trigger, I don't even consider new height announcements without seeking his help to remeasure. I have a prism and Impulse 200LR. But suppose I used hand triggering with no tripod and announced Tsunami breached a new height barrier like 280 feet? That would be problematic and degrading to the record keeping !!! It is counterproductive to advance a tree's height measuring to the most accurate degree, then all of a sudden lower the bar several rungs.

Not forgetting the thread OP question >> does anyone have a stat for error potential of the Trupulse 360 on a height measure? Is it accurate to a foot? To 6 inches?
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Re: Accuracy of Trupulse 360 & Centurion

Post by dbhguru » Tue Dec 11, 2018 3:44 pm

Ents in general, Mario in particular,

For those of you with an interest, the TruPulse 360 has the same laser and internal height calculation routines as does the TruPulse 200 line with the exception of the 200X. Accuracy to clear targets is slightly better than +/- 0.5 feet with the 200 and 360 lines, again with the exception of the TruPulse 200X, which has a stated accuracy of within +/- 4 cm. Most 200X's will beat this level for close targets. My particular instrument is accurate to +/- 2.5 cm, but with less precision than the Impulse 200LR. My 200LR can usually sustain +/- 1.5 cm accuracies (indebted to Michael Taylor for my instrument). On closer targets, with a tripod and trigger, accuracy is +/- 0.25 feet for the 360. If the display shows a decimal digit on the return, and the with tripod and trigger, +/- 0.25-foot level of accuracy is achieved about 90% of the time. If no decimal digits is show, accuracy is to with +/- one yard or meter.

It is fairly easy to confirm the accuracy of a particular instrument over a range of distances with sufficient testing. Most people don't do the testing, and certainly not periodically. Some people don't test at all. It is critical to do periodic testing.

Handshake alters the target that is being intercepted, and this source of error has to be controlled. Some of us learn how to minimize the impact of handshake on easy targets, but it will always lead to differences in returns, especially when factoring in weak versus strong pulses being received by a unit. The TruPulses send out a spreading elliptical signal. The dimensions of the ellipse are 3.2 inches by 2.8 at 100 feet. The rate of spread is uniform. So the ellipse would be 6.4 by 5.6 inches at 200 feet. Unless the targets within the ellipse are at substantially different distances, we usually see target distances within a foot or two. This is too much variation for world record competition.

With repeated shots and handshake, we get over-lapping ellipses. I have encountered situations where one target within an ellipse was substantially closer or more distant than another. A more distant target, perhaps representing a taller tree, might return weak a signal, and the closer, a substantially stronger one. The latter is what shows up on the display. Multiple shots might display a return from the more distant target only once in half dozen or more shots. Using a tripod and trigger can resolve such scattered returns most of the time.

The more distant a target is, the more care that has to be taken for multiple reasons - a no brainer. The bigger problem for more distant targets is more often times the tilt sensor, which has less accuracy relative to that of the laser. I've created Excel spreadsheets and posted them in the past on how to evaluate distance and angle errors over long distances for both sine and tangent methods. We have plenty of tools available to assess the sources and significance of measurement errors.

What the TruPulse 360 line offers that the 200 lines doesn't is an internal compass to support the missing line (ML) routine. This capability allows the user to measure the distance and inclination between two points in three-dimensional space. ML returns: (1) straight-line distance between points A and B, (2) vertical separation between the points, (3) horizontal separation, (4) inclination between the points, and (5) the azimuth of the second point relative to the first. The weak link here is the compass, in terms of accuracy, because of susceptibility to magnetic interference. Still, I usually get within +/- 0.5 degrees, but you have to recalibrate the 360's compass fairly often. It can be done in the field, hand-holding the 360, which gives you a warning that you need to recalibrate when you get a flashing AZ on the display.

One point that must be raised is whether or not the eucalyptus measurers used the tree-height routine of the 360? That routine implements the Tangent Method - bad news.

For some general information, ML capability is also provided by LTI's TruPoint 300, mini-surveying station, an instrument with a wide variety of routines, most of which are applicable to construction, but not so much, tree-measuring. My present role with LTI , is to evaluate the instrument's features and range of applications. At first, I thought that I had bitten off more than I could chew, but am gradually finding the strengths and weaknesses of each routine, and will eventually submit the analysis to LTI. As a general rule, the more sensors that must be brought into play, the higher susceptibility to larger errors. For example, one TruPoint routine computes the dihedral angle between to adjoining walls. This routine brings the laser, tilt sensor, and compass all into play. Where might we want to use the routine in tree-measuring? The angle between two limbs coming from a whorl at a point on the trunk might be of interest. The TruPoint can do the job.

With apologies for the above rambling, I note that the challenges of measuring the world's super tall trees located within dense forests are on a different order from what we typically experience here in the East.

Bob
Robert T. Leverett
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mdvaden
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Re: Accuracy of Trupulse 360 & Centurion

Post by mdvaden » Tue Dec 11, 2018 6:26 pm

Thank you Bob !!!! Appreciate how thorough you explain things .... A thoughtful person's post about Centurion at Facebook today, brought to mind some considerations that I will write after this quote ...
Anonymous: " ... the growth rate over a 10 year period for this tree and this species at this age would more than support the fact that the tree sits over 100m now. The margin for error can always be debated"
In the quote, I emphasized error and debate with bold and colored font. Returning from grocery shopping tonight, these realizations came to mind.

1. When lesser methods are used for measuring (finger triggering or less accurate laser) it can guarantee debate.

2. When lesser methods are used, it can guarantee uncertainty what the real height is.

3. When proper climbing is used, or the best use of prism, laser, tripods and cable, it erases debate.

In a nutshell, when Chris Atkins, Steve Sillett, Michael Taylor, Robert Van Pelt or Zane Moore measure height, there is virtually nothing to debate about error, degree of accuracy or what real height numbers really are. And that's one of the virtues about the technique they implement. They operate within a tight boundary that separates fact from speculation. Once measuring moves outside that boundary, it introduces uncertainty and boosts the debate level more.

...
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Brett Mifsud
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Re: Accuracy of Trupulse 360 & Centurion

Post by Brett Mifsud » Wed Dec 12, 2018 2:02 am

Greetings all
With regards to this latest claim for the height of Centurion, I’d love to say it is over 100m, even the 100.5m Yoav claims it is. However, I believe he’s got it wrong. Centurion was climbed and measured by tape drop in Oct 2008 at 99.6m tall (by both Tom Greenwood and Steve Sillett). In Jan 2014 it was remeasured by tape drop at 99.82m (Steve Sillett). 22cm growth in 62 months. Best case scenario from these numbers is that the tree just scrapes over 100m. Furthermore, an experienced French climber, Jeremie Thomas, did a tape drop in Oct 2016, and got only 99.67m – so it may even have lost height from the 99.82.
Yoav’s actual results give the figure of 100.9m tall (more than the 100.5m he says in the article) I suspect his hired laser (lasertech tru-pulse 360) slightly over-estimates longer hits and the 100.9m is due to the accumulation of multiple, small over-measurements, due to him measuring the tree in 3 segments: base to a fork 30m up, the fork to a blotch on the trunk about 60m up, then that blotch to the top. The laser's own specifications say +/- 20cm per measurement. As far as I'm aware, the laser was mounted on a tripod, but hand triggered.

I urged him not to publish any of these results until there was a tape drop done to confirm his height. The recent publicity will do Centurion no good as it will just encourage more people to trample over and around the tree (it currently has no boardwalk or other protective infrastructure).

To add further perspective to this measurement, we have been monitoring the growth of tall regrowth E. regnans trees (90 years old) in Victoria. For some individuals we have data for the past 14-18 years. These young, vigorous trees with pointed crowns are growing in ideal conditions in deep gullies near streams. These young trees are adding a metre of height every 4-5 years – however, due to variations in rainfall and temperature, growth does vary annually: In some years growth has been only 15cm, other years about 30cm. Let us compare this with Centurion: Here we have a flat topped 500 y/o tree growing on an exposed ridge. We know from Oct 2008 to Jan 2014 it grew only 22-23cm. That further measurement in 2016 indicated it may have lost a little in height and dropped to 99.67cm. Even if the conditions had been ideal for growth in the last 2 years since the last tape drop measurement, growth rates for an essentially flattish dome topped 500 y/o tree will still be significantly lower than those growth rates for the regrowth trees mentioned above. How likely is it that the tree grew 22cm in 5 years (2014 tape drop number) then grew 70-110cm in the next 5? Or more improbably, the tree grew 7cm in 8 years (2016 tape drop) then grew 80-120cm in 2 years? In light of this information, I strongly believe the claimed laser height needs a tape drop to confirm it.

regards
Brett
Last edited by Brett Mifsud on Wed Dec 12, 2018 2:32 pm, edited 2 times in total.

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mdvaden
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Re: Accuracy of Trupulse 360 & Centurion

Post by mdvaden » Wed Dec 12, 2018 2:15 am

Brett Mifsud wrote:Greeting all
With regards to this latest claim for the height of Centurion, I’d love to say it is over 100m, even the 100.5m Yoav claims it is. However, I believe he’s got it wrong.
Brett,

I'm glad you chimed in. I was chatting about this with a man Aaron Poole on Facebook, and posted back and forth with Steve Pierce who thought I was doubting them. It wasn't really doubt on part, as much as what I was in their report just wasn't enough to tell me in uncertain terms Centurion was as tall as they claimed.

Also, Aaron shared with me some of the growth rate from the past that you mentioned. And I thought the measure from 2017 to this 2018 measure was almost an explosive increase compared to previous years combined.

In a nutshell, it's not that I don't think it could reach 100 meters. It's just that I have no clue what it's real height is. And that's what I think would be most beneficial for both present and future is to document the height as exact as possible, to keep accurate track of the growth rate. It would be more useful that way.

By the way, thanks for visiting .. greetings from Oregon !!
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Re: Accuracy of Trupulse 360 & Centurion

Post by Brett Mifsud » Wed Dec 12, 2018 3:39 am

Hi Mario
Yes, we really have no idea of its exact height. By the way, Steve Pierce and Yoav already knew about the 2008 and 2014 tape drop measurements and I alerted them to the 2016 tape drop. In spite of this knowledge they've gone ahead with publicising their measurement.

What I can tell you is this: When Tom climbed it in 2008 he got within 1.88m of the top before dropping the tape - and he's very keen to climb it again after all the current fuss! What we don't know is if the same publicity will be generated if the tree turns out to be closer to 99.6 than 100m.

It has even made news with our national broadcaster:
https://www.abc.net.au/news/2018-12-12/ ... n/10604588

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