between tangent and sine-based calculations Error Spreadsheet
26, 2004 10:27 PST
Our discussions on the
difference between sin and tangent-based
calculations and Will Blozan's recent suggestion to compare what
tangent-based height calculation would have been in our
treating the point shot with the laser to have been vertically
base led me to run comparative calculations on a sample of 1,330
measured with laser and clinometer. From an original larger
eliminated those measurements in which the measurer would have
closer to the trunk than a chain's distance (66 ft) or at an
angle of to
the crown of 65 degrees or more. I considered these two
situations to be
improbable measurements from the standpoint of an experienced
the tangent (% slope) method.
The results are as follows:
Differences between sin-based and tangent-based calculations for
height. Covers above eye calculations. Differences are in feet.
1-1.99 2-4.99 5-9.99 10-14.99
15-24.99 25-65.99 TOT
Pct Tot 9.2% 9.8%
25.0% 27.7% 12.6%
Cum Pct 9.2% 19.1% 44.1%
Max diff: 65.32
Ave diff: 8.30
The average of the absolute value
of the differences is 8.3 feet.
The max difference is a whopping 65.3 feet. These statistics
ABOVE table of percentages tell most of the story. It is
possible to reduce the error of the tangent-based calculations
cross-triangulating the crown, but even that method has its
visibility of the same crown point from sufficiently separated
being the primary. Will Blozan and I did the crown
for several years and described the method fully in:
Forest Monarchs - A Guide to Measuring Champion Trees".
The next series of charts
will look more closely at subsets of
these measurements. Please stay tuned. The above is enough for
I'll send the Excel
spreadsheet holding the 1330 measurements to
Ed in a couple of days.
Difference between... MY REPLY
27, 2004 14:52 PST
The numbers came out kind of distorted in my email. However, the
very significant, especially given that in our ENTS measurements
top has already been identified- a task that can take hours with
cross-triangulation. Impressive and compelling!
I think we should present a synopsis of our findings to the
deliver it to certain parties for their "review". We
have a strong case, one
that should be spread to the public. I am ready for ENTS to make
more of an
impact in the tree related "playing fields". I also
think a scientific push
can be made as well as in ecological mensuration (nest heights,
layers, etc.) and in more utilitarian fields such as forestry.
Also, how accurate are waterfall heights in the East? I have
seemingly outrageous heights claimed for waterfalls, and have
about the accuracy. I suspect I do not want to know...
Difference between tangent and sine-based WILL IS ALMOST READY!
27, 2004 19:36 PST
Bob, John, ENTS,
I have 10 trees of 10 species set up in EXCEL for calculations.
chosen 5 gymnosperms (e. hemlock, C. hemlock, red spruce,
loblolly pine, and
white pine) and 5 angiosperms (tuliptree, white ash, red oak,
To make my comparisons similar or identical to yours I need to
know if you
have corrected for slope in the conventional height
calculations. I have set
it up both ways, slope corrected and not, but I have some pretty
angles on some of the trees. I could select less steep angles,
but the steep
tree measures are good to know as well, and are not undoable
What would be good to know also is to
"cross-triangulate" with the laser
from two 90 degree opposing angles (same top) to map the top
relative to the
base, and then calculate the range of error over 360 degrees
tree. We would need to pick a "pointy topped" tree for
this with a prominent
I have also looked at the average lean, both + and - from the
even with 10 samples the average is usually less than 2 feet. I
very interesting, and the greatest lean is actually in the e.
feet). Some of my red oaks have a 30' "lean"!
Also, I tend to shoot the base at the midslope on the side of
the tree, not
the closest portion. This way, in my calculations, I do not need
for the radius of the trunk.
More to come!