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This is an Accepted Manuscript of an article published by Taylor & Francis Group in Geodesy and

Cartography on 1/04/2015, available online: http://www.tandfonline.com/10.3846/20296991.2015.1011863

COMPASS MEASUREMENT – STILL A SUITABLE SURVEYING METHOD IN

SPECIFIC CONDITIONS

Julián Tomaštik1, Daniel Tunák2

Department of forest management and geodesy, Technical University, Zvolen, Slovakia

T. G. Masaryka 24, 96053 Zvolen, Slovakia

tomastik@tuzvo.sk1, tunak@tuzvo.sk2

Abstract. The compass measurement is one of the customary surveying methods that is used almost from the

beginning of systematic geodesy and cartography. After the periods of the decreased use of this method, it was

partially renewed by the ascension of the Field-Map technology that connects the compass measurement with the

software tools for the environment mapping. It is currently mostly used for the forestry under-canopy mapping and

other special tasks, where the current progressive technologies, especially photogrammetry and GNSS, can be used

only with complication. The Field-Map set can include either the laser rangefinder Impulse LR 200 with MapStar

Compass Module II compass, or TruPulse laser rangefinder that allows also the azimuth measurement. The research

was aimed on the accuracy of mentioned devices. The measured lengths and azimuth were evaluated primarily. The

evaluation of the field condition results showed the mean length error 0.07-0.09 m for Impulse rangefinder, while

0.25-0.29 m for TruPulse rangefinder. The mean azimuth error was around 0.5 degree for MapStar compass and

above 3 degrees for TruPulse. After this basic evaluation the data were used for the computation of four compass

traverses using various measurement and computation methods. The results showed, that the compass measurement,

especially using the Impulse+MapStar set, can be still a suitable method for lower accuracy surveying, although

effective only in specific conditions.

Keywords: compass measurement, Field-Map, accuracy, forestry mapping, laser rangefinder, electronic compass

Introduction

The use of compass measurement as a surveying method

gradually decreased in the past. It was caused mainly by

the increased number of the objects that interfere with the

Earth’s natural magnetism in urbanized areas and by the

rise of new technologies in the last periods, especially

photogrammetry and GNSS. The ascension of the Field-

Map technology caused a renaissance of compass

measurement as a distinctive method used in forestry

under-canopy mapping and some other specific tasks. It is

currently increasingly used in non-geodetic forestry tasks,

such as national forest inventory (O'Donovan 2007;

Buksha et al. 2010), forests research (Cienciala et al.

2013), and the like. The technology of terrestrial and

airborne laser scanning could complement or even

substitute the use of the compass measurement for this

type of tasks in the future, but there is still a need to

resolve a number of technological and methodological

problems (see e.g. Smreček, Danihelová 2013;

Hackenberg et al., 2014). Another option could be the

indoor positioning systems (e.g. Mautz 2009, Curran et al.

2011), but the main disadvantages – low accuracy,

sophisticated infrastructures, limited coverage area and

inadequate acquisition costs – remain unsolved despite the

partial progress.

The main focus when determining the compass

measurement accuracy should be on primary measured

parameters, i.e. lengths and azimuths. They represent the

polar coordinates of each point and their errors cause the

positional shift. Višňovský, Čihal (1985) derived the

equation for the positional shift of the last point of the

compass traverse:

, (1)

where d is the total length of the compass traverse and s is

the average side length. The 0.004 coefficient takes the

standard errors of the azimuths and lengths into account

when using the devices available at that time. For the

length measurement it was the error ±25 cm at 100 m

using the stadia rangefinder, causing the longitudinal

displacement. For azimuth measurement the error was 10',

which caused lateral displacement 29 cm at 100 m.

The primary objective of this work was to assess the

accuracy and usefulness of the compass measurement

using the electronic devices, which are part of the Field-

Map sets. Sub-tasks were to determine the accuracy of the

measured azimuths and lengths, and then determine the

overall positional accuracy based on the values of the

positional shift of the last compass traverse break-point

and mean coordinate errors. Thereafter assess the usability

of examined measurement for various tasks by comparing

these values with the prescribed criteria.

Materials and Methods

The Field-Map set is modular and its components can be

changed according to user needs. In principle it consists of

surveying equipment to measure angle and length, support

(tripod) and field computer with Field-Map software.

Optionally it may include the GNSS receiver. The devices

for the compass measurements are: (i) TruPulse 360B

laser rangefinder that also allows the azimuth

measurement or (ii) the set of Impulse LR200 laser

rangefinder and MapStar Compass Module II compass.

These tools combined with the simple support (monopod)

were used in the present research. Field computer was not

used because the format of recorded data would not allow

their analysis.

When examining the used electronic devices it is clear

already by using the manufacturer provided data that some

changes in terms of accuracy have occurred. For the

Impulse LR200 rangefinder the manufacturer specifies the

length error 3 cm at 50 m and 5 cm at 150 m, which varies

according to the target quality. It is, therefore, a positive

change over the use of stadia rangefinder. For the MapStar

Compass Module II compass the manufacturer declares

the ±0.3 degree error that is about 20'. This value is two

times worse than the stated error of older devices and at

100 m it causes the lateral displacement of 0.52 m. After

substituting these values declared by the manufacturer, the

equation for calculating the positional shift changes to:

, (2)

For the TruPulse 360B device the declared error values

are even higher. For the length measurement manufacturer

declares the value ±30 cm for targets designated by the

manufacturer as "typical". These are probably targets with

good reflectivity, but it is not stated to which measured

length the error applies. For "very far" targets with less

reflectivity the manufacturer declares the value ±1 m. The

value ±30 cm at 100 m was used for the purpose of

adjusting the positional shift equation. For the azimuths

measurement, the manufacturer declares the mean error

±1 degree. This is a value where it is very difficult to talk

about the use in geodesy, as at 100 meters of measured

length it causes lateral displacement 1.75 m. However,

such a value could be suitable for other applications, in

particular in combination with shorter lengths of measured

sides. Using these values to calculate the mean error

coefficient in the positional shift equation it can be

modified as follows: , (3)

According to the above equations, it is clear that the

accuracy of compass measurement using new electronic

devices is lower to the to conventional compass

measurement devices already according to the values

declared by the manufacturer. This is mainly caused by

the lower azimuth measurement accuracy.

The above equations represent the theoretically achievable

accuracy in the use of these types of devices. It is

questionable in what conditions were the manufacturer

declared values achieved and therefore it is very important

to verify them through the practical measurement. Two

point fields were designed to meet this goal in the first

phase of experiment, separately for lengths measurement

and separately for azimuths measurement. The point field

on the straight part of the road in Technical University in

Zvolen areal was used for the lengths measurement. It

consisted of device occupation point and 11 points, which

were at distances 5, 10 meters and in 10 meter intervals up

to 100 meters. Maximum length was chosen because of

the small magnification of the optics used in specified

devices and because the use of monopod, where the lack

of precise stabilization complicates the measurement of

longer distances. Also the Technical guide of the forest

management (1984) declares the maximum side length of

the compass traverse to 70 m, but this was required when

using conventional devices for compass measurement.

Points were set out using the combination of measuring

tape and TOPCON GPT3002 total station. Despite the

multiple measurements, the lengths cannot be stated as

absolutely precise and it is needed to take the 1 – 2 cm

error into the account, especially for those more remote

points. Points have been set out in two lines in order to

allow the measurement of two alternative lengths. This

procedure was chosen in order to avoid any potential

memory effect of the rangefinder when measuring the

same length. The measurement device and also reflective

prisms were built on tripod.

The measurement of exact azimuth values is quite

difficult, because these vary with place and time. All

systematic errors in their measurements, however, can be

removed by taking the value of the orientation deviation

into account, which essentially represents the difference

between the azimuth and the grid bearing determined for

fixed geodetic points. The determination of the orientation

deviation, which incorporates magnetic declination and

meridian convergence, should be the part of every

evaluation of the compass measurement (Žihlavník 2009).

The simple point field, consisting of device occupation

point and 4 points, was also designed for the purpose of

determining the azimuth measurement accuracy. These

points were situated approximately in the 4 cardinal

directions. First point was stabilized approximately in the

North direction and the other 3 were set out with 100 g

offset using the total station. Points were stabilized at a

distance of about 10 m from the device occupation point

to avoid the ambiguity when targeting as much as

possible. The device has been built on tripod to limit the

impact of imperfect centration, leveling and other errors

which occur when measuring with the use of simple

support (monopod), respectively free-hand.

The basis of compass measurement is a compass traverse,

which presents the polygonal line, where the mutually

independent magnetic azimuths of the traverse sides are

measured.

There are basically two main methods of compass traverse

measurement:

- measurement on each traverse break-point

- measurement on even traverse break-points,

measurement "with skipping".

When measuring using the first method on every break-

point, both direct azimuth to the next point and inverted

azimuth to the previous point are determined. The length

of the side is also measured two times. Due to the higher

labor intensity and the need to comply with the difference

criteria between direct and inverse azimuth is this method

rarely applied in practice. Using the faster and more

economical method of measurement on even break-point

the compass measurement device is built only on each

other break-point. The inverse azimuth of the previous

side and direct azimuth of the next side is measured along

with the side length. The next point is skipped and the

device is built only at the other break-point. Reverse

azimuths are converted to direct azimuths by adding or

subtracting the value of 2R. The disadvantage of this

measurement method is that it is not possible to verify the

correctness of the azimuth and length measurement. The

principle of both methods is shown in Fig. 1.

Fig. 1. Two methods of compass traverse measurement

The point field that was used in the second experiment

phase was founded for the purpose of verifying the

accuracy of various geodetic surveying methods in the

forest environment. It consists of 73 points, whereby four

compass traverses with length of 772.0; 587.88; 426.33

and 166.66 m were used; the number of break-points is

26, 17, 20 and 8. The point field was founded near the

village Sielnica (SK), with the detailed points mainly on

the borders of forest stands belonging to the University

forest enterprise TU Zvolen. Individual points were

stabilized using wooden or iron stakes eventually using

colored cross and surveying nail. The coordinates of

points were determined using the total station TOPCON

GPT3002 and combination of various measurement

methods (polygonal traverse, method of polar

coordinates). Obtained data were used as the reference

etalon for the compass measurement, because according to

the reported standard measurement errors the total station

is significantly more precise than the devices used for the

compass measurement. Also, the experimental

measurements confirmed the possibility of achieving

centimeter accuracy using the indicated total station (e.g.

Žihlavník 2012; Žihlavník, Tunák 2010). The point field

was designed to suit the compass measurement, because in

opposite to for example GNSS there is a need for

intervisibility between the adjacent geodetic points.

Consequently, one of the main disadvantages of the

methods, which require visibility between adjacent points,

is the large number of "surplus" points needed to set-out a

straight line in the forest. The side lengths were in range

from 12.01 m to 84.79 m. Overall, the side length of 60 m

was exceeded only four times. The location of point field

and the course of individual compass traverses is shown in

Fig. 2

Fig. 2. The point field location and the course of individual

compass traverses

The measurement of individual compass traverses was

conducted using the method of measurement on even

traverse break-points, "with skipping". Using this

method, the side lengths and the azimuths were measured

only once, in contrast to the measurement on each break-

point. The tripod was not used unlike the previous phase

of the experiment. The set Impulse + MapStar was built

on a monopod and the measurement was realized with

enabled and disabled “Level Aid” function, which is used

to level the apparatus on the stand. The measurement with

TruPulse 360B took place using a monopod as well as

free-hand without support. The reflective prism was

placed on a pole with leveling according to the bubble

level. All readings were recorded by hand in notebooks,

because the Field-Map software currently does not have

an option to record readings for the purposes of geodetic

measurements. The orientation deviation 8,59o was

determined for the transformation to the used S-JTSK

coordinate system. All azimuths were modified using this

value before the computation of orthogonal coordinates.

Three methods were used to determine the orthogonal

coordinates of compass traverses break-points:

- the calculation of the point coordinates in

succession, without adjustment

- length adjustment of the compass traverse

- the method of polar coordinates, using the etalon

coordinates of device occupation point

The evaluation was conducted separately for each

compass traverse and after that the summary result were

calculated for the entire set of surveyed points. The mean

coordinate error mxy as well as mean errors of measured

lengths and azimuths were used as basic comparative

values for individual compass traverses, as well as the

methods of measurement and evaluation. Those were

calculated as the difference between the etalon values and

the values acquired using the Field-Map set.

Results

Each length of the first phase experimental point field was

measured 30 times. Subsequently, the average value, the

error of average value and the standard deviation were

calculated. Obtained values are shown in Tab. 1.

Table 1. Average values, average value errors and standard

deviation of obtained lengths according to used device [m]

Impulse LR200

Trupulse 360B

length

σ

σ

5

4.98

-0.02

0.06

5.08

0.08

0.2

10

9.95

-0.05

0.03

9.99

-0.01

0.16

20

19.94

-0.06

0.01

19.88

-0.12

0.11

30

29.97

-0.03

0.01

29.89

-0.11

0.07

40

39.98

-0.02

0.01

39.92

-0.08

0.05

50

49.97

-0.03

0.01

49.98

-0.02

0.06

60

60.01

0.01

0.01

60

0.00

0.05

70

70

0

0.01

70.03

0.03

0.05

80

80.01

0.01

0.01

80.03

0.03

0.05

90

90

0

0.01

90.02

0.02

0.05

100

99.98

-0.02

0.01

100.05

0.05

0.05

From the data shown, especially after taking the etalon

point field error into account, it is obvious that used

rangefinders achieved rather good results. It is important

to note that the Impulse LR 200 length resolution is 0.01

m, while for TruPulse 360B it is 0.1 m. The values of

lengths error were tested for the presence of the bias using

the Student t-test. The critical value t0,05(29) = 2,045 was

repeatedly exceeded during the individual lengths tests

using the values obtained by Impulse LR200, as well as

TruPulse 360B. It could be generalized that lengths up to

60 m are slightly underrated, while lengths over 70 m are

slightly overrated using the TruPulse 360B. This is also

evident from Table 1. In most cases, however, the values

are below 0.1 m, what is the TruPulse 360B length

resolution. The test criterion was also similarly exceeded

using the Impulse LR200. However, the average length

errors were relatively small. At such as low values it is

necessary to consider the errors of etalon lengths. Overall,

it can be concluded that the accuracy of length

measurement did not exceed the values stated by the

manufacturer. However, it must be remembered that these

are the values obtained using a tripod and reflective prism.

Both devices have the ability to measure lengths without

the reflective prism, but it is often very problematic,

especially in forest area.

The azimuth measurement in first phase of experiment

was conducted 30 times in all 4 directions. Computed

average values of azimuths, standard deviations and

reduced differences are noted in Table 2. The reduced

differences were calculated using the average value of

first azimuth and consequently the basic direction value.

Table 2. Average values, standard deviations and reduced

differences of obtained azimuths according to used device

Mapstar Compass

Module II

Trupulse 360B

average

value

standard

deviation

reduced

difference

average

value

standard

deviation

reduced

difference

Direction

0o

2,11o

0,32o

0o

2,47o

0,10o

0o

90o

92,29o

0,21o

0,18o

94,35o

0,14o

1,88o

180o

182,19o

0,42o

0,08o

184,45o

0,18o

1,98o

270o

271,97o

0,15o

-0,14o

273,10o

0,12o

0,63o

At a superficial analysis of these values, it would appear

that the MapStar Compass Module II is less precise, since

the dispersion of individual measurements around the

average value is higher. However, when comparing the

values of reduced azimuths, it is obvious that using the

MapStar compass the highest difference is 0.18 degree, in

opposite to 1.98 degree using TruPulse. The result is that

the Mapstar compass measurements were more or less

consistent in whole circle range, but TruPulse acquired

azimuths which were 2 degrees higher in 90o and 180o

directions in comparison with the other two directions.

Nor the recommended calibration did help. It shifted the

angles systematically, but the differences in each direction

remained unchanged. Also, the measurements at another

site confirmed this fact. As there was no opportunity to

compare this measurement with the other measurement

using device of the same type, it would be wrong to

generalize these results. However, if confirmed, this

would be a serious complication, because an error of this

nature is hardly removable by user. The result of the first

phase of the experiment confirmed that the precisions

indicated by the manufacturer are real, but the

measurement of shorter lengths for both types of devices

and inconsistent azimuth measurement using the TruPulse

360B is problematic.

Four compass traverses with different total length and

average length of the side were used in the second phase

of the experiment. Obtained results present the average

values of 4 measurements, conducted in 2010-2014. As

mentioned, when determining the accuracy of surveying

equipment it is necessary to determine the accuracy of the

primary obtained parameters first, which were the lengths

and angles in this case. The length and azimuth errors

were calculated for each side of used compass traverses.

The mean squared error for each variant of measurement

was computed using these errors. The results are listed in

Table 3.

Table 3. Mean squared errors of azimuths and lengths according

to measurement variant

IMPULSE+

MAPSTAR

TRUPULSE 360B

without

leveling

with

leveling

monopod

without

support

azimuth (o)

0,51

0,48

3,12

3,24

length (m)

0,09

0,07

0,25

0,29

Subsequently, the measured lengths and azimuth were

used in the calculation of orthogonal coordinates of all

break-points in the S-JTSK coordinate system. Three

methods of calculation were used. The first was the

calculation of orthogonal coordinates from polar

coordinates using the occupation point coordinates from

comparative etalon, which eliminates the transfer of

errors, because the coordinates of each point are

calculated separately based on the coordinates of the

occupation point and measured azimuth and length.

Furthermore, two methods of traverse evaluation were

used - without adjustment and with length adjustment,

where the break-point coordinates are calculated one after

another, what leads to the transfer of errors. After the

calculation of coordinates, these were compared to the

etalon coordinates. Coordinate errors for each break-point

and subsequently the mean coordinate errors were

computed according to different methods of measurement

and calculation, as is shown in Fig. 3.

Fig. 3. Mean coordinate error values according to measurement

and computation method

The above figure confirms the significant difference

between the accuracy of used devices. Differences for

each device with and without leveling (resp. using

monopod and without using it) are minimal. It should be

noted that the point field was located in a slightly warped

terrain. It can be assumed that the measurement in more

hilly terrain would be more affected by the correct

leveling.

The presented values of mean coordinate errors mxy

depend on the lengths of sides and the general compass

traverse configuration and therefore cannot be regarded as

universally valid. It is needed to judge the measurement

accuracy of used devices according to the positional shift

of the last point, as was marked above in equations (1)-

(3). Višňovský, Čihal (1985) stated that the maximum

deviation qmax=2,5q , (4)

will in case of connected or closed compass traverse

represent the allowable misclosure of numerically solved

compass traverse. Therefore, misclosures of every

compass traverse were determined according to the

measurement method. At the same time, the expected

values of the position shift q were calculated according to

the equations (2) and (3) for each compass traverse and

used device. These values are shown in Tab. 4.

Table 4. Basic characteristics of experimental compass

traverses, predicted positional shifts and obtained positional

misclosures according to used equipment and measurement

variant [m]

traverse

1

traverse

2

traverse

3

traverse

4

total

traverse

length

772.00

587.88

426.33

166.66

average side

length

32.17

36.74

22.44

20.83

qimpulse

0,95

0.88

0.59

0.35

misclosure

Impulse

without

leveling

0.65

1.16

0.82

0.77

Impulse

with

leveling

0.73

0.99

0.98

0.69

qtrupulse

2,84

2.65

1.76

1.06

misclosure

Trupulse

with

monopod

2.98

4.38

0.52

1.52

Trupulse

without

support

5.46

5.4

0.89

1.92

The results showed that the maximum deviation, equal to

2.5q was not exceeded in either case. Using the Impulse+

MapStar set misclosure was 0.7 to 2.2 times higher than

the predicted positional shift, using TruPulse 360B 0.3 to

2.0 times higher. The results also showed that equations

(2) and (3) are suitable for the prediction of compass

measurement accuracy with the use of examined

measurement devices. Of course, the reliability of this

conclusion should be confirmed by additional

measurements of compass traverses with different overall

lengths and average side lengths.

Discussion

The obtained values provide information on practically

achievable frameworks of errors that may be expected

with 68% probability when using examined devices. The

resulting mean error may still contain the random and

systematic part. Random component decreases with

increasing number of measurements, but the systematic

component (the so-called bias) remains constant.

Therefore, when using the surveying equipment, it is

necessary to determine the presence of systematic errors,

and if present eliminate it. The methodology of the study

was adapted to this requirement.

Just a few authors devote themselves to the evaluation of

compass measurement at the present. For example

Potočnik (2010) compares the compass measurement with

Suntoo to the measurement with total station and two

different GNSS receivers. He assesses the compass

measurement as quick and easy, but with low accuracy.

Šebeň et al. (2006) reported the maximum length error up

to 10 cm with the use of Field-Map set including Impulse

LR200 rangefinder. Azimuth measurement accuracy was

not engaged. They evaluate the consequences of errors of

measured lengths in forest inventory, where inaccurately

measured radius of circular inventory plots (even with 1

cm error) can significantly distort the results derived from

the inventory plot data. Ruan (1995) deals with the

transfer from graphic to analytic evaluation of compass

traverse, but works with an ordinary compass. The paper

published by Brach et al. (2013) contains the methodology

and uses the equipment that is closest to the one used in

the presented paper. Authors achieved almost the same

results in terms of mean errors of length and azimuth and

also the alike mean coordinate error.

In general, the examined devices achieved lower accuracy

in comparison to older device for compass measurement.

It is clear already from the accuracy values provided by

the manufacturer. When measuring lengths using the both

devices, paradoxically, the highest deviations and

variances were achieved at lower lengths. When using the

Impulse LR200 rangefinder, the reason could be in the

mismatch of telescope axis and measurement laser. For

lengths up to about 25 meters there is a need to place the

aiming crosshair more or less above the reflective prism,

thereby increasing the ambiguity of the aims and

apparently affecting the elevation angle, which is used in

the calculation of the horizontal distance. When using the

TruPulse 360B, this problem is not so significant, but

nevertheless errors are larger at lower lengths. This

finding is important, because the standard tasks where

Field-Map sets are used, often require the measurement of

lower lengths. Also the principle of the compass

measurement described in equations (1)-(3) says, that in

contrast to polygonal traverse, compass traverse is more

precise when the sides are shorter.

The evaluation of values achieved through the practical

measurement of compass traverses showed, that the values

for Impulse+Mapstar set are twice as high as the value

specified by the manufacturer. However, it should be

considered that the value of the resulting measurement

error includes not only the error of the device itself, but

also a variety of other errors, e.g. imperfect leveling error,

imprecise targeting, non-centric emplacement of the

device and the target, and so on. Similarly, the

comparative etalon values cannot be stated as absolutely

accurate, even when obtained using the devices with

rather high accuracy. Comparing to the conventional

devices for compass measurement, it can be stated that the

mentioned Impulse+Mapstar set achieves better results for

the lengths measurement, but only about 3 times worse

results for azimuth measurement. Using TruPulse 360B,

the length measurement error matches the value stated by

the manufacturer and is comparable to the values

achievable using the stadia rangefinders. In contrast, the

azimuth error is very high. The value above 3 degrees

would virtually rule the possibility of using the device for

surveying tasks out and also the use for other purposes

would be very questionable. Apparently the combination

of azimuths of the compass traverses sides in conjunction

with the inconsistent measurement caused such a high

error. Besides that, it is not a systematic error, since the

critical value for testing the bias was not exceeded. The

existence and the possible solution of such a high error

must be confirmed through the more future measurements.

Comparing the evaluation methods, the polar method with

the use of etalon coordinates of occupation points was

confirmed as the most accurate. In practice, this method

could be used in a combination of the mentioned devices

with other surveying methods, where the position of the

occupation point would be determined by more accurate

method (e.g. GNSS) and the surrounding topography

would be measured using noted devices. It is important

that with this method, the measured points (resp. azimuths

and lengths) do not influence each other. When using this

method and the Impulse + MapStar set, the criterion for

the 4th accuracy class according to the Slovak technical

standard STN 01 3410 was fulfilled, which is required for

the cadastral mapping outside the urbanized areas (forests,

agricultural areas). The other two methods represent the

traverse solution; ergo the coordinates of the points are

calculated sequentially and are mutually connected. This

causes the significant increase of the mean coordinate

error. The calculation without adjustment is a standard

procedure of the Field-Map use, where the first occupation

point is a known geodetic point, but the traverse is not

finished on another known point. Therefore the

adjustment is not possible. The calculation with

adjustment is possible when the compass traverse is

inserted between two known geodetic points. In that case,

the length adjustment is possible. The considerable

information for the practice is, that the final accuracy

within 1 meter could be achieved using the

Impulse+Mapstar set, which corresponds to the sum of the

traverse calculation without adjustment (establishing

occupation points) and polar method (measurement of

surrounding topography). The values obtained using

TruPulse 360B were significantly higher. Another

criterion, used in practice of Slovak forestry mapping is,

that the maximum misclosure of graphically evaluated

connected or closed compass traverse should not exceed

the 2% of the total traverse length. However, the accuracy

of the graphical evaluation is reflected in this criterion in

addition to the measurement precision. For the

experimental traverses this value means 15.4 m for

traverse 1, 11.8 m for traverse 2, 8.6 m for traverse 3 and

3.4 m for traverse 4. The obtained real misclosures are

lower than noted maximum misclosures in every case.

Based on the obtained results it can be stated that compass

measurement, even when using electronic devices, may be

still an applicable method for surveying tasks with lower

accuracy demands. These results showed that the source

of the highest errors is the azimuth measurement. These

cause the lateral displacement depending on the length of

the side to which was subsequently added the longitudinal

displacement caused by the error of the length

measurement. Thus it is confirmed, that it is preferable to

choose a larger number of shorter sides when using

compass measurement. The remaining advantage of

compass measurement over the use of theodolites,

tachymeters, respectively total station remains is the lower

demand on the existing point field, because no orientation

points are necessary for determining the basic direction. It

is especially convenient in rural areas where the point

field is sparse. Similarly advantageous is the possibility to

use a monopod, which facilitates and accelerates the

device stationing in the field. Despite the above result the

efficient use of compass measurement is currently more or

less limited only to under-canopy measurements in

forests, underground areas and other areas especially with

the obscure reception of GNSS signals. The reason is the

high efficiency of the photogrammetric evaluation of

elements that are identifiable on photogrammetric images

as well as the possibility of using global navigation

satellite systems. The accuracy of GNSS methods in areas

with good signal reception is much higher, while the time

consumption can be lower when compared to the compass

measurement. The results of the evaluation method using

the etalon coordinates of occupation points may show the

potential for increased accuracy in combination with other

methods, where the more accurate method will be used to

achieve the coordinates of occupation point (e.g. GNSS)

and the surrounding topography would be measured using

the method of polar coordinates for compass

measurement. The practical problem for using such a

combination, especially in forestry mapping, is, that the

linear objects, which are most widespread in forestry

mapping, cannot be measured from one occupation point,

while the correct determination of position using GNSS in

forest is problematic.

When using the national grids, as was the S-JTSK system

in actual study, it is very important to include the value of

the orientation deviation. It cannot be substituted by

magnetic declination; the meridian convergence must be

also taken into account. Therefore it is necessary to

determine the orientation deviation for every compass

measurement either by direct measurement (comparison

of grid bearings and azimuths on the known points), or by

calculating the magnetic declination and meridian

convergence for the particular area.

Conclusion

The current period is characterized by an increased

demand for spatial information in virtually all fields of the

human activity. These are often made available to the

wide public. The quality of the data, which is conditioned

by their origin, is often overlooked during the process of

creating and filling a variety of geographic information

systems. In the process of the introduction of new

technologies for obtaining these data it is therefore very

important to look not only on the efficiency of their use,

but also on the spatial accuracy of the data.

With regards to the achieved results the following

conclusions can be drawn:

- the mean coordinate error under 0.5 m can be achieved

by using the Impulse+MapStar set and compass

traverses with short sides and short total lengths. The

results when using the TruPulse device are many time

worse.

- the main source of error of examined devices is the

azimuth measurement.

- the fact, that compass traverses with shorter average

side lengths are more accurate, remains valid.

- it is necessary to keep clean from objects that affect

the Earth's natural magnetism.

- in terms of efficiency and relative small effect of

leveling choose as simple set as possible (preferably

with monopod).

- it is important to take the value of orientation deviation

into account when connecting the measurement into

the national grid.

The compass measurement is currently mostly used in

forestry research and forestry inventory. For this purpose,

it is sufficiently effective and fast. . The measurements in

forestry research are conducted mostly in local coordinate

system that is generally not necessary connected to the

geodetic points. In the field of research and inventory the

compass measurement successfully replaces customary

surveying methods, based on the measurement method in

the local orthogonal coordinate system using simple tools

such as stakes and steel tape. Compared to these methods,

the compass measurement with the use of laser

rangefinder and electronic compass is less laborious and

time-consuming. The important contribution to the

application of compass measurements as an appropriate

method for detecting the state of the environment is the

ability to use specialized software for automated

processing of measured data, which represents the

perspective for the preservation and further development

of tools for compass measurement. The main disadvantage

is the smaller effectiveness and accuracy in most areas,

where the GNSS or photogrammetry can be used. For that

reason the effective use of compass measurement is

currently limited to the forest under-canopy measurements

and some other specific measurements (for example

subterranean) where the actual most efficient methods

cannot be used without complications.

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Acknowledgement

This publication is the result of the implementation of the

project VEGA MŠ SR and SAV no.

1/0804/14:”Actualization of mapping, arrangement of

forest land ownership and determination of landscape

status by modern methods of geodesy and aerial survey”.