Macroscope 25 vs RD 1000   Robert Leverett
  Feb 10, 2006 06:31 PST 

Will and Jess,

   I ran some more tests on the Macroscope 25 vs the RD 1000 at long
distances and less than ideal visibility - a kind of worst case scenario
for the instruments. The results are summarized below.


Dist Diam Error Instrument
Rng-ft   Rng-in   Rng-in

226-312 14-44.7 0.170 Macroscope
226-312 14-44.7 1.220 RD 1000

   At 0.17 inches, the average error for the macroscope reflects the bad
visibility rather than the instrument. I was fairly pleased with the RD
1000's performance. I feared that the average error might be even more
at great distance.

   For the range of work we do, for the Macroscope 25, it boils down to
visibility. If we can see it, we can accurately measure it. With luck,
this Sunday, I hope to measure this past season's growth of the Jake
Swamp tree. Should be able to do it to the nearest half inch.

Bob

       


Robert T. Leverett
Cofounder, Eastern Native Tree Society
RE: Macroscope 25 vs RD 1000   Will Blozan
  Feb 10, 2006 22:57 PST 

Bob,

Are those numbers and error ranges for width or diameter? If diameter, they
are not all that meaningful for absolute error.

Will
Back to Will with buried question for Pamela   Robert Leverett
  Feb 13, 2006 06:12 PST 

Will,

ANSWER TO WILL'S QUESTION:

They were diameters, and as a consequence, I completely agree with you
that they aren't very meaningful. I did more tests over the weekend. The
results follow.

NEW MACROSCOPE VS DENDROMETER TESTS:

   Object:               Birch tree (diameter)
   Distance:                  58.7'
   Actual diameter:           13.8"
   RD 1000                    12.8"
   Difference                  1.0"
   % error of act              7.3%
   Macroscope 25              13.1'
   Difference                  0.7"
   % error of act             5.1%

   Object:               Paper on same birch tree (flat target)
   Distance:                 58.7'
   Actual diameter:          11.0"
   RD 1000                   10.8"
   Difference                 0.2"
   % error of act            1.9%
   Macroscope 25             11.1
   Difference                 0.7"
   % error of act            0.9%

   Object:               Stick on cottonwood (flat target)
   Distance:                 77.2'
   Actual diameter:          18.0"
   RD 1000                   19.7"
   Difference                 1.7"
   % error of act            1.9%
   Macroscope 25             18.1'
   Difference                 0.1"
   % error of act            0.9%

      When the target is well defined, I'm consistently getting errors
of under 1% for the Macroscope 25. Based on your and Jess's tests, I
expected that. I probably won't get quite the results that you two get
until I get new glasses. However, bad vision and all, the error has been
as low as 0.3% for significant distances. The Dendrometer's error is
usually around 2%, sometimes a little less. With a better tripod, I
might slightly reduce the error for both instruments.

     One lesson that comes through over and over (not that we didn't
already know it) is that trees are NOT circular in cross section and
that any serious attempt to model the volume of a trunk or a limb must
take lack of circularity into account. The wide variation that I get
from taped circumferences converted to diameters as compared to the
measurements of diameter that I'm getting with the Macroscope 25 versus
the very narrow variation in actuals versus measured for flat targets
serves to further illustrate how often trees are out of round.
Instruments that are designed around assumptions of a circular cross
section are going to lead to measurement errors. I suppose that they
rely on a lot of averaging out over large numbers, so that over many
trees maybe the volume errors are negligible, but not as applied to
individual trees, so that volume tables that assume circularity and a
standard rate of taper are of no value to ENTS. I discovered that for
myself about 9 years ago, but wasn’t so confident then in proclaiming
the inapplicability of table data to single tree measuring. But maybe I
was missing something. However, time and testing by the three of us
(you, Jess, and me) has amply shown that we weren’t missing anything. We
are sentenced to ahve to go it alone.
Tree Trunk Assymetery   Edward Frank
  Feb 15, 2006 14:46 PST 

Bob,

You have made a couple of recent posts concerning the asymmetry of tree
trunks. What kinds of things could be looked at in this context/? How
asymmetrical are individual trees? Do some species tend to have more
asymmetrical trunks than others? Does the degree of asymmetry vary with
age/ What about other factors like stand density? Height to diameter ratio?
Is the asymmetry oriented in a preferred direction - north/south or
upslope/downslope? Tree canopies are often asymmetrical. Does the
asymmetry of the trunk relate to the asymmetry of the crown? Are the trees
equally asymmetrical along their entire height? How does asymmetry vary
through time (you could measure cookies to determine this one) There are
lots of potential things to measure...

Ed
Re: Lowes & Cannon Creeks, GSMNP, TN   foresto-@npgcable.com
  Feb 15, 2006 22:23 PST 

Ed-
One way to look at this issue is to assume that in the East, barring
broadscale windevents and other climatological extremes, a forest grows one
tree at a time...as one senesces (from whatever cause/disturbance), another
one has an opportunity to fill the void, fresh exposed rich soil, new dose of
sunlight, to the victor seed goes the spoils (space).
Where that seed that grows most successfully falls, determines its 'space' and
its space determines how the tree fills it. Seed fall may approximate random
chance, but seed germination/growth success, probably doesn't. Topography,
aspect affect solar incidence angle (warmth, energy) and tipover mound
microtopography probably has significant impact on success.
Once the tree roars up into its space, its neighbors constantly remind it of
its space constraints, as they 'wear' at each other.
Assymmetry should be expected, and the lack of it cause surprise...
-Don
Tree trunk asymmetery, Macroscope 25, more tree conversations   Robert Leverett
  Feb 16, 2006 06:14 PST 

Ed,

Whew! You've given us a decade's worth of measuring possibilities in
your enumeration of asymmetrical possibilities. As it is, I'm lagging
behind the plan I had for myself to begin simple measurements of trunk
asymmetry. Haven't forgotten it though. Will and Jess, HELP!

Will and Jess,

On another measuring theme, yesterday ENTS reached another milestone.
After missing a Forest Reserves meeting, I consoled myself and went to
MTSF to measure the prior year's growth of the Jake Swamp tree using the
Macroscope 25. The weather was perfect. 

The instrument worked marvelously well. I measured 8
growth candles atop Jake's crown. The distance to the targets varied
from 66.5 to 69 meters and the reticle values varied from 0.3 to 0.5
millimeters (I use the metric scale with the Macroscope 25). Converting
to English units, the two highest candles had surprisingly differing
lengths: 10.6" and 17.7". The full list of candle measurements follows:


    10.6", 17.7", 11.2", 16.9", 17.6", 10.4", 15.5", 10.9".

   The average of the above is 13.8 inches. There is little doubt that
Jake will reach 168 feet this year. With luck, it will make 170 by the
end of 2008, 2009 at the latest.

    After measuring Jake, I measured 3 candles on the Massasoit tree:
13.8, 11.5, and 9.2 inches. A white pine in front of the Nature Center
yielded 14.8 and 14.9 inches for its two very conspicuous tops.

   The reticle is ideally suited to measure candle growth. More on
geometry considerations using the reticle for vertical measurements at
an angle as opposed to horizontal ones in the next e-mail.

   With the confirmation of the Macroscope as reliable for new candle
growth measurement atop our tallest trees, I can finally make good on my
promises to DCR. Lots of new possibilities. When will it ever end?

Bob
Rd 1000 vs Macroscope 25   Robert Leverett
  Mar 07, 2006 04:46 PST 

Will, Jess, Ed, et al:

   I've added a few more tests of the RD 1000 versus the Macroscope 25.
Through 30 tests, the average of the absolute values of the differences
between the two instruments is 1.07 inches. That average covers targets
that are from 8 to 34 inches in diameter and shot from distances of 54
to 312 feet. The difference between what the two instruments return is
most pronounced for large diameter objects. For example, the average
difference for targets 24 inches or more in diameter is 1.99 inches.
That is almost double the overall average. This makes me extremely weary
of my volume modeling of the big pines and hemlocks that I've done so
far in MTSF, MSF, Ice Glen, Bullardwoods, etc. Yet, it is a cut and
dried issue. I got almost exactly what BVP modeled for the Thoreau pine.
In fact, my number was slightly lower than his. So, since the pattern is
not uniform, I cannot say for sure that all my big tree models are off
by a certain percent.

   The RD 1000 is a fun instrument to use and definitely has a role in
what I'm doing, but some kind of compensation factor must be developed
to correct for large objects and long distances. The difference between
the two instruments illustrates the problems we encounter with reliance
on sophisticated, versatile instruments. Internal algorithms and design
tradeoffs can compromise accuracy without trusting users being aware.
One needs to be aware of how much accuracy they are willing to surrender
in order to enjoy a plethora of "Gee Whizz, it makes coffee too"
features.

   Having said this, use of the RD 1000 at distance of 65 to 85 feet on
targets of 6 to 20 inches does yield good results.

Bob
The daily stats   Robert Leverett
  Mar 08, 2006 05:33 PST 

Will, Jess, Don, Lee, et al:

   More comparison tests of the RD 1000 vs the Macroscope 25 were
conducted last evening. The edition of 4 tests puts the average
difference between the two instruments at 1.1 inches and that difference
represents 4.86% of the Macroscope average diameter.

   If more larger objects are shot at a distance, the average difference
between the Macroscoope 25 and RD 1000 will grow. But if the size
classes stay well mixed, the average difference (actually the average of
the absolute values of the differences) will likley stay around 1 inch.
At present, that's the number I'm keeping in my noodle.

   How does the accuracy of each instrument compare with the direct
measurement of the target objects? Well, a tree trunk measured yesterday
evening with a D-tape was 32.52 inches. The Macroscope 25 reading was
32.72 and the Rd 1000 was 33.3. The 0.2 inch difference for the
Macroscope represents 0.6% of the taped diameter. The 0.78 inch
difference for the Rd 1000 represents 2.3% of the taped value.

   Since the tree trunk isn't absolutely circular, the D-tape
measurement yields only an approximate value so that comparisons of the
0.2 versus the 0.78 inch differences is a little misleading.

   Measuring control objects that are either circular or flat is showing
that the maximum absolute error from the Macroscope does not exceed 0.5
inch and that the average error is less than half that - sometimes less
than a 1/10th of an inch. The Macroscope is consistent. Large errors
tend to be problems with seeing the target. However, the maximum
absolute error of the Rd 1000 can reach 3 inches, although that is truly
extreme and is for large targets seen at distances of over 100 feet. The
average error is around 1 inch.

   The bad news from all this is that the volumes of the larger trees
that have been modeled with the Rd 1000 are highly likely to have been
overstated. So it's hi-ho back into the forest I go to figure out a new
set of volumes for an old set of trees.

Bob
RE: Rd 1000 vs Macroscope 25   Robert Leverett
  Mar 08, 2006 10:25 PST 

Don,

   With one exception, the 35 measurements are comparable only among one
another. I was not clear on that point in my communication.

   I've now tested the Macroscope 25 many times against directly
measured objects and am very confident that its error range is within
+/- 0.5 inches for distances approaching 300 feet. Errors in the 0.35 to
0.5 range are due to human error as opposed to instrument limitations.
Target visibility is the biggest source of error. However, most
Macroscope 25 measurements are accurate to +/- 0.2 inches on objects
between 100 and 250 feet. Objects that are too close are not clear in
the monocular, so one does have to maintain one's distance.

   Once I start re-measuring the pines, I'll consider the Macroscope 25
as providing the equivalent of a direct measurement, but I'll also
re-shoot with the RD 1000 so I'll have a side by side comparison for
each tree to report.

   Despite its limits, I really like the RD 1000 and see its utility for
jobs that fit into distance and diameter windows, with distance being 60
to 100 feet and a diameter being 6 inches to 30 inches. The 6 inches can
be dropped to 4 and the 30 can be increased to 36 if one is willing to
accept a larger error.

   I'm anxious to re-measure the Grandfather pine in MSF. I have a
feeling that the volume is going to go down by 75 to 100 cubic feet.
That would drop it below 1000 cubes. Rats!! If the weather forcast holds
out, it may be off to MSF old Bob goes this Sunday.

Bob
    


Don Bertolette wrote:
 
Bob-
Stupid question time...are these measurements comparative between themselves only, or are you comparing these two measures against actual diameter/circumference measures?
-DonB