Verfahren zur einzelstammweisen Volumen - Forstliche Versuchs

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simulating a mechanical calliper (calliper diameter). In the other, the measurement of log
diameters was based on the real contour of a cross section (contour diameter). As expected,
the results show that in direct comparison, the measured values of the contour diameter are
always at least as big as those produced in an identical measurement plane using the
calliper diameter. On average, the simulation of a mechanical calliper leads to an
overestimation of 1.6 mm in diameter.
With respect to the determination of diameters, rounding, which is established in forest
practice and carried out according to forest guidelines (Forst-HKS), plays an important role.
Rounding has its origin in the manual measurement. Diameters are unilaterally rounded
down. This is also applied in the practice of electronic measurement and leads to an
underestimation of the volume of nearly 3 % compared to the volume calculated using
unrounded diameters.
In this investigation the determination of the log length is irrelevant, as the available raw
data allows a clear determination of the measured stem length and consequently, a
calculation of payroll-related length is guaranteed. Therefore, volume differences between
different methods are not caused by different log lengths. All volumes have been calculated
on the basis of uniform log lengths.
For the determination of log volume, principally different approaches were implemented:
1. Determination of the log volume on the basis of calculating a cylinder volume using
an ordinary mid-diameter;
2. Determination of the log volume by dividing the log into sections of equal length,
with the log volume as sum of all individual section volumes (cylinders);
3. Determination of a reference volume, which is calculated using all available data
points and thus approximates the real physical volume of the log.
In contrast to the different cylinder and section volumes, the reference volume is not
calculated on the basis of one or few diameters, but on the basis of the real contour of a
cross section.
Based on the results obtained by the simulation of different measurement methods, it can
be shown how various approaches of determining diameter and volume influence the
measurements results.
Consequently, currently applied methods such as the measurement according to the
regulations established in Germany (Rahmenvereinbarung Werksvermessung) as well as in
Austria (ÖNORM L1021), are simulated on the basis of a common data base. In addition,
alternative potential methods for volume determination were demonstrated and also
simulated based on the available data set. The results of the simulation show that different
methods for determining the volume do indeed have a relevant impact on the measurement
results. The calculation of the log volume on the basis of a cylinder leads to an
underestimation of the volume when compared to the reference volume (mean relative
difference). There is a difference of about 3 % between the methods applied in Germany
(Rahmenvereinbarung Werksvermessung) and Austria (ÖNORM L1021) referring the
volume. The determination of the volume according to the ÖNORM tends to result in an
underestimation of the volume compared to the volume determined according to the
German guidelines. In addition to the quantitative comparison of the different methods