Tutorial De Gps Pdf
GPS observations and total station survey data integrated with local mapping and managed in GIS. Allowed us to reference the earth rotation to the direction of stable extragalactic radio sources with unbelievable accuracy, GPS has advanced geodetic capability by leaps and bounds in a variety of ways.
.GPS Field guide © WHO 2002.1.2 How does GPS work?3 1.3 Source of GPS signal errors.7 CHAPTER 2: WHY USING GPS IN THE CONTEXT OF THE WHO WHS? CHAPTER 3: PRESENTATION OF THE GARMIN ETREX GPS UNIT 3.1 Overview of the eTrex unit.10 3.2 Utilisation of the eTrex unit.13.
The Space segment: a network of 24 satellites placed into orbit (Figure 2). The first GPS satellite was launched in 1978 and a full constellation of 24 satellites was achieved in 1994. Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.8:19 A9/P9 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 Kilometres (Figure 2). This constellation allows any user to access between five and eight satellites from any point on the Earth.19'000 km. Or in other words, that the receiver is somewhere on the circle where these two spheres intersect (Figure 4 point a).
Figure 4 - Circle indicating the potential location of the GPS with two satellite signals.Figure 4 (corresponding to the intersection of the first two spheres). Figure 5 - Potential locations of the GPS receiver with 3 satellites signals (b) Most of the time one of these two points is absurd and is rejected by the receiver that is then able to give the exact location.8:19 A9/P9 1.3 Sources of GPS signal errors Even if today's GPS receivers are extremely accurate, certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. If most of the sources of error are unavoidable, it is important for the user to be aware of the ones that he can influence and be prepared to take steps to reduce their impact.09/25/02 There may also be sources of signal multipath (i.e on Figure 8) occurring when the GPS signal is reflected off these objects before reaching the receiver.
This increases the travel time of the signal and creates errors of distance estimation between the satellite and the receiver.CHAPTER 2: WHY USING GPS IN THE CONTEXT OF THE WHO WHS? The first 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 important investment (many GPS receivers are inexpensive, GPS data is free, and survey staff can be trained quickly to their use).8:19 A9/P9 CHAPTER 3: THE GARMIN ETREX UNIT The Garmin eTrex GPS receiver has been chosen for the WHO WHS because it is easy to use and inexpensive. Its utilisation in the context of different surveys operated in the field has proven its suitability for this kind of work.Depending on the GPS provider the POWER, PAGE and ENTER buttons are not identified with the same symbols as the ones reported on the Figure 9 but as follow.Table 1 - Description of the different eTrex components shown on Figure 9 and 10 GPSfieldguide This antenna allows the receiver to track satellites signals. Thus, when using the GPS, the unit should be parallel to the ground and facing upwards.
Apart from the cover of the holster nothing should be put on this part of the unit as this may stop satellite signal.09/25/02 GPSfieldguide 8:19 A9/P9 3.2 Utilisation of the eTrex unit This section presents the major elements that will be used in the context of the WHO WHS. It introduces you to the basic features of the eTrex as well as some basic definitions of terms in a more detailed way than presented on the Quick Reference guide.WHS we will only need to use two of them: - The 'NORMAL SKYVIEW SATELLITE' page - The 'MENU' page. Figure 12 - The 4 Main pages of the Garmin eTrex GPS receiver Following is the description of these two pages.
Garmin Gps Tutorial Video
Gps Pdf Download
3.2.3.1 The 'NORMAL SKYVIEW SATELLITE' page As mentioned earlier this main page is the first one appearing after the 'WELCOME' page.09/25/02 This information concerns: - The Status of the device. Two type of messages can appear: a) 'WAITLOCATING SATELLITES' indicating that the receiver is tracking satellite signals.
B) 'READY TO NAVIGATE' indicating that the receiver has found satellite signals strong enough to know its location and that you can start to use it. The location accuracy message that is displayed when the device is ready to be used ('ACCURACY').09/25/02 GPSfieldguide 8:19 A9/P9 You can access to these two pages by pressing the ENTER button from the 'NORMAL SKYVIEW SATELLITE' page in order to open the 'OPTIONS' window. From there you can use the UP and DOWN buttons to highlight the page you want to access and press the ENTER button.(represented as a numbered square) around your location (the point at the centre of the screen). In the Figure 16, the GPS device is surrounded by 9 satellites, 7 of them have a signal strong enough to be received (square in black) one (in grey) having a signal not strong enough and the last one not being read by the device (the n°20).09/25/02 GPSfieldguide 8:19 A9/P9 Figure 17 - The 'MENU' page There are two options of interest for the WHS 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.8:19 A9/P9 The 'MARK WAYPOINT' option page Once the GPS receiver has been set-up and that the user has found an open area for the reading, this page will allow the user to visualise his location (Figure 19). The other information or options reported on this page will not be used in the context of the WHS.(Figure 21).
How Gps Works
Press the ENTER button again in order to save the change. The variance field cannot be change, this value is given by the GPS unit and connected with the Earth's magnetic field variation.- Go outdoor for the receiver to catch satellites signal (as the GPS unit cannot receive the satellite signals when you are indoors.) 2. You are not indoors and you are close to the open place where you turned the GPS on (less than 800 km): - Press the UP/DOWN buttons, - Highlight 'NO' - Press ENTER.09/25/02 - eTrex then asks: 'IS TODAY dd-mmm-yy?'
Two possibilities: a) The date indicated matches the current date: Press UP/ DOWN buttons Highlight 'YES' and press the ENTER button, the eTRex will continue tracking satellites and switch to the Satellite page.09/25/02 GPSfieldguide 8:19 A9/P9 4.6 eTrex does not display the local time in the 'SETUP' page The eTrex operates on universal time (or GMT, Greenwich Mean Time ). It is not necessary to have your local time displayed. Do not worry about a wrong displayed time.Dilution of Precision (DOP): The dilution of precision (DOP) is an indication of the quality of the results that can be expected from a GPS point position.
It is a measure based solely on the geometry of the satellites in the sky.Lowrance Electronics GPS Tutorial: Mercator GPS Systems, The GPS Tutor: The Aerospace Corporation: Trimble GPS Tutorial and Glossary: University of Colorado: Smithsonian National Air and Space Museum, Washington, GPS: A New Constellation GPSfieldguide 8:19 A9/P9.