ENTS,
The TruPulse 360 combines a
laser rangefinder, inclinometer, and compass to provide a host of
useful measurements for two points relative to one another in
3-dimensional space. Returns for the two points include:

1.
Their vertical, horizontal, and slope distances apart,

2. The
angle of inclination of the second point relative to the first,

3. The
azimuth of the second point relative to the first.

Of course, the 360 can also
separately return the individual statistics for each point
relative to the measurer's location, i.e. the vertical,
horizontal, and slope distances, the angle of inclination, and the
azimuth of each point relative to the measurer. These are the
measurements returned by the TruPulse 200. However, the extensive
of measurements for the two points in 3-dimensional space is
impressive. If the advertised accuracy of the instrument holds up,
then the price tag of $1,500 for the 360 is worth it, at least for
a very serious tree measurer who wants to model the forms of tree
and make computations on limb length.

The rangefinder of the 360 is
rated as accurate to within +/- 1 ft – same as the TruPulse 200.
But in practice, for the 200, the accuracy is usually less than
half a foot. I would say +/- 0.3 feet. I presume the same will
hold true for the TruPulse 360 and is for the one that I tested.
Inclinometer accuracy for both the 200 and 360 models is rated as
+/- 0.25 degrees. I am unsure of this claim. Getting pinpoint
angle measurements is a bit more difficult than for distances, but
I'm confident that the instrument is accurate to +/- 0.5 degrees
and I will eventually confirm the advertising claim.

The TruPulse 360 compass is
rated by LaserTech as accurate to +/- 1.0 degrees. I didn't get a
chance to thoroughly test the compass accuracy, but I will say
that the accuracy sometimes fell within +/- 1 degree and sometimes
outside that range. Magnetic interference can quickly spoil any
compass’s performance and the TruPulse 360 is no exception. So,
precautions must be taken or compass readings will be unreliable.

In addition to the delightful
deluge of measurement returns – something for everyone, the
optics of the 360 is superb, the best of all my lasers. Finally,
data from the 360 measurements an be downloaded via a data link.
So, with the 360, you get a kind of soup to nuts menu of returns.
Is the instrument worth its hefty price tag? Well, if the
3-dimensional returns are sufficiently accurate – absent of
magnetic influences, for me, the answer is yes.

From the limited tests that I
made with the 360 that LaserTech loaned me, I am willing to take
the gamble and purchase one when it is commercially available.
However, I still want to better determine the accuracy range of
each feature. This brings to mind a question about testing. Do we
have good testing procedures worked out for these instruments? We
can always improve on what we have, but I think that the following
test procedures are adequate to allow distance, angle of
inclination, and azimuth to be checked for the 360.

**Distance:
**

In testing distance accuracy, I
recommend shooting to a variety of targets at carefully measured
distances in varying lighting conditions, foreground and
background, and with the target oriented to different angles. Our
tree targets vary greatly in shape and reflectivity and we shoot
them in varying conditions of foreground and background lighting,
orientation, and inclination. One must look for consistent
patterns and adjust returns accordingly. For example, my TruPulse
200 tends to shoot short by about a foot on distance shots of 150
feet or more. But for closer targets, it is amazingly accurate. I
presume that the 360 laser will be no different. But, if in doubt,
test, test, test.

**Angle of inclination:
**

One test of the inclinometer is
to shoot to the top and bottom of a vertical wall of known height
and known distance away. Get both top and bottom distances and
angles and apply the formula shown below.

D_{1 }= distance to top

A_{1} = angle to top

D_{2} = distance to
bottom

A_{2} = angle to bottom

H = height of wall

A = computed angle between top
and bottom of wall from vantage point.

Compare A to A_{1}+A_{2}.
If the inputs to the above formula are accurate to a high degree,
then A will be a good test of the accuracy of the inclinometer in
shooting the top and bottom of a tree. The more accurately you can
read the distances and angles from the instrument, the better the
test will be. Again, this test is appropriate to the sine top -
sine bottom method of measuring tree height.

There is also the good method
for checking to see if a clinometer accurately measures level. Ed
Frank has described the method before in e-mail exchanges and may
wish to present it again. I have it diagrammed out in my
Dendromorphometry presentation, but will not repeat it here.

**Azimuth:
**

TheTruPulse 360's compass can be
quickly checked for the direction of a single point by using a
high quality engineer's compass and simply comparing readings from
the TruPulse and compass. The key here is to measure the direction
of the point with the engineer's compass taken on the level. The
actual point being measured for azimuth with the TruPulse can be
above or below eye level. The 360's compass allows for virtually
any orientation.

**Relative Azimuth:
**

Relative azimuth, the azimuth of
point #2 to taken from point #1's location, is trickier since both
points may be in the crown of a tree so that you may not be able
to get to point #1 to look toward point #2 for a compass reading.
However, there is a way that relative azimuth can be checked. The
following formulas allow you to compute relative azimuth for
the TruPulse 360. First the definitions:

**Let:**

P_{0} = location of the
measurer

P_{1} = location of
point #1

P_{2 }= location of
point #2

D_{1} = horizontal
distance to P_{1} from P_{0} (one of the returns
of the TruPulse 360).

D_{2} = horizontal
distance to P_{2} from P_{0} (one of the returns
of the TruPulse 360).

D_{3} = horizontal
distance to P_{2} from P_{1} (one of the returns
of the TruPulse 360).

A_{1} = azimuth of P_{1}
from P_{0} (one of the returns of the TruPulse 360).

A_{2 }= azimuth of P_{2}
from P_{0 }(one of the returns of the TruPulse 360).

A = azimuth of P_{2}
relative to P_{1}.

Case I:
/A_{2}-A_{1}/ < 180 degrees

A = 180 + A_{1} - A_{5}

Case II:
/A_{2}-A_{1}/ > 180

A = 180 + A_{1} + A_{5}

Case III:
/A_{2}-A_{1}/=180

A = 180+ A_{1}

I suppose one must really want to know if the relative azimuth
feature works on the 360 to go through the above process, but it
is what ENTS does.

Bob