Garmin GPS manual

GPS Field guide © WHO 2002[...]

09/25/02 GPS_field_guide 8:19 A9/P9 2 CONTENTS CHAPTER 1: I NTRODUCT ION TO GPS 1.1 What is GPS ?…………………………………………………………...2 1.2 How does GPS work ?…………………………………………………..3 1.3 Source of GPS signal errors……………………………………………...7 CHAPTER 2: [...]

09/25/02 GPS_field_guide 8:19 A9/P9 3 CHAPTER 1: INTRODUCTION TO GPS 1.1 What is GPS? The Global Positioning System (GPS) is a syst e m allowi ng to precise ly identi fy loc ations on the earth 's surface. The GPS system has 3 parts (Figure 1): · The Spac e segment : a network of 24 satellites placed into orb it (Figure 2). The first GPS sate[...]

09/25/02 GPS_field_guide 8:19 A9/P9 4 1.2 How does GPS work? GPS satellites circle the Earth twice a day in a very precise orbit at an altitude of around 19 000 Kilo metr es ( Fig ure 2) . T his co nste llatio n al lows a ny u ser to acc ess be twee n fi ve and eight sate llites from any point on the Earth . Figure 2 : The GPS Satellite network Eac[...]

09/25/02 GPS_field_guide 8:19 A9/P9 5 The receiver: 1. Calculates the distance to the first satellite he is able to catch. Let's suppose that the receiver calculates a di stance of 17 '000 km between this first satellite and the receive r. This will mean that the receiv er is located somewhere on a sphere that is centred on this first sat[...]

09/25/02 GPS_field_guide 8:19 A9/P9 6 3. Repeats the operation mentioned under point 2 with a third satellite. In our ex ample the receiver finds out that it is 20,000 km from the third satellite which narrows its position down even further, to the two poi nts (Figure 5 point b) wher e the 20,000 km sphere cuts through the circle reported on Figure[...]

09/25/02 GPS_field_guide 8:19 A9/P9 7 1.3 Sources of GPS signal errors Even if today's GPS receivers a re ext remely accurate, c ertain atmosphe ric factors and other sources of error c an affect the accura cy of GPS recei vers. If most of the sources of e rror are unavoid able, i t is important for the user to be aware o f the ones that he ca[...]

09/25/02 GPS_field_guide 8:19 A9/P9 8 There m a y also be so urces o f si gnal mult ipath ( i.e on Fi gure 8) occur ring whe n the GPS signal is reflect ed off these o bj ects before r eaching th e rece iver. This incre ases the travel time of the sign al and c reat es erro rs of d ista nce es timatio n be twee n the satelli te and the receiver. ·[...]

09/25/02 GPS_field_guide 8:19 A9/P9 9 CHAPTER 2: WHY USING GPS IN THE CONTEXT OF THE WHO WHS ? The fir st reason for using GPS in the WHS context is the added value it gives to the survey by allowing the geographical dimension to be taken into account without requiring impor tant inve stment (many GPS receivers are inexpensive, GPS data is free, an[...]

09/25/02 GPS_field_guide 8:19 A9/P9 10 CHAPTER 3: THE GARMIN ETREX UNIT The Garm in eT rex G PS re ceive r h as be en chos en fo r t he WH O W HS b ecaus e i t i s eas y to use and inexpensive. Its utilisation in the c ontext of diffe rent survey s operated in the field has proven its suitability for this kind of work. This device is completely wat[...]

09/25/02 GPS_field_guide 8:19 A9/P9 11 Figure 10 - Back view of the G armin eTrex device Table 1 describes the elements report ed on the Figures 9 and 10 Inside the waterproo f case are located a set of electronic compone nts that allow the receiv er to perform different operations and to disp la y the final result on the L CD screen through a spec[...]

09/25/02 GPS_field_guide 8:19 A9/P9 12 1. Intern al GPS Antenna This antenna a llows the receiver to tr ack satellites sig nals. Thus, when using the GPS, the unit should be parallel to the ground and facing upwards. Apart from the cover of the hol ster nothing should be put on this part of the unit as this may stop satellite signal. 2. LCD Displa [...]

09/25/02 GPS_field_guide 8:19 A9/P9 13 3.2 Utilisati on of the eT rex unit This se ction presents th e major elements th at will be used in the contex t of the WHO W HS. It introduces you to the basic features of th e eTrex as well as some b asic definitions of terms in a more detailed way tha n presented on the Quic k Reference guide. 3.2.1 Instal[...]

09/25/02 GPS_field_guide 8:19 A9/P9 14 3.2.3 The Garmin eTrex Pages Th e eTr ex op erat ing s yst em i s c omp osed o f dif fer ent pa ges or ganise d i n a hi era rchic al wa y starti ng fro m 4 m ain pa ges (Fi gure 12 ). Th e 'NOR MAL S KYV IEW SATELLIT E' p age is one of them. To Switch from one of these main pa ge to the other you ha[...]

09/25/02 GPS_field_guide 8:19 A9/P9 15 This information concerns: - The Status of the device. Two t ype of messages can appear: a) "WAIT… LOCATING SATELLITES" indicat ing that the r eceiver is tracking satellite sig nals. b) "READY TO N AVIGATE" i ndicating that the rec eiver has found satellit e signals strong enough to know [...]

09/25/02 GPS_field_guide 8:19 A9/P9 16 You can access to these two pa ges by pressing the ENTER button from the 'NORMAL SKYVIEW SATELLITE' page in order to open the 'OPTIONS' w indow. From there you can use the UP and DOWN but tons to h ighli ght the pa ge you want to acces s and press the ENTER button. Once you have finished wo[...]

09/25/02 GPS_field_guide 8:19 A9/P9 17 The 'ADVANCED SKYVIEW SATELLITE' page Thi s page con tain s the sam e eleme nts as the ' NORM AL SKYV IEW S ATELLI TE ' page but presented in a different graphical way (Figure 16). This display gives more information about the location of the satellites in the sky (represented as a numbere [...]

09/25/02 GPS_field_guide 8:19 A9/P9 18 Figure 17 - The ' MENU' page There are two options of interest for the W HS on the 'MENU' page: the 'MARK' and 'SETUP' ones. The Figure 18 allows you to visualise how to access to the structure of these two options. Figure 18 - Scheme to access the 'MARK' and &[...]

09/25/02 GPS_field_guide 8:19 A9/P9 19 The 'MARK WAYPOINT' option page Once the GPS receiver has be en set-up and that the user has found an op en area for the reading, this pag e will allow the user to visualise his location (Figure 19). Th e other information or options re ported on this pag e will not be used in the context of the WHS.[...]

09/25/02 GPS_field_guide 8:19 A9/P9 20 The 'UNITS' se tup page This page (Figure 21) allows the user to set up the units of the differ ent parameters. I t is important to make sur e that this pag e contains the setting specific to the WHS as indicated in t he Figure 21 a) and in the Quick R eference Gui de. Figure 21 - The 'UNITS&apo[...]

09/25/02 GPS_field_guide 8:19 A9/P9 21 CHAPTER 4: TROUBLESHOOTING 4. 1 eTrex do es not turn on: 1. Check to see if the batter ies a re installe d correctly and if the battery te rminals are clean. 2. If the eTrex does not turn on after point 1: place a fresh set of AA batte ries in the unit (r efer to Quick Reference Guide point n° 3 ' In sta[...]

09/25/02 GPS_field_guide 8:19 A9/P9 22 - eTrex then asks: 'IS TODAY dd-mmm-yy?'. Two possibilities: a) The date indicated matches the curr ent date : · Press UP/ DOWN buttons · Highlight 'YES' and press the ENTER button, the eTRe x will conti nue tr acki ng satellite s and sw itch to the Satellite page. b) The date is incor re[...]

09/25/02 GPS_field_guide 8:19 A9/P9 23 4.6 eTrex does n ot disp lay the lo cal time in th e 'SE TUP' pa ge The eTrex operate s on universal time (or GMT, Gree nwich Mean Time ). It is not necessary to have your local time display e d. Do not worry about a wron g display ed time. 4.7. T h e geographic coordinat es I get are outside the ran[...]

09/25/02 GPS_field_guide 8:19 A9/P9 24 GLOSSARY Accuracy : How close to t he real valu e a measur ement is. Backlight: Se lectable on/off illumination that lig hts the display f or enhanced screen a t night and in low lig ht. Contrast: The di fference betw een the li ghtest and darkest a reas on a displa y screen. Coordinates : The unique descripti[...]

09/25/02 GPS_field_guide 8:19 A9/P9 25 Variance: In this context correspond to the errors in magnetic compass re adings caused b y variance in the earth 's magne tic field at different locations on the planet. Waypoint: Current location on the face of the Earth, in terms of the specific latitude/long itude coordinates. BIBLIOGRAPHY / LINKS Thi[...]