noise. The presented method complies with theoretical 
expectations; only one tree shows a different behaviour 
(continuous decrease of the number of filled voxels). 
  
  
  
  
  
  
  
  
  
  
  
DBH DBH Diff. Height Height Diff. 
Tree | contr. estim. [cm] contr. | estim. ie 
[m] [m] [m] | [m] 
Al 0.41 0.42 - 0.01 15.3 14.8 +05 
A2 0.44 0.42 +002} 155 14.9 + 0.6 
A3 0.38 0.38 0.00 | 12.6 119 +07 
C1 0.25 0.26 - 0.01 14.7 13.4 +1.3 
RI 037 0.37 0.00 | 10.4 9.9 OS 
R2 0.73 0.65 +0031 187 17.9 +0.8 
Bl 0.42 0.42 0.00 --- 14.1 --- 
TI 0.42 0.41 * 0.01 11.6 10.0 251.6 
T2 0.33 0.32 t 0.01 10.6 10.6 0.0 
  
  
  
  
  
  
  
  
Table 2. Estimated and control DBH and tree heights 
In addition to tree volume, DBH and the height of trees — often 
used as variables for biomass functions — are calculated (Table 
2). Estimates of DBH correspond to the measured control 
values with only marginal deviations (with one exception). For 
all trees, height determination is systematically lower than 
related manual measurements. Approximately, the differences 
lie between 0.5m and 1.5m caused by the uncertain acquisition 
of the highest part of crowns from terrestrial position — by TLS 
as well as by manual measurement. 
6. CONCLUSIONS 
The presented method delivers good results in accordance with 
the control data. It was found to be more accurate than other 
methods such as detailed analysis of aerial images or 
measurement of main branch perimeters by specialists climbing 
the trees and predicting the connected branch volumes. The 
usage of a voxel structure, the noise suppression and the 
processing of the data 1n horizontal layers leads to a significant 
data reduction and enables the processing of large data sets 
consisting of 20 to 60 million points. The applied extended 
algorithm for filling hollow surfaces is generally applicable for 
stems as well as for complex crowns. The advantages of this 
method are its simplicity and robustness, ie. no complex 
Skeleton extraction or fitting of cylinders is necessary. 
Moreover, volume extraction is independent of branch length, 
diameter or orientation. It needs no advanced input information 
and can be used for a wide range of applications. The 
drawbacks of this approach are the necessity of high resolution 
scans and the extensive computing time for determination of a 
suitable threshold for noise reduction. In future studies, it is 
suggested that the number of analysed trees be increased to 
obtain a better statistical basis, to allow extrapolation to larger 
areas. Additionally, further investigations have to be carried out 
concerning the influence of the number and position of 
necessary scans, possibly in dependence on the tree structure. 
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