Use  of  various  survey  methods  in  forest  engineering  

Igor  Potočnik  

Accordo  n.  2012-­‐1-­‐IT2-­‐ERA10-­‐38840  

•  Geodetic measurements in all branches of construction has been present for a long time as a basis for planning and construction of various facilities

•  Only basic procedures of geodesy are in use in forest engineering which are unchanged for a long time

•  In the past two decades, surveying procedures improved in term of speed, accuracy and simplicity mostly due to use of computers and technical development in general

•  Recently, a very useful tool for field work in particular shows the GPS technology

•  Therefore we shall consider whether GPS technology can facilitate or improve surveying in forestry.

1 INTRODUCTION

• The aim of to paper is to study how different surveying methods are practically useful in the forest engineering

• The aim is also to determine whether existing surveying methods are still sufficient or need for better and more precise methods is already present

• We want to compare the accuracy between different geodetic techniques on various terrains and to examine the rationality of the use of different surveying methods.

2 RESEARCH OBJECTIVES

• Compass method is quick and easy, but inaccurate

• Handheld GPS, despite the simplicity and accessibility, is not suitable for detailed surveying due to imprecision

• Geodetic GPS is very accurate, but is not useful in areas with poor satellite signal and is very expensive

• Classic Wild RDS tachymeter is precise and relatively inexpensive, but requires skilled worker (surveyor) and takes much time than other methods

3 WORKING HYPOTHESES

• Research object is a section of a forest road on three different locations in three different environments (550 m of forest road, intersection 25 m)

• The •  first location is intended to represent an ideal situation, •  second most typical and •  third the most extreme situation

• At each location different surveying problems may appear so we can conclude which geodetic method is more and which is less suitable for specific terrain type

4 METHODS 4.1 Research object

• Location No. 1 is an open flat field, without any disturbing elements (hills, forests, villages, power lines or other major objects)

• The road is used as a tractor road to access to agriculture land.

Fig. 1: Location 1 and selected road section

4.1.1 Location 1

• Location No. 2 is a forest road providing access to the forest and access to the top of the hill as a tourist attraction

• many curves and steep longitudinal inclination

• The surrounding area is completely overgrown with mixed forest, tree canopies overgrow forest road.

Fig. 2: Location 2 and selected road section

4.1.2 Location 2

• Location No. 3 is a forest road located in the valley surrounded by high peaks (above 1.200 m above the sea level) and has the characteristics of the gorge

• Represents an extreme situation, with difficult access, although similar situation occurs often in mountainous regions

4.1.3 Location 3

Fig. 3: Location 3 and selected road section

Usefulness of four different methods of recording situations and the longitudinal profile on the selected objects:

•  compass method (Suunto), •  tachymeter Wild RDS, • GPS Garmin V, • GPS Thales Z-MAX.

Suunto Wild RDS Garmin V Thales

Fig. 4: Instruments used

4.2 Surveying methods

• There was no significant difference between surveying methods in term of measurement quality.

• Wild and Thales show comparable results • Garmin V was also fairly accurate, but with some deviations.

100

110

120

130

140

150

160

170

180

190

100 200 300 400 500 600 700

Coordinate Y

Coo

rdin

ate

X

Compass methodWild RDSGarmin VThales Z-MAX

Fig. 5: Bird's-eye view – location 1

5 RESULTS 5.1 Bird's-eye view

5.1.1 Location 1

• GPS based methods: surveying accuracy reduced due compact tree crowns.

• Wild and compass method have similar results

0

50

100

150

200

250

300

350

100 150 200 250 300 350 400 450 500

Coordinate Y

Coo

rdin

ate

X

Compass methodWild RDSGarmin VThales Z-MAX

5.1.2 Location 2

Fig. 6: Bird's-eye view – location 2

0,00

20,00

40,00

60,00

80,00

100,00

120,00

140,00

-500,00 -400,00 -300,00 -200,00 -100,00 0,00 100,00 200,00

Coordinate Y

Coo

rdin

ate

X

Compass methodWild RDSGarmin V

• GPS results the worst comparing to other surveying methods • Thales Z-MAX: unable to connect to the satellites • The whole bird's-eye view measured by Garmin V is distorted

especially in X axis • Surveying by Wild and compass was done easily

5.1.3 Location 3

Fig. 7: Bird's-eye view – location 3

344,00

346,00

348,00

350,00

352,00

0 50 100 150 200 250 300 350 400 450 500 550

Distance (m)

Hei

ght a

bove

sea

leve

l (m

)

Wild RDSCompass methodGarmin VThales Z-MAX

Fig. 8: Longitudinal profile – location No. 1

5.2 Longitudinal profile 5.2.1 Location 1

• Garmin V: scattered measurements (Z – height) • The most accurate measurements were obtained by Thales Z-MAX

and Wild RDS • Compass method showed worse results due to technical limitations

- manual clinometer cannot detect minimal changes of inclination (less than 1%).

5.2.2 Location 2

380,00

400,00

420,00

440,00

460,00

480,00

0 50 100 150 200 230 275 295 345 390 430 480 530

Distance (m)

Hei

ght a

bove

sea

leve

l (m

)

Compass methodWild RDSGarmin VThales Z-MAX

• Wild RDS and compass method: the most reliable picture. • Garmin V: good results at the beginning but precision is

insufficient under condensed growth - it varies up to 15 m. • Thales Z-MAX: incomplete measurements due to condensed tree

canopies and consequently bad satellite reception

Fig. 9: Longitudinal profile – location No. 2

•  GPS receivers not suitable for extreme terrain conditions with poor or no satellite signal (Garmin V - deviations up to 40 m are considered as completely not useful)

•  the compass method is less precise because of the measurement precision originated by the instrument's precision

515

525

535

545

555

565

0 40 75 115 165 210 260 310 360 410 460 510 550

Distance (m)

Hei

ght a

bove

sea

leve

l (m

)

Compass methodWild RDSGarmin V

Fig. 10: The longitudinal profile location No. 3

5.2.3 Location 3

Compass method: • quick and easy but is highly subject to errors, especially for

inexperienced

• Errors may occur easily and because of way of calculation the error is passed to the whole project

• Correction is possible only through the re-measurement

• Great advantage of the compass method is simplicity and low cost instrument beside the fact that it can be performed without extensive prior knowledge since it requires only basic orientation.

6. DISCUSSION AND CONCLUSION

Wild RDS

•  is a classic method in land surveying

• advantage of this method is time efficiency, high accuracy and flexibility

• disadvantage is necessity of theoretical and technical knowledge and high-cost instrument

•  the method provides a semi-solution that would benefit but for regular use in forestry is still too expensive and too precise for use in forest engineering.

Garmin V:

•  representative of the lower grade GPS receivers available and easy to use

• accuracy of the measurement yet not good enough for use in forest engineering

• measurements are subject to errors due to poor reception, especially Z coordinate

Thales Z-MAX

•  the most advanced of all the instruments used in present research

• precision comparable with conventional surveying methods, it is easy to use, and it is also easy for data processing

• disadvantages: high initial cost and limited use in forestry (very quickly lose the signal and precision) beside necessity of having knowledge of geodesy

Table 1: Factors influencing the choice of instrument (+: positive effect, -: negative effect, o: impact depends on user)

Device/Method Price Precision Applicability Complexity Total

Compass + - + + +

Wild RDS - + o - o

Garmin V + - - + -

Thales - + - - -