A big oops   Robert Leverett
  Sep 02, 2005 08:26 PDT 

ENTS:

      On Wednesday and Thursday Monica Jakuc were in the Adirondacks. We
camped at Moss Lake on Wednesday evening as the remnant of Katrina
passed through. On Thursday, we visited the Cathedral Pines between 7th
and 8th Lakes on the way back. I re-measured the tall pine there. It is
150.8 feet, down from over 152. It is holding its own.

      Both going and coming from the Daks, we stopped at Pack Forest
near Warrensburg and walked the nature trail. On the return leg of our
trip, we had plenty of time, so I set out to model the huge Grandmother
Tree in Pack Forest with my trusty RD 1000. The Grandmother Tree is very
large. It measures 17 feet around at 2 feet above its base and is now
13.8 feet around at 4.5 feet above its base. At 6 feet above its base,
it is 13 feet around. Above 6 feet I used my RD 1000, but soon noticed
that I was getting diameters that were simply too high for the heights
above base. I felt an uneasiness in the pit of my stomach, suspecting
that I was doing something wrong by treating potentially any spot along
the trunk as a baseline. The instructions that come with the instrumet
are explicit enough. They call for first entering the horizontal
distance to the trunk. That distance is locked in. Then the instrument
is pointed to the base ofg the tree and the angle locked in. All the
measurements proceed from that point. Subsequent scans, up or down, give
height above or below the horizontal and the corresponding diameter.
Stopping and locking at a point along the trunk allows the user to
expand or contract the diameter scale to fit the trunk. The diameter
shows in inches or centimeters. I began using the instrument this way,
but then began going directly to a point up the trunk and using it as
the starting point. I began to get some fat diameters. I began
switching modes from the former method to the latter when I discovered
that the RD 1000's tilt sensor wasn't all that accurate. Big mistake!

      I must now go back and re-model all but the Jake Swamp tree. Oh
Boy! I doubt the volume I computed for the Ice Glen pine since I'm
relatively sure that I mixed the two methods of setting the baseline.
Anyway, when I confirmed my mistake on Sunday, I took diameter
measurements after first zeroing and at the horizontal. The big
Grandmother tree computes to 920 cubic feet in trunk and limb volume,
falling short of 1000 cubes. However, I found a vantage point at a
higher elevation that any previous measurement and confirmed the huge
tree at 151.2 feet. The last time I measured it was 5 growing seasons
ago. I had it at 147.2 feet and 13.6 feet in circumference. I doubt that
I hit the absolute top. It probably was about 148.5 then. Anyway, it now
joins the 150 Club and the 12 by 150 club. It also joins the Tamworth
Pine in NH and the Cornplanter pine in PA as the largest single-stemmed
pines that we've measured in the Northeast.   

      The height of the Grandmother tree was mis-measured by the
forestry staff of SUNY and then the erroneous measurement was
subsequently over-promoted in their literature. SUNY had the tree listed
as 175 feet tall at a time when it was, in fact, about 146. Jack Sobon
picked up their error when he measured the tree with his transit. The
way the tree was saved is a story in an of itself, which I'll relate in
a future e-mail.

      However, in terms of giving it attention, we shouldn't penalize
the huge Grandmother tree because of past measuring mistkakes -
regardless of who made them or how they were made. The Grandmother tree
stands as one of the great white pines in the East.

      One thing that puzzles me about the RD 1000 is how the mathematics
is done internally. Suppose all diameter calculations stem from the
following process. First the horizontal (level) distance to the tree is
set as a number in feet or meteres into the RD 1000 and then the device
is tilted to the base and that value locked in. The result would be the
establishment of a right triangle from the eye to the trunk of the tree,
down to the base and back to the eye. Scanning up the trunk would use
the tilt sensor to determine the angle of inclination. The distance to
the tree at eye level would be the constant base. Reaching a point up
the trunk would utilize the base and the angle as determined by the tilt
sensor. The scale would be calibrated to the distance and the angle. If
the angle is off, then the computed height would be off and the
subsequent diameter as read from the scale would be off. That's scary.
The accuracy of the diameter reading would be directly tied to the
accuracy of the tilt sensor.

      So far my satisfaction with the instrument has been the diameters
it has yielded of objects close to eye level. I obviously have lots of
testing left to do. Anyway, the Grandmother tree is a great tree.

Bob


Robert T. Leverett
Cofounder, Eastern Native Tree Society
Re: RD 1000 musings    jarred trout
   Sep 08, 2005 06:13 PDT 

look up in the sky and what do you see?

big ol pine crown left of the shag hickory

who is that man with his head stretched up long

what kinda music is that gorilla song

how many years has he been doing this gig

answer is simple

since ‘jake swamp” was a twig

started out slow and now like a train

in the cold winter snow

and in the sweet summer rain

got him some toys

and we know its true

more numbers and data

and diameters too

what is the newest one on the block

heavy and “silviculture sexy” perched on that rock

it’s the RD 1000 with all its fan fare

not for the novice

only tree angels will dare

use it to know and to keep on track

warranty is up

he won’t send it back

got it from his girly friend

and aint that so sweet

can you hear them in the green together

just shuffling tree feet





done with my musing

and back to work

dreaming of Mohawk

where all spirits lurk

maybe I’ll make on some sunny day

and see him and his lady

taking inventory

the RD 1000 way



‘y’all ding dang ol Ents people is okay

thanks again for stayin in the forest

and not being on the water

spookin’ the fish



love,

jarred trout
Testing the RD 1000    Robert Leverett
   Sep 08, 2005 06:36 PDT 

Ed, Will, Jess, Lee, et al:

The table below illustrates the challenge we face to getting accurate
diameter measurements with the RD 1000. I need to set up more tests to
investigate the degree of the challenge. So stay tuned. Lots more
coming. But now to yesterday evening’s experiment.

The diameter of a silver maple in my yard, as measured with a D-tape at
4.5 feet, is 32.8 inches. Before taking that measurement, I went to a
spot 66 feet from my tree and set 66 feet into the Rd 1000. Then I
invoked the routine to measure diameter. One expands or contracts a red
diameter scale superimposed on the trunk of the target tree by clicking
a right or left button. When the scale just covers the trunk at the
point, the diameter can be recorded. At 66 feet my aging eyes saw the
scale just covering the trunk at a scale reading of 32.7 inches. Please
remember that I got this reading with the RD 1000 before I actually
measured the tree. I didn't want prior knowledge of the diameter to
influence me in settling on the scale width that just masked the trunk
at the 66-foot distance. Taken just by itself, the 0.1-inch difference
between the scale reading and the D-tape measurement is a good
confidence builder. However, suppose I was one click off from the
reading at 32.7 inches. What would I have read the diameter as? Well, I
did the clicks. The lower one gave a diameter of 32 inches and the upper
one gave 33.5. In other words being one click off would have produced a
difference of 0.7 inches on the low side and 0.8 on the upper side. From
the 32.7-inch point, I shrunk the image by two clicks, recorded the
result and then went back to the 32.7 and increased by two clicks and
recorded the result. The range of diameters I got was 31.2 inches to
34.3.

I then moved back to 81 feet and repeated the experiment and moved back
to 100 feet and repeated again. The table below summarizes the results.
I hope the table won’t be garbled when it goes into the e-mail. If so,
I’ll present the results in a different format.
Distance
(ft)		 <----------- Clicks ----------->
-2 -1 0 1 2 Difference
between adjacent values
66 31.2 32 32.7 33.5 34.3 0.8
81 30.8 31.7 32.6 33.6 34.5 0.9
100 29.9 31.1 32.2 33.4 34.5 1.1
Measured diameter = 32.8 inches

         So, let’s see. What conclusions can be drawn? If I had started
measuring from 100 feet away from the trunk, my choices for diameter
measures at the chosen spot on my tree would have been: 29.9, 31.1,
32.2, 33.4, and 34.5. No amount of expanding or contracting the scale
would put me closer to the 32.8 inches actual diameter. At a distance of
100 feet, seeing the edges of the tree become difficult, so it is not
guaranteed that the reading would have been 32.2 or 33.4. However, it is
likely that I would have settled on one of those two measurements and
would have been off by 0.6 inches. Looking 100 feet up a trunk in dim
lighting with clutter in the way, which is the set of conditions I
experienced for some of the pines I recently measured, could easily
cause me to be off by a couple of clicks.

        It is becoming increasingly apparent that multiple readings will
need to be taken and from the closest possible distances consistent with
seeing the edges of the trunk and subject to the terrain that may not
allow a closer approach. For the tall pines that I’m modeling, I seldom
will get a reading higher on the trunk than 120 feet. So my next
experiment will be a more rigorous investigation of the pattern of scale
readings at distances of 30, 60, 90, and 120 feet.

   The solution to getting fairly accurate diameter readings on trunks
that are over 80 or 90 feet away is going to occupy a lot of my time in
the coming weeks. In the interim, you should treat any volume
measurements I post for the big pines with a healthy amount of
skepticism.

Bob


Robert T. Leverett
Cofounder, Eastern Native Tree Society