**3. Ways of dimension scanning**

Measurements and methods of their implementation are given by the need of data on wood (in which moment, type of data and satisfactory accuracy) and by the technical and practical feasibility of measurements.

According to the type of manufacture determined for the wood, mass measurements of logs are sufficient (production of agglomerated materials, paper, and cellulose) or it is necessary to measure parameters of particular logs separately (production of sawn wood, veneers). At mass measurements, a basic parameter consists in the total volume of supply; extents of the diameter and length of logs are usually only completive data. Volumes, dimensions and often even the number of particular logs are not recorded at these types of production because they are not decisive.

measurement and reception of timber. It stems from the author's survey of using sensing and evaluation systems in the Czech Republic and literature data on these problems in

In the analytical and result part, a general algorithm is derived of processing sensed data. Steps are determined leading to different results of particular regulations. The results are compared with results of a method, which tries to evaluate the volume of logs (closest to the geometrical volume) from data taken by systems used at present. In relation to the volume

At the end, the paper indicates directions for the further progress of research and agreements as well as legislative regulations with a view to minimize differences in the

Dimensions and volume of wood together with its quality are basic data accompanying wood from the stage of a young stand until the end of the wood product service life. In many cases, it is sufficient to know only approximate values of dimensions and volume, e.g. growing stock, the volume of cut, and roundwood supplies on log yards. On the other hand, operations controlling production or where wood is the subject of business – goods, are

The tree stem or its part, log, is a body, the form of which is mostly compared to a truncated cone, paraboloid or cylinder. However the real form does not correspond to any regular geometric body. Moreover, it is affected by considerable individual diversity given by the tree species, tree age, site, tree position in the stand, care of the stand, type and extent of attack, mechanical damage either natural or caused by man activities and many other effects. From the aspect of dimensions, these effects become evident in various taper, sweep, flattening, root swelling, buttress, burrs and cracks. Production defects of wood are represented by remains of branches and damage to the stem surface at branching and handling, chamfer cuts, hinges (holding wood) after cutting or bucking (cross-cutting), cracks etc. All these properties have to be taken into account at stem or log measurements and at the evaluation of their dimensions and volume. Bark – its thickness and condition,

Measurements and methods of their implementation are given by the need of data on wood (in which moment, type of data and satisfactory accuracy) and by the technical and practical

According to the type of manufacture determined for the wood, mass measurements of logs are sufficient (production of agglomerated materials, paper, and cellulose) or it is necessary to measure parameters of particular logs separately (production of sawn wood, veneers). At mass measurements, a basic parameter consists in the total volume of supply; extents of the diameter and length of logs are usually only completive data. Volumes, dimensions and often even the number of particular logs are not recorded at these types of production

surrounding countries (mainly Austria, Germany and Slovakia).

measurement and determination of the volume of roundwood.

represents a separate problem at the measurement of wood.

**3. Ways of dimension scanning** 

feasibility of measurements.

because they are not decisive.

**2. Round wood** 

sensitive to accuracy.

determined in this way properties of existing procedures are also mentioned.

At the measurement of particular logs we need to obtain following data:


Dimensions and volumes of particular stems (logs) have to be known already in place of felling, at the latest in places of skidding before the wood haulage from forest (cut records, output of workers and their remuneration). If felling is carried out manually by one-man chain saws then means used for measurements are usually simplest, namely a calliper and tape.

Fig. 1. Electronic calliper with a tape.

*Manual measurement* and its unpretending equipment is quite satisfactory from the aspect of the accuracy of its results (units – cm) and possibilities to carry out subsequent cross-cutting tree-length logs. Values of diameter and length create, at the same time, basic data for records and calculations of volumes. It is usually determined according to tables. Thus, the

/generally/ the importance and number of log conversion depots declines). Scanning equipment for the log diameter and length is always part of the equipment. At scanning the log diameter, the number of taken values of the log diameter in one place of length, direction of scanning, accuracy and density of scanning in the course of length are essential. *One-directional way of scanning - 1D* takes the value of the log diameter in one, usually vertical direction. As for possible technical designs, measuring frames are used nearly

One-directional scanning is not able to record the log flattening and only very roughly the

Using 1D scanning devices for the purpose of electronic reception is, therefore, unsuitable

*Bi-directional measuring (2D)* is carried out by two systems perpendicular at each other and placed in one frame. It can be installed in such a way one scanning to proceed in vertical direction and the second scanning in horizontal direction or both measurements perpendicular at each other to proceed at an angle of 45° with respect to a horizontal level.

Fig. 3. The principle of scanning the log diameter by a one-directional scanning frame.

The substantial advantage of *2D* scanning consists in the better record of the measured log form and thus a possibility to calculate objective values of the log diameter in the place of measurement. The evaluation of stem curvature (sweep) is markedly more accurate. To calculate the log volume both methods of placing the sensing elements are equivalent. However, vertically and horizontally oriented sensors record flattening the measured logs better – a flattened log shows a tendency "to lie down flat" on the conveyer, i.e. vertically measured diameter shows a smaller value than a diameter measured horizontally. At systems oriented at an angle of 45° this difference disappears and both data approach the

exclusively. The principle of scanning indicates a scheme on Fig. 3.

and results are affected by relatively considerable errors.

average value of log diameter in a given place.

log curvature.

accuracy of the measurement of the diameter and length of tree-length logs in the field gives generally the accuracy of values of dimensions and volume of logs given on bills of delivery.

*Harvesters* are equipped with electronic (electromechanical) scanning systems. Attainable accuracy of the measurement is higher (units – mm). However, results of measurements are substantially dependent mainly on the pressure of particular parts of the scanning equipment (delimbing knives or feeding cylinders). Values of these parameters change continuously according to conditions of felling (tree species, dimensions, and season). Therefore, results of measurements at these systems have to be continuously checked and revised (even several times per shift).

The stem diameter is scanned according to the deviation of delimbing knives or the deviation of arms of feeding cylinders. At scanning by means of delimbing knives (see Fig. 2), the angle of the deviation of two knives which press the stem to the third stable knife is scanned (the third point necessary to define a circle and the subsequent calculation of its diameter). At the measurement by means of feeding cylinders the deviation of arms usually of 3 feeding cylinders is scanned. These cylinders press the stem with each other (3 points of a circle are obtained on principle according to the figure) or a couple of conical cylinders placed against each other (the diameter is scanned directly). The deviation of cylinders is usually scanned by an induction sensor or potentiometer. The stem length is scanned by a pinion (sprocket) pressed to the stem surface during its movement. Turning the pinion is sensed by an impulse generator. Scanning directly by feeding cylinders is not used because at high loading (stem start, delimbing), the slippage of cylinders occurs on the stem surface. Errors resulting from the different length of the stem surface curve and its length are negligible.

Fig. 2. Photo + scheme of scanning the stem diameter and length at harvesters (both figures according to Ponsse).

*Log yards* of forest enterprises and wood processors are equipped with cross-cutting-sorting carriages (all round cars) or lines. The equipment serves for the preparation of supplies of logs to manufacturing plants or for the preparation of logs according to requirements of subsequent production (With respect to the increasing proportion of harvester logging

accuracy of the measurement of the diameter and length of tree-length logs in the field gives generally the accuracy of values of dimensions and volume of logs given on bills of delivery. *Harvesters* are equipped with electronic (electromechanical) scanning systems. Attainable accuracy of the measurement is higher (units – mm). However, results of measurements are substantially dependent mainly on the pressure of particular parts of the scanning equipment (delimbing knives or feeding cylinders). Values of these parameters change continuously according to conditions of felling (tree species, dimensions, and season). Therefore, results of measurements at these systems have to be continuously checked and

The stem diameter is scanned according to the deviation of delimbing knives or the deviation of arms of feeding cylinders. At scanning by means of delimbing knives (see Fig. 2), the angle of the deviation of two knives which press the stem to the third stable knife is scanned (the third point necessary to define a circle and the subsequent calculation of its diameter). At the measurement by means of feeding cylinders the deviation of arms usually of 3 feeding cylinders is scanned. These cylinders press the stem with each other (3 points of a circle are obtained on principle according to the figure) or a couple of conical cylinders placed against each other (the diameter is scanned directly). The deviation of cylinders is usually scanned by an induction sensor or potentiometer. The stem length is scanned by a pinion (sprocket) pressed to the stem surface during its movement. Turning the pinion is sensed by an impulse generator. Scanning directly by feeding cylinders is not used because at high loading (stem start, delimbing), the slippage of cylinders occurs on the stem surface. Errors resulting from the different length of the stem surface curve and its length are

Fig. 2. Photo + scheme of scanning the stem diameter and length at harvesters (both figures

*Log yards* of forest enterprises and wood processors are equipped with cross-cutting-sorting carriages (all round cars) or lines. The equipment serves for the preparation of supplies of logs to manufacturing plants or for the preparation of logs according to requirements of subsequent production (With respect to the increasing proportion of harvester logging

revised (even several times per shift).

negligible.

according to Ponsse).

/generally/ the importance and number of log conversion depots declines). Scanning equipment for the log diameter and length is always part of the equipment. At scanning the log diameter, the number of taken values of the log diameter in one place of length, direction of scanning, accuracy and density of scanning in the course of length are essential.

*One-directional way of scanning - 1D* takes the value of the log diameter in one, usually vertical direction. As for possible technical designs, measuring frames are used nearly exclusively. The principle of scanning indicates a scheme on Fig. 3.

One-directional scanning is not able to record the log flattening and only very roughly the log curvature.

Using 1D scanning devices for the purpose of electronic reception is, therefore, unsuitable and results are affected by relatively considerable errors.

*Bi-directional measuring (2D)* is carried out by two systems perpendicular at each other and placed in one frame. It can be installed in such a way one scanning to proceed in vertical direction and the second scanning in horizontal direction or both measurements perpendicular at each other to proceed at an angle of 45° with respect to a horizontal level.

Fig. 3. The principle of scanning the log diameter by a one-directional scanning frame.

The substantial advantage of *2D* scanning consists in the better record of the measured log form and thus a possibility to calculate objective values of the log diameter in the place of measurement. The evaluation of stem curvature (sweep) is markedly more accurate. To calculate the log volume both methods of placing the sensing elements are equivalent. However, vertically and horizontally oriented sensors record flattening the measured logs better – a flattened log shows a tendency "to lie down flat" on the conveyer, i.e. vertically measured diameter shows a smaller value than a diameter measured horizontally. At systems oriented at an angle of 45° this difference disappears and both data approach the average value of log diameter in a given place.

scanning cameras

Laser sources of light (creating the "light cross section")

Fig. 5. The lay-out of a configuration for scanning the surface curve (3D measurement)

Fig. 6. Principles of measuring the log length by means of a pulse generator and a photocell.

(according to Microtec).

a log on the conveyer

(a) vertical and horizontal position of scanning systems (b) placing the scanning systems at an angle of 45°

Fig. 4. 2D measurements by a scanning frame. Both systems are placed in one frame. The conveyer can come through the place of measurement (a) or it is interrupted (b).

From the aspect of taking log diameter it is better when the conveyer is interrupted in the place of measurement. Thus, measurements are not affected by "erroneous" data caused by the transport track and passing drive dogs, which have to be subsequently filtrated by special program equipment. However, from the aspect of scanning the log length and mainly evaluation of the stem curvature (generally form) change of the log position on the conveyer is "more dangerous". It will be recorded by the sensing device as a change in the diameter position; however, the sensor is not able to differentiate if it was caused by the log curvature or by the change of its position on conveyers. Unfortunately, the conveyer interruption supports the change of the log position.

*Scanning the peripheral curve* (3D measurements) makes possible to scan the whole form of the log cross-section in the measured place. There are more principles of scanning and at some equipment, they are also combined. Usually, an intensive narrow light line is projected on the log in the place of measurement perpendicular to its axis. The light "cross section" is subsequently taken by cameras. Based on their signal, the form and position of the cross section is constructed and the area centre is evaluated. Subsequently, distances are evaluated of opposite points (i.e. log diameter) usually at least in an interval of 5° (36 values of the log diameter). Changes of the cross section position in the course of scanning of the whole log length make possible to evaluate the stem curvature and form anomalies.

The accuracy of diameter scanning ranges usually within the limits ±1 to ±2 mm. Values of diameter are evaluated usually at 10 cm intervals of the measured log length.

*Systems for scanning log lengths* were reduced in the course of development, namely to a laser system using the phase shift between the sent and received ray of laser and a system with a pulse generator and a photocell. The second system is used in the majority of cases in Europe. In the Czech Republic, the system is used exclusively.

The drive of a pulse generator is derived from the conveyer drive. The conveyer wheel diameter, gear ratio, and the number of pulses generated by the generator per one

Fig. 4. 2D measurements by a scanning frame. Both systems are placed in one frame. The

From the aspect of taking log diameter it is better when the conveyer is interrupted in the place of measurement. Thus, measurements are not affected by "erroneous" data caused by the transport track and passing drive dogs, which have to be subsequently filtrated by special program equipment. However, from the aspect of scanning the log length and mainly evaluation of the stem curvature (generally form) change of the log position on the conveyer is "more dangerous". It will be recorded by the sensing device as a change in the diameter position; however, the sensor is not able to differentiate if it was caused by the log curvature or by the change of its position on conveyers. Unfortunately, the conveyer

*Scanning the peripheral curve* (3D measurements) makes possible to scan the whole form of the log cross-section in the measured place. There are more principles of scanning and at some equipment, they are also combined. Usually, an intensive narrow light line is projected on the log in the place of measurement perpendicular to its axis. The light "cross section" is subsequently taken by cameras. Based on their signal, the form and position of the cross section is constructed and the area centre is evaluated. Subsequently, distances are evaluated of opposite points (i.e. log diameter) usually at least in an interval of 5° (36 values of the log diameter). Changes of the cross section position in the course of scanning of the

whole log length make possible to evaluate the stem curvature and form anomalies.

diameter are evaluated usually at 10 cm intervals of the measured log length.

Europe. In the Czech Republic, the system is used exclusively.

The accuracy of diameter scanning ranges usually within the limits ±1 to ±2 mm. Values of

*Systems for scanning log lengths* were reduced in the course of development, namely to a laser system using the phase shift between the sent and received ray of laser and a system with a pulse generator and a photocell. The second system is used in the majority of cases in

The drive of a pulse generator is derived from the conveyer drive. The conveyer wheel diameter, gear ratio, and the number of pulses generated by the generator per one

conveyer can come through the place of measurement (a) or it is interrupted (b).

(b) placing the scanning systems at an angle of 45°

(a) vertical and horizontal position of scanning

interruption supports the change of the log position.

systems

Fig. 5. The lay-out of a configuration for scanning the surface curve (3D measurement) (according to Microtec).

Fig. 6. Principles of measuring the log length by means of a pulse generator and a photocell.

mainly on the stem part, which was used for the log production. The method undervalues the volume of butt logs while top logs are overvalued. F.X. Huber was aware of this fact and, thus, for more accurate measurements, he recommended a section method. This method divides a stem to 1 or 2 m long sections and the volume of each of the sections is calculated separately using the way described above. The volume of a log is then the sum of volumes of particular sections. At the time of its origin, the method was used only for research operations due to its excessive time consumption. Due to similar causes even other

Procedures used at present for wood measurement and determination of its volume (from

Recommended rules for the measurement and classification/grading of wood in the

ÖNorm L 1021 Vermessung von Rundholz, Austria, 2006 (Österreichisches

 Rahmenvereinbarung für die Werksvermessung von Stammholz, 2005 (Deutscher Forstwirtschaftsrat e.V.& Verband der Deutschen Säge- und Holzindustrie e.V., 2005) Besides, there is a European standard EN 1309-2 Roundwood and sawn timber – Methods of measuring dimensions - Part 2: Roundwood – Requirements for measurements and rules for the volume calculation, 2006. Although it concerns a relatively new European standard, its use has not been found out in the CR. Its use (anywhere) limits not quite unambiguously determined methods of the determination of a mid diameter. A normative supplement B evokes also certain confusion. The normalized procedure of measurement is presented here as "rules for the measurement and calculation of the log volume valid if there are no state,

For users in Czech countries, it is suitable to include (from practical aspects) the CSN 48 0050 Standard "Raw timber. Basic and common provisions" into the survey of rules (ČSN 48 0050, 1992). This standard was used in the Czech Republic until the publication of "Recommended rules 2002". At present, it is not legally binding being virtually not used for timber reception. The majority of users are accustomed to results of measurements carried out according to the standard. The users compare often values obtained according to other rules with its results. Moreover, results of measurements carried out according to this

The analysis of methods of measurements includes all regulations and rules mentioned above talking into account also variants, which are determined or admitted by these

 Recommended rules for the measurement and grading of timber in the Czech Republic 2008 determine separate procedures for manual and electronic measurements, which

 ÖNorm L 1021 Vermessung von Rundholz makes possible calculations from mid diameter values given in mm or converted to cm in such a way that units in mm are not

 Rahmenvereinbarung für die Werksvermessung von Stammholz gives mid diameter and subsequent calculations of the log volume differently in the extent of log diameters

taken into account. The use of diameter values in cm is preferred.

procedures requiring more measurements were not used later in practice.

the aspect of their user in Czech Republic) are as follows:

Czech Republic, 2008 (Kolektiv, 2008)

standard were in very good agreement with reality.

regulations. It refers to following variants:

are not quite identical.

up to 20 cm and from 20 cm.

Normungsinstitut, 2006)

regional or district rules".

revolution gives the number of pulses per the conveyer line unit. A log moving on a conveyer cuts across the photocell ray and during its shading the photocell sends a signal. The number of pulses sent by the generator during the photocell shading gives the log length. Accuracy reached by this method of measurement ranges from ±1 to ±2 cm. Advantages of this method consist in its simplicity, reliability and non-sensitivity to the conveyer speed and its changes during measurement. Disadvantages consist in the photocell sensitivity to defects on the log end (chamfer cut, torn up fibres). Thanks to this fact, the system has a tendency to give excess values at logs with these defects. Erroneous measurements are also caused by the log shift on a conveyer.

Data on dimensions and shape of logs are also provided by scanners working on the principle of absorption of microwave radiation. Systems equipped with these scanners are primarily determined for scanning quality. Many defects (rot, knots, and growth anomalies) are often not visible from the stem surface being not noted at the visual checking the quality. Evaluation of scanned data at this method of scanning is however, substantially more complicated with respect to mutual relationships of more values (dimensions, density, moisture etc.). Thus, they are not used only for scanning dimensions due to their demands and costs.
