Native Tree Society BBS

ENTS,

Of late, I've resumed testing the TruPoint 300 as I promised LTI I would do. The attachment shows the TruPoint's accuracy for trunk diameter measurements as of 10 trials. As the number of trials expands, I don't expect the average difference between caliper and TruPoint measurements to stay so close as now, but I will be surprised if the average difference exceeds 0.25 inches for trunks with diameters up to 36 inches - the limits of my calipers for comparison.

To use the TruPoint for diameter measuring to the best result, several internal functions must be used: (1) Missing Line routine to measure any trunk lean in degrees from either the horizontal or vertical axes, (2) the distance from the TruPoint to the middle of the trunk on the diameter line being measured, and (3) the Diameter routine, itself. I've included an adjustment if the instrument is too close to the trunk so that the edges of the trunk are not visible.

I've also created an Excel workbook to do a complete trunk modeling using the TruPoint 300. I will need to modify it a bit to incorporate the adjustment for being too close, but it is basically finished. Now to put it to use.

Oh yes, LTI has reduced the TruPoint's price to $1,300. BTW, it is advertised as a total station instrument. It is also called a mini-surveying station. Its class 2, phase-based laser has a rated accuracy of +/-1.0 mm to a clear target, and +/-2.0 with less favorable visibility. With favorable conditions the range is to 1,000 feet. For trunk measurements, the working range is likely to be from about 25 to 150 feet.

Bob

Ents,

The testing of the TruPoint 300 Diameter function continues. My 300, which I affectionately have named YODA is performing extremely well.
The attachment tells the story.

Bob

Ents,

Steve Colburn recently informed Cadre members that LTI has secondhand TruPoint 300 units available for $875/unit. New ones now cost $1,300. The used price is truly a good value if you can make use of the versatility of the instrument. But what might that mean for tree-measurers?

The 300 is advertised by LTI as a Total Station instrument. It has also been described as a mini-surveying station.Take your pick. I received my 300 back in Sept 2018 free under the understanding that I would field test the unit for LTI, which has been an on-going project. Since the 300 has a phase-based red beam laser instead of an infrared pulse-based laser, its utility to tree measuring has not always been clear. You would still need an infra-red laser unit for traditional height measuring. However, six functions of the 300 are undeniably valuable to us:

1. Measuring single distance (conventional laser rangefinder return)
2. Height-profiling measurement (height above a base position at points up a trunk)
3. Missing Line (this is a 3-dimensional capability)
4. Diameter (this routine assumes the trunk is circular)
5. Height tracking (Allows you to move up a vertical target and get continuous height readings)
6. Smart horizontal mode (This is actually a sine-based measuring capability. You get the target's vertical height, horizontal distances and angle)

There are a couple of other functions that could have value in more advanced measuring projects. One that I plan to test is

7. Triangular area
8. Smart Angle (this is a dihedral angle measuring capability)

There is an iPhone app for controlling the 300 from the iPhone and for downloading certain categories of measurement results to a computer. The process is rather involved and as of now, I'm not sold on it. Just too many steps required.

The attached Excel workbook give a routine to measure the volume of a frustum. It can be extended to measure the volumes of adjacent frustums to return a trunk volume. The method compensates for trunk lean. It also helps the measurer estimate the missing part of the diameter if too close to the trunk. A second worksheet shows the comparison of the diameter routine against caliper measurements. This is an on-going evaluation, and I expect the average difference between calipers and the TP 300 diameter routine will not exceed +/-0.3 inches, although for clear, fairly close targets, the average difference will be more on the order of +/-0.2 inches.

Understand the true accuracy of the 300's laser, tilt sensor, and compass across a range of conditions is not easy. However, overall the instrument has unbeatable accuracy for the cost.

I'll close with this. I seem to have a need to name all my instruments. My 300 is named Yoda - the force goes with it.

Stay safe, everyone

Bob

Ents,

I just sent a 10-page report to LTI on the diameter routine of the TruPoint 300. It is attached for any one interested.

Bob