Several posts in the last few weeks have mentioned the use of a
reticle for determining remote widths, as in tree trunks. Jess
the device in his recent report on the giant tuliptree in Cosby,
wanted to take some time to fully discuss this instrument and
implications for its use.
Jess using Reticle
Jess's father, long-time ENTS member Doug Riddle, is an
(who is particularly fond of gadgets) and has used his monocular
macroscope (hereafter reticle) to check specifications of
components that could not be reached. His is a model made by
PENTAX that is
an 8X30 monocular with a field of view of 6.2 degrees. It has an
scale (reticle) that can be optically transposed across an
object. The scale
runs from 0-4 (mm) with ten graduations between each number.
This gives an
effective resolution of 40 increments. The "zero"
(left hand of scale) is
demarcated by a long vertical line that is useful for
"averaging" the bark
or trunk profile. We found that the extreme sharpness and
clarity of the
scale easily allows optical divisions of each gradation into
10ths (as we do
with clinometers). In our tests Jess and I often estimated to
1/10th gradation. On sharply defined objects 1/100th estimations
entirely possible making the scale extremely accurate. The
then multiplied by the distance and a factor to get the actual
width of the
Our intended use for the instrument was to see if it could be
determining diameter of tree trunks aloft to help measure
volume. Bob Leverett has been extensively testing the RD1000 for
applications and has found a myriad of inherent limitations. The
extremely simple and fits right in with our existing instruments
clinometer) for a low-budget three dimensional measuring outfit.
is- is it accurate enough?
To assess its applications into tree volume modeling Jess and I
series of tests to ascertain the range of use and accuracy. We
duplicates (Jess and I independently) of the following tests:
Width of trees and flat objects
Same tree trunk at various distances,
Window sill at various distances,
Tree trunk; four locations up trunk, each at the four cardinal
Fixed round objects
Steel billboard post; diameter at various distances,
Steel billboard post; volume,
Steel billboard post; volume- laser versus taped baseline.
And finally, the ultimate test;
Tree climb; diameters and volume versus climb data.
Rather than go into detail of each test and lose everyone on the
list I will
summarize the findings of each test. But I'll tell you know we
upon a revolution in volume modeling. The device tested well
expectations. Accuracy does not diminish with distance and is
to distance or scale size like the RD1000 (it also costs much
less). It does
not use batteries and is very easy to carry.
Here are the results of the above tests.
Width of trees and flat objects
Same tree trunk at various distances
Target: white oak measured diameter (w/ tape) at 1.007 feet.
error was 5.8 % while working at 30 feet. After getting into the
range of the device (45'+) error dropped to less than 2.5% (.3
Average diameter over a range of 30 feet to 165' was 1.007 for
Will and .999
feet for Jess. Widths were slightly overstated at long distances
slightly under at close distances. Jess and I differed by
slightly over 1%
in our reticle readings. This was the first time either of us
had used it.
But, trees are not round and thus the diameter of 1.007' was a
not an actual width. So the next test was of a flat object with
Window sill at various distances
Target: a white window sill taped at 73.5 inches wide. We
measured it from
125-200 feet away at 15 foot intervals. Will averaged 73.49
inches and Jess
73.52 inches. Maximum error was .15 inches over for Will and
under for Jess.
Jess and flagged trunk
Tree trunk; four locations up trunk, each at four cardinal
Target: a relatively straight tuliptree measured from four
locations, 90 degrees different from each other. Four locations
base to over 20'were marked with yellow flagging tape
perpendicular to the
trunk. The girth of each point was measured with a tape. Each
was then measured with the reticle from four directions paired
sides (same baseline distance). Jess and I independently
point. The maximum difference in reticle scale reading between
measurements was a miniscule 0.015 of a gradation so I will
results. Since volume determination is based on girths (obtained
to diameter) I will summarize the results in girth. I will point
parts of the trunk were elliptical with a maximum linear
between 90 degree measurements being over 5.6 inches (23.34
inches one way
and 17.4 in the other). The measurements obtained at opposing
nearly identical with a maximum difference of just 0.049 feet
which was incidentally obtained on a "shot" through
brush. Here are the
Trunk point Reticle girth Taped girth Elliptical offset
20.08' 58.81" 61" 3.2"
14.58' 63.16" 64.625" 5.6"
6.58' 66.21" 66.375" 1.92"
Base 77.04" 77.5" 1.8"
I suspect the volume calculated from the two opposing reticle
ellipse) would more accurately represent the actual volume since
the tree is
not round. Taped girths would tend to overestimate the volume.
later field tests may show otherwise (see below).
Fixed round objects
Target: steel billboard post; diameter at various distances
The post was taped to 3.01 feet in diameter and assumed to be
Reticle indicated a diameter of 3.02 feet with a maximum error
of 3.06 feet
(+1.3%). We measured at distances of over 280 feet.
Steel billboard post; volume
Using the rangefinder and clinometer we measured the height of
post and various points along the length with the reticle to
volume. Girths used in the calculations were on the average .05
feet off (.6
inches circumference) which yielded a volume of 456.65 ft3 over
a length of
63.2 feet. Actual volume based on the taped girth and baseline
ft3, indicating an understatement of .7% or 3.23 ft3.
Steel billboard post; volume-laser versus taped baseline
Interestingly, the taped baseline with reticle girths overstated
volume by 4.1%. We are baffled by this and suspect human error.
And finally, the ultimate test.
Tree climb; diameters and volume versus climb data.
Will setting the flagging
Jess and I selected a huge hemlock tree with easy access and
test the reticle against a tree climb. I climbed the tree and
set up five
marked intervals like in the tuliptree above. I wrapped yellow
around the trunk and measured the girths at that point. We then
set up the
reticle in two locations roughly 90 degrees from each other so
we could get
the widths at each point and determine the elliptical numbers.
calculated the volume of the marked section using the climb data
reticle data. We were impressed!
Trunk fro first Position
Trunk with flagging
I'll cut to the chase. For the 47.5 foot long modeled section
the climb data
indicated a displacement volume of 535.74 ft3. The reticle data
Will indicated a volume of 529.7 ft3 and for Jess, 526.32 ft3.
difference was 9.42 ft3 at the most, an impressive difference of
These numbers were from a taped baseline to the middle of the
trunk with no
lean taken into account (very minor). The laser distances were
longer indicating a long reading that must be calibrated. As
such, the laser
(uncorrected) estimated the volume as 562.99 ft3 for Will and
559.34 ft3 for
Jess. Still, the results were within 5.1% of the climb data. One
numbers for the lasered hypotenuse distance was erratic and
added nearly 1.8
feet to the length of a large section which added about 22 ft3.
this section alone would reduce the "error" to a 4.3
ft3 overestimate or
less than 1% off.
Obviously, the more we use it and refine our techniques and
nuances of the equipment we should be able to obtain remote
estimations within 95-99% of a climb. Jess and I were hoping for
accuracy and with a bit more practice should be able to obtain
I am not sure that further testing of the reticle is needed but
a visit to
trees that have already been climbed and measured could prove
Comparing a random series of shots at various locations to
and compare it to the climbed results could give insight into
how many shots
are needed and where. The problem is we never really know the
volume. To us, the reticle seems to be the best option other
Jess and I have already begun to model hemlocks and Jess has
big tuliptrees for main trunk volume. We intend to use the
extensively in Congaree next month; loblolly pine and cherrybark
oak are on
Where can you get one?
Jess and I searched with no luck for the Pentax model. It is no
manufactured. We did find some through a company named Cole-Parmer
Instruments in Illinois and I ordered one. I also ordered one
Meadows Company (1-800-241-6401) which has miraculously just
their new 2006 catalog. The biggest issue with all the models is
focus, as the reticle scale will go out of focus at close
units, when used as telescopes, have the reticle in focus when
infinity. The unit from Cole-Parmer (made by Specwell) has its
focus set at
over 300 feet- not useful for ENTS. Although a camera repair
the focus can be reset I returned the Specwell units in favor of
Meadows model which arrived this week. The Ben Meadows model
6JB-221152, page 573) has the advantage of a wider field of view
Pentax (hence more gradations; 0-50) and a scale that starts at
0 on the
left (the Specwell model had "0" in the center- very
awkward). It is also
$70 cheaper! The focus is good as set so it can be used
instantly. I did
retain the tripod adapter (a fancy clamp) from Cole-Parmer to
securely to the tripod (Item # WD-03099-62 on website). However,
attachments can be made with wood and straps.
To check its accuracy Jess and I have put the "new"
model through some
tests. The first test (diameter of a steel light pole) sucked.
We made a
mistake of not visiting the pole first- it was not round! We
that the factor supplied with the instrument was significantly
may have been a relic manual from previous model that was not
this model. In any case, Jess' math prowess solved the problem
and the new
factor revealed excellent results in the next test of a 5' wide
Widths were no more than .26 inch off over distances from
100-200 feet away.
The average error was .0765 inch. Looks like it will work just
Field observations and techniques
The narrow field of view in Doug's PENTAX model (6.2 degrees)
being rather far back from large trees. So in our search for a
model for our regular use we looked for one with a wider field
of view. The
first model we ordered (Specwell) had a field of view of 8.2
more useful for large trees at close distances. The scale could
span a six
foot wide object at 95'. However, as mentioned above, we soon
unit's focus with regard to the reticle set way to far away.
sense for its use as a telescope but the reticle scale was sharp
over 300 feet away. Focusing in on closer objects would
eliminate the scale
from view. Not good. The Ben Meadows model has a wider field of
Doug's but not as wide as the Specwell model. I am not sure of
specifications but it is substantially wider. Being able to work
reasonable range is helpful since the farther you have to move
back the more
obstacles position themselves between you and the tree.
Another crucial component of the ultimate accuracy of this
getting an accurate distance to the tree. We have come to
estimating to 1/10th yards is entirely reasonable by finding
checking against the eyepiece of the reticle, which is
means that a properly calibrated laser will be highly accurate
even at +/- 1 yard resolution. When modeling, we measure to the
the trunk. All points are referenced to a common base target
usually a tape or flagging wrapped around the tree. All
any location can then be easily referenced against each other.
the aerial targets are measured by placing the clinometer on or
next to the
reticle and using the distance to the nearest 1/10th yard. We
the taped reference point to compare the actual girth to the
estimation. We have found that they are often just an inch or
Some limitations which we find to be rather minor are that you
MUST use a
tripod (and not in the wind!). The reticle is so precise that a
will throw off the measurements. Even standing on the adjacent
can shift the tripod! We are using a tripod made by Samsonite
Circuit City) that has a functional height of 66"- good for
the neck! You
also need a vantage point with a view of as much of the tree as
This can take some time to find, but once the reticle is set up
measurements can be made from one side. These points can then be
another set-up and if a common reference be found, elliptical
be used for volume calculations.
Jess and I have successfully used the reticle in hemlock forests
light conditions, but the reticle can be hard to see if it is
dark in the
background. Also, laser distances can be hard to obtain through
branches. As such you are limited to portions of the trunk that
can both be
seen with the reticle and hit by the laser. We have not found
this to be a
huge issue, mainly because there is not much volume in the upper
portion (of conifers) and more measurements will not gain but a
increase in accuracy.
So, there it is formally introduced. Nowadays the device is not
left at home
when we go into the woods. It has become a standard part of our
arsenal. More significantly though is how it has changed the way
we look at
trees. With more and more experience in modeling we can now
relationships of tree growth (volume) within and between
species. We intend
to begin determining annual volume accrual by accurately
displacement volume and coring the tree for age. Questions start
themselves; at what age and on what sites do tuliptrees grow the
How much wood can they grow in a year? Where do they put down
the most wood?
Do they slow down or increase wood production over time? If so,
by how much?
Could they grow faster when they are big? What about white pine?
.Oh no, Bob
Leverett will have an aneurysm.
Now it appears that we have the tools to answer these questions.
Will Blozan and Jess Riddle