General discussions of measurement techniques and the results of testing of techniques and equipment.

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Re: rounding

Post by mdvaden » Tue Dec 11, 2018 3:28 pm

dbhguru wrote:NTS,

This is a useful discussion to have because there is no single answer on when to apply rounding rules, and to what degree. The answer is case dependent on:

1. Accuracy of equipment being used and the state of its calibration
2. Expertise of measurer
3. Distinctness of target
4. Tripod or no tripod
5. Amount of effort put into verifying measurements (very, very important)
6. Method of measurement (sine vs tangent)
7. Situation involving measurement (championship status, scientific paper, general article, our database, etc.)
8. To whom a measurement is being reported

In the case of champion tree reporting, rounding to the nearest foot, probably rounding down, makes sense today. In the future, as more candidates are certified by National Cadre members, rounding down to the nearest half-foot may be justifiable, and even to a tenth in certain circumstances. Regardless, It would be useful to include a range. For example, if the target is distinct, and I take my time, I can confidently state an accuracy to +/- 0.5 feet with the TruPulse 360. I have repeatedly tested this instrument and obtained an accuracy range of between +/- 0.25 and 0.3 feet when recording at the point of changeover on the display and using a tripod. The TruPulse 200X is accurate to +/- 1.5 inches as tested against industrial red beam lasers accurate to +/- 1.5 millimeters. Interestingly, my Nikon Forestry Pro is pretty darned accurate as well. Here is a just completed comparison between the three instruments for distance.
Note that comparison of straight averages doesn't tell the story. The average of the absolute differences between two instruments is the operative comparison, Note how close the two TruPulses are. Their maximum difference is 0.5 feet and the average is 0.24. To my surprise, the overall performance of the Nikon is quite good, but it hiccups every now and then, and the greater distance tend to be most problematic, although not always.

Note that these numbers do not mean that in height calculations, the three instruments will yield averages that are as close as the above. For height, as opposed to simple distance, we must take into account the returns of the tilt sensors. In the next calibration tests, I'll show some results on the angles, and then put distance and angle together. At that point, we can get into the finer points of when we should call for rounding to a particular level and for what purpose. Lots to discuss. Hopefully, others will contribute, e.g. Michael Taylor.

As a final point, measurers like Michel Taylor and Will Blozan seem to have accuracy meters built into their heads. If they report a measurement to a tenth of foot, I would be reluctant to expect them to round in any direction. I would accept reporting to the tenth of foot. However, for less experienced measurers, rounding down to the whole foot makes sense, especially at the level of reporting for champion tree competitions where rules are needed.


I just posted in general discussion about Trupulse 360 accuracy, and apparently no replies. Hard to believe nobody knows, so I tried the search feature and burrowing old posts. In this older posting of yours, were you shooting with a remote trigger or your finger when you managed that approximate plus or minus 1/4 to 1/3 ft. accuracy?

Its the same laser used this late 2018 on Centurion Eucalyptus and they guys apparently used finger push on button, without prisms. Maybe upwards of 20 measures all added together, some aiming for bark patters and marks on the tree.

Trying to get an idea of how the laser itself fits within that process.


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