Roundwood measurement of truck loads by laser scanning
A field study at Arauco pulp mill Nueva Aldea
Mats Nylinder1, Tonny Kubénka2, Mikael Hultnäs1
1
Swedish University of Agricultural Sciences, Uppsala, Sweden; 2Wood Measuring Society Qbera, Falun, Sweden
In Chile, Brazil and other countries in South
America systems for automatic scanning of trucks
to determine the volume of wood have been used
for several years. This system is based on laser
scanning and advanced mathematical algorithms to
calculate the volume. One manufacturer of such
systems is Woodtech of Chile, with its’ Logmeter
4000 system. The system is also used to determine
the volume for chips and coal (Anon 2008/1).
Laser scanning of individual logs is used in many
sawmills and is a well known technique
(Björklund, L., 2003, Edlund, J., 2004). Scanning
of whole trucks to determine the volume of wood
is done in some places in Finland and Sweden but
it is not as established as in South America (Anon
2006/2, Huttunen, T., 2006, Marjomaa, J. &
Sairanen, P. 1996, Moilanen, P., 2003 Nylinder,
M., 1992). The purpose of this study is to compare
the manual measurement of pulpwood used in
Sweden with automatic laser scanning of
truckloads to try to develop a more efficient way of
measuring wood for Scandinavian conditions.
Introduction
In the pulp industry in Sweden the wood raw
material represents about 50% of the total cost of
production and in the sawmill industry about 70%.
Considering that this is a large proportion of the
total cost, relatively few resources are put into the
development of new systems for measurement the
quantity and quality of incoming wood. Today in
Sweden most of the pulpwood is measured when it
arrives at the pulp mills. The trucks arrive at the
measuring station where each pile of wood is
measured manually with a stick by scaling its
height, length and width. The solid volume content
under bark is then visually estimated. The wood is
also graded with respect to species, dimension, rot,
reject etc. To continuously check and control the
measuring, samples are taken for manual log by
log measuring and determination of solid volume
under bark. This sample measuring is, for some
methods, also used to adjust the original
measurement. For the measuring of samples a new
automatic technique is under development (Anon
2008/2).
Material and methods
The study was carried out in November 2008 at the
Arauco Nueva Aldea pulp mill in the region of Bio
Bio in Chile. Logs of eucalyptus (Eucalyptus
globulus) pulpwood were sorted in three dimension
classes: large, medium and small. The goal was to
get at least a truck pile of logs of each dimension
class. The logs were manually debarked. Each log
in each dimension class was manually measured
with a calliper and a ruler for its diameter and
length. The diameter measurements were taken 10
cm from the top end, in the middle of the log and
10 cm from the butt end. The length was recorded.
For logs which were noted as butt logs, the
diameter was measured 50 cm from the butt end.
All logs were numbered to facilitate the
identification if some measures were falsely
recorded. After this measurement, 26 randomly
chosen logs of each dimension class were
measured once more to determine the accuracy and
repeatability of the manual measurement.
Pulpwood is graded in many countries by its
weight, green or dry. The problem with this
method is the variation in its moisture content and
the technique to determine moisture content is still
very costly and time consuming. Over time several
investigations have been performed regarding
possibilities of changing today’s pulpwood volume
measuring system, with prospects of replacing it
with weighing the pulpwood and determining its
moisture content, e.g. (Björklund, L., 1988),
Thygesen, L., 1996 and Hultnäs, M., 2008).
In Scandinavia forest growth, standing volume and
cost for harvesting is related to volume, not weight,
and although a system for weight is used there is a
need for quantities in volume. This means that it is
of great interest to develop systems to have a lower
cost and more efficient system to determine the
volume. Volume in combination with weight is
probably the overall best system as this will also
give information of density and the freshness of
wood.
The diameters were recorded in cm classes, values
within a cm range were recorded as class bottom,
1
e.g. a log that had the actual diameter 10.6 cm was
recorded as 10 cm in the protocol. For the volume
calculation half a cm was added to the recorded
value. The length measurement was recorded in dm
at class bottom. When calculating the volume, five
centimetres were added to the recorded volume.
The volume of the logs was calculated in two
ways:
A: Mid-diameter. (Huber’s formula) Based on the
mid-diameter and length.
The following formula was applied:
Va =
 Dm 2
1
×π × 
100000
 4

× L

(1)
Va = Volume in m3
Dm = Mid-diameter in cm
L = Log length in dm
B: Top-butt-diameter. Based on top and butt
diameters. The volume calculation is based on a
model developed for Swedish roundwood, mainly
Scots pine (Pinus silvestris) and Norway spruce
(Picea abies) but also for birch and other
hardwoods. (Anon 2000)
Figure 1. Woodtech’s Logmeter 4000. Laser-scanners are
circled in yellow.
laser-scanning system (Anon 2008/1). The piles
were then rearranged or switched with another pile
and measured again in the same way.
The following formula was applied:
(
2
2
π 
Va = 100000 ×   × L × α × ( Db ) + (1 − α ) × ( Dt )
4
)
The manual measurement of the piles was carried
out according to a method developed for Swedish
pulpwood and Swedish conditions. In this method
frame volume of the pile is measured by a scaler
while standing on a scaling bridge at the same level
as the pile. In the study, this was done at ground
level. To estimate the solid volume content, a
standard value for the specific wood species is
used, and then adjusted by the estimation of
diameter, stacking quality, straightness, delimbing
quality, bark content, taper etc (Kubénka, T.,
2008).
(2)
Va = Volume in m3
Dt = Diameter in top end in cm
Db = Diameter in butt end in cm
L = Log length in dm
α = Constant according to Table 1
Table 1. The constant α
Diameter top
(cm)
-349
Length (cm)
350-449
450+
-14
0.485
0.485
0.485
15-24
0.465
0.460
0.455
The roundwood truck measurement was done by
laser scanning the periphery of the load from both
sides and from above, with the Logmeter 4000.
The truck is driven through the system at a fairly
constant and low speed to get as good raw data as
possible. Using the information generated,
Woodtech has developed algorithms to estimate
length, diameter, stack volume and solid volume.
As pulpwood trucks in South America seldom have
truck-mounted cranes, algorithms for the cranes are
not yet fully developed. Due to this, the influence
The logs were loaded pile-wise on a truck for
pulpwood. After a pile was loaded on the truck and
on the trailer, stack volume and solid volume
content of the pile were manually estimated. After
the manual measurement the truck drove to the
Logmeter, Figure 1, where it was measured by the
2
of the crane was manually adjusted before all the
laser data was presented.
Diameters
Next, each cross-section of the load is analyzed,
determining the best fit for the diameter of each
periphery log. This is replicated throughout the
load, leading to the identification of all exterior
logs.
Woodtech, who developed the scanning system,
describes the equipment as follows: ”Logmeter
4000 is the most advanced laser-scanner system
available for the scaling of wood loads. The
measurement process is simple and automatic, with
human intervention in less than 5% of cases. The
scanning process takes less than a minute, which
allows more than 600 trucks to be scanned per day.
The system can measure different configurations,
including fixed and variable length, tree-length,
chip and forest residue loads.
Scanning
As the truck enters the measurement area, high
precision laser-scanners sweep the truck,
generating hundreds of cross-sections of the load
and creating a 3D representation with more than 1
million individual measurements.
Figure 4. Principle for automatic identification of periphery
logs.
Biometrics
With each log of the periphery modelled in space,
the system then calculates the biometric
information of the log, including diameter, length,
taper, and crook.
Figure 2. Principle for 3-D Interface for log identification.
Segmentation
Using image processing algorithms, the limits of
the load are identified and the unwanted elements,
such as truck wheels, drawbars, and platform, are
eliminated.
Figure 5. Principle for individualization of periphery logs
and identification of biometric characteristics.
Solid volume
In the final step of the process, the solid volume is
calculated. This is done using mathematical models
which are calibrated for each specific site where a
Logmeter is installed. The model determines the
relationship between the parameters calculated for
the periphery of the load and the total volume. The
model can be easily updated over time, thus
ensuring precision.
Generated results include volume, diameter, and
length classes for each bundle of logs. All results
and images are stored in the mill’s administrative
system. The system allows for trucks to be first
measured and then calculated at different moments
Figure 3. Principle for automatic segmentation of the load.
3
Table 2. The amount of measurements
Pile
Number of logs
Number of pile
measurements on trailer
Number of pile
measurements on truck
Blue, small dimension
132
1
3
Green, medium dimension
Red, large dimension
118
102
3
3
3
1
Table 3. Description of the logs and piles
in time. This is useful for reducing truck lines and
even allows for unmanned operation. The
Logmeter includes a powerful auditing system
which allows all data to be reviewed at a later date,
even permitting electronic re-measurements if
necessary. This maximizes the transparency and
traceability of the measurement process. Results
can also be shared by Internet with suppliers,
management, and government” (Anon, 2008/1).
Variable
Pile
Blue
Green
Red
132
118
102
Amount of butt logs (%)
17
29
44
Middle diameter (cm)
Average
Std
9.2
2.4
13.2
2.1
16.5
2.4
Length (dm)
Average
Std
56.1
8.5
57.3
8.1
57.0
7.9
Taper, (mm/m)
Average
Std
5.5
1.99
5.2
1.95
4.8
2.07
0.045
0.024
5.877
0.080
0.029
9.484
0.133
0.041
13.587
Volume, ”top/but diam.” (m3)
Average
0.046
Std
0.024
0.083
0.032
0.138
0.043
Number of logs
The last part of the study was a study of
repeatability with the laser-scanner. The truck and
trailer were driven ten times through the Logmeter
without rearranging the load.
For the analysis of the results, standard formulas
for mean and standard deviation were used. The
correlation between two variables reflects the
degree to which the variables are related. In this
paper we have used the Pearson Product Moment
Correlation (Yamane, T., 1969).
Volume, ”mid diam.” (m3)
Average
Std
Total
Result
The characteristics of the logs according to the
manual log by log measurement are described in
Table 3. After the original measurement, 26 logs
from each pile were randomly sampled and
measured once more. The result of this
measurement was compared with the first original
measurement.
Table 4. Result of manual control measurement of 26 logs
per pile
Method for volume
measurement
Table 4 shows the control measurement minus the
original measurement and the standard deviation of
the difference.
Of the four blue piles, three piles were on the truck
4
Pile/Stack
Blue
Green
Red
Volume mid, (m3)
Mean of diff. (m3)
Mean diff. (%)
Std for diff. (m3)
1.2832
-0.0027
0.21
0.0055
2.1714
0.0011
0.05
0.0047
3.4682
-0.0007
0.02
0.0057
Volume top/but, (m3)
Mean of diff. (m3)
Mean diff. (%)
1.3118
-0.0005
0.04
2.2572
-0.0009
0.05
3.6583
-0.0014
0.04
Diameter laser/diameter log-by-log r2 = 96.9%, P =
0.000, F = 374
and one pile was on the trailer. Three of the green
piles were on the truck and three were on the
trailer. One of the red piles was on the truck and
three were the trailer. The estimation of diameter
and length is given in Table 5 and the estimation of
solid volume in Table 6.The correlation between
the two methods is:
Length laser/ length log-by-log r2 = 35.2%, P =
0.025, F = 6
Table 5. Recorded diameter and length by the laser and log-by-log measurement
Stack
Trailer/
Truck
Load
No
Diam.
Laser
(cm)
Blue
Trailer
Truck
Truck
Truck
1
1
2
3
11.3
10.9
10.4
10.8
10.9
0.32
9.2
9.2
9.2
9.2
9.2
54.8
56.1
54.1
51.1
54.0
2.12
56.1
56.1
56.1
56.1
56.1
Trailer
Trailer
Trailer
Truck
Truck
Truck
1
2
3
1
2
3
13.4
13.5
13.1
14.2
13.5
13.5
13.5
0.37
13.2
13.2
13.2
13.2
13.2
13.2
13.2
58.4
57.9
57.4
56.6
53.4
57.3
56.8
1.79
57.3
57.3
57.3
57.3
57.3
57.3
57.3
Trailer
Trailer
Trailer
Truck
1
2
3
1
16.5
17.0
16.6
16.8
16.7
0.22
16.5
16.5
16.5
16.5
16.5
58.4
58.7
58.6
55.7
57.9
1.44
57.0
57.0
57.0
57.0
57.0
Mean
Std
Green
Mean
Std
Red
Mean
Std
Diam.
Log-by-log
(cm)
Length,
Laser
(dm)
Length,
Log-by-log
(dm)
Table 6. Manual and laser determination of solid volume for the piles
Stack
Trailer/
Truck
Load
No
Laser
3
(m )
Log-by-log
3
(m )
Manual,
Stack estim.
3
(m )
Diff. Laser,
Log-by-log
(%)
Blue
Trailer
Truck
Truck
Truck
1
1
2
3
6.05
6.10
6.20
6.02
6.09
0.08
6.09
6.09
6.09
6.09
5.66
6.33
6.63
6.17
6.18
0.41
-0.7
0.2
1.8
-1.0
0.1
1.3
6.4
-3.8
-6.9
-2.5
-1.7
5.7
Trailer
Trailer
Trailer
Truck
Truck
Truck
1
2
3
1
2
3
9.75
9.43
9.50
9.99
9.75
9.95
9.73
0.22
9.85
9.85
9.85
9.85
9.85
9.85
9.33
9.66
9.86
9.98
10.80
10.42
10.01
0.53
-1.0
-4.4
-3.7
1.4
-1.0
1.0
-1.3
2.4
4.3
-2.4
-3.7
0.1
-10.8
-4.7
-2.9
5.0
Trailer
Trailer
Trailer
Truck
1
2
3
1
13.08
14.03
13.30
13.59
13.50
0.40
14.05
14.05
14.05
14.05
13.57
14.62
14.04
14.31
14.14
0.45
-7.4
-0.1
-5.6
-3.4
-4.2
3.1
-3.7
-4.2
-5.6
-5.3
-4.7
1.0
Mean
Std
Green
Mean
Std
Red
Mean
Std
5
Diff. Laser
Manual
(%)
Figure 7. Relationship between manual and laser-scanner estimation (left) and between log by log and laser-scanner
estimation (right) of solid volume.
Table 7. Manual and laser determination of stacked volume
Stack
Trailer/
Truck
Load
No
Laser
3
(m )
Manual
3
(m )
Blue
Trailer
Truck
Truck
Truck
1
1
2
3
11.12
11.78
11.48
12.56
11.74
0.61
10.89
11.94
13.82
12.35
12.25
1.05
2.0
-1.4
-20.4
1.7
-4.5
10.6
Trailer
Trailer
Trailer
Truck
Truck
Truck
1
2
3
1
2
3
17.04
16.62
17.83
16.92
18.78
18.52
17.62
0.90
15.55
16.95
16.99
16.63
19.64
18.28
17.34
1.43
8.7
-2.0
4.7
1.7
-4.6
1.3
1.7
4.7
Trailer
Trailer
Trailer
Truck
1
2
3
1
22.13
24.87
22.6
21.42
22.76
1.49
20.87
23.97
21.94
22.35
22.28
1.29
5.7
3.6
2.9
-4.3
2.0
4.3
Mean
Std
Green
Mean
Std
Red
Mean
Std
Diff. Laser-Manual
(%)
The correlation between
estimation were for:
Solid volume , laser/manual
0.000, F = 926
laser
and
manual
r2 = 98.7%, P =
Solid volume, laser/ log by log r2 = 99.2%, P =
0.000, F = 1553
Stacked volume, laser/manual r2 = 95.1%, P =
0.000, F = 232
A measure of the stacking in the piles is the solid
volume percent, the solid volume in relation to the
stack volume, Table 8.
Figure 8. Relationship between manual and laser-scanner
measurement of stacked volume.
6
Table 8. Estimation of solid volume percentage
Number of obs.
Mean laser (%)
3)
Std (m
Mean, manual (%)
Std
Blue
4
52
3.0
51
2.2
Green
6
55
2.8
58
1.9
Red
4
59
2.9
64
1.7
At the end of the study the trailer and truck were
scanned 10 times with the laser without rearranging
the piles between each measurement.
Table 9. Result from ten independent measurements of the
blue and red piles without rearrangement of the load
Statistics
Diam.
(cm)
Length
(dm)
11.6
0.31
55.6
1.38
11.24
0.30
6.1
0.14
16.6
0.29
56.8
0.56
21.7
0.21
13.7
0.21
Blue pile, trailer
Mean
Std
Red pile, truck
Mean
Std
Figure 9. Example of end cracks.
Stack
Solid
3
3
vol. (m ) vol. (m )
Discussion
The log by log measurement is supposed to yield
the ”true” volume not including whorls or sections
were the diameter is increasing from butt to top
end. Some butt logs were also shortening due to
quite large fell combs. Quite a few logs were split
and had cracks and the diameters were taken in a
way trying to disregard these defects.
Figure 10. Crack along the log.
The way of calculating the volume by the top/butt
method is also based on formulas developed for
Swedish conditions and not for eucalyptus. The
debarking of the logs was not 100% perfect and
compared to bark on pine and spruce in Sweden
the eucalyptus bark has more strips in the
longitudinal direction which probably makes it
more difficult to measure precisely disregarding
the bark which was left. The cracks and splits,
bark and fell combs will of course for both the
manual and the laser scanning generate errors.
Figure 11. Example of fell comb.
The arithmetic mid diameter for the small
dimension wood was recorded in the manual
measurement as 9.6 cm, which is less than the
average diameter for spruce pulpwood in Sweden,
which is about 11-12 cm. The average diameter
for softwood and birch pulpwood in Sweden is
about 13 cm (Statistics, VMF Qbera). This
means that the medium class in this study,
green, has about the same average diameter as
Figure 12. Logs before loading on truck and trailer.
7
Swedish pulpwood. The manually measured length
of the wood was recorded at about 57 dm which
compared to random length pulpwood in Sweden is
at least 10 dm longer. The taper was measured to
be about 5 to 6 mm/m. The taper for pine and
spruce pulpwood in Sweden is normally a bit more.
measuring and that the logs are not ”perfect” one
cannot say which is the correct diameter, length
and volume. In Table 7 the solid volume estimated
for piles on the trailer and truck is given. The laser
scanning gives between 0 to 4% less volume than
the log by log measurement. Compared with the
manual estimation the laser gives 1.5% less volume
for the small dimension and 3% resp. 5% less
volume for the green and blue pile. The correlation,
r2 = 99%, between the two methods is very good
and significant which indicates a potential that the
methods can be calibrated to each other. The
correlation between the laser-scanning and log by
log measurement is also significant and strong,
with r2 = 99%.
The two manual methods to calculate volume of
the logs yield about the same volume and the
control measurement indicates that the manual log
by log measurement has a good repeatability. One
must however mention that the repeatability
measurement was done by the same persons and
other persons measuring the same logs will
probably give other results. Another factor that can
influence the log by log measuring is weather
conditions. The logs themselves are also a factor
since it is probably easier to get a stable and correct
manual log measurement on large dimension logs
which are properly debarked and of same length
compared to small crooked and cracked logs.
The laser-scanning for the small dimension
calculates a smaller stacked volume compared to
the manual estimation, by about 5%. For the green
and red piles the laser scanning gives a 2% larger
volume. One observation has a difference of 20%
which is difficult to explain but could be a
registration error. The correlation between the two
methods is very strong r2 = 95%, but not as
significant as for the solid volume.
The estimated log diameter by the laser-scanner
measurement was for the blue logs 10.9 cm
compared to the manual measurement which gave
9.2 cm. For the green pile, the corresponding
values were 13.5 for the laser-scanner and 13.2 for
the manual measurement and for the red pile, 16.7
cm and 16.5 cm respectively. For the medium and
large dimension logs, the diameter is almost the
same for the two methods. For the small dimension
logs the difference is about 10%. The correlation
between the two methods, r2 = 97% is however
strong and the relation is significant which
indicates that it has a good potential for calibrating.
An exact figure on diameter is often of less
importance – it is normally a rough value which
can be of interest for pricing and sorting of wood in
Scandinavia
When looking at precision and exactness it should
be seen in relation to the stack volume of the piles.
A large volume, such as for the red piles (22 m3),
means that a smaller proportion of the logs of the
pile are directly scanned by the laser in comparison
to the case of the small blue pile (12 m3).
The ten repeatability measurements of the small
dimension logs indicate a very good repeatability
of the laser-scanning method. This is as always a
very strong side of a mechanical automatic method
compared to a manual measurement. As the laserscanner has a high repeatability, it has a high
potential to be adjusted to different methods used
by different mills and standards existing in
different countries. The scanning is very fast (<1
minute per truck) and the volume measurement,
both stack and solid, can be rationalized compared
to most manual methods. An efficient system in the
first step of the measurement makes it possible to
put more resources into sampling piles for control
and adjustment if needed.
The measured log length by ruler was 56.1 dm for
the blue, 57.3 dm for the green and 57.0 dm for the
red. Corresponding figures recorded by the laserscanner were 54.0 dm for the blue, 56.8 dm for the
green and 57.9 dm for the red. The difference is 1
to 2 dm. The correlation between manual
measurement and laser-scanner estimation of
length is not that strong (r2 = 35%) as for diameter
but can probably also be calibrated and as for
diameter the need of a very exact value is normally
of less interest.
One can also, if needed, put more resources into
measurement of rot, defects and bark if the volume
can be measured very efficiently. Combining the
laser scanning with weight measuring, which
Due to the different definition and ways of
8
should be easy, will create a system which also
gives an indication of the density and freshness of
the wood. For Swedish conditions it is also
important to develop the system to allow for
multiple deliveries within a pile and for the
influence of snow and ice in the winter*. As
Sweden measures the volume under bark, a
scanning system based on lasers also has to be
combined with some type of estimation of bark
content. The bark can perhaps be taken in
consideration in a similar way as it is done in the
automatic new log by log laser scanning for sample
bundles of pulpwood in Sweden. In this system,
dimension and amount of butt logs and a visual
estimation is used to covert measuring on bark to
under bark (Björklund, L. 2004). The trucks in
Sweden also normally have cranes and that makes
it important to develop an automatic way to sort
out the influence of the crane on the truck pile**.
Anon
2008/2.
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Mobil
automatisk
stickprovsmätning,
produktblad.
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redovisning.SDC, Sundsvall.
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virkesmätning och redovisning, Uppsala.
Edlund, J. 2004. Methods for Automatic Grading
of Saw Logs. Doctoral Thesis , Acta
Universitatis Agriculturae Sueciae, Swedish
University of Agricultural Sciences, Uppsala.
Hultnäs, M., 2008. Methods for the determination
of the dry matter content of roundwood
deliveries. 2008.
Huttunen, T., 2006. Abstract, Measuring of Bast
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Compared to manual measurement, automatic measurement has a potential to be very stable with a
good repeatability and can be calibrated to
different standards. Manual methods are always
related to the individual person so it will often be
more difficult to get the same measurement for all
scalers, conditions and mills.
(*) Woodtech has experience through a partnership in
Scandinavia of the use of a simple roof structure to protect
the system from extreme weather conditions.
(**) During the first half of 2009 Woodtech has developed
the necessary algorithms to solve the effect of the crane.
Literature list
Anon
2000. Kompendium i virkesmätning.
Virkesmätningsrådet, SDC, Sundvall.
Anon 2006/1. Measuring rules for pulpwood.
Recommended by The Swedish Timber
Measurement
Council
Swedish
Timber
Measurement Council VMR 1-06 Measuring
rules for of pulpwood.
Anon 2006/2. Protokoll från Jord- skogsbruksministeriets förorning om rambildsmätning av
virke med lasersaknning. Förordning Nr 66/06.
Helsinki.
Anon 2007. Arauco, Annual report 2007, Arauco,
Santiago, Chile.
Anon 2008/1. Woodtech measurement solutions,
Inforamtion material www.woodtechms.com,
Santiago, Chile.
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