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MIT 12 215 - LECTURE NOTES

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112.215 Modern NavigationThomas Herring ([email protected]),MW 11:00-12:30 Room 54-820Ahttp://geoweb.mit.edu/~tah/12.21512/09/2009 12.215 Lec 22 2Summary of Last class• Satellite Orbits• Treat the basic description and dynamics of satelliteorbits• Major perturbations on GPS satellite orbits• Sources of orbit information:– SP3 format from the International GPS service– Broadcast ephemeris message• Accuracy of orbits and health of satellites212/09/2009 12.215 Lec 22 3Todayʼs class• Basics of Handheld GPS– Run through typical screens that are available inhandheld GPS– Navigation screens– Tips on using this type of GPS12/09/2009 12.215 Lec 22 4Garmin Receivers• This is the brand we will usein our “field trip” next week.• At left is the Garmin V (wewill also use a Garmin III.• Both receivers work either in“portrait” or “landscape”mode• Set by pressing and holdingthe page button312/09/2009 12.215 Lec 22 5Basic Screens• Start up screen when receivers starts• The satellite constellation it shows depends on the last almanacs that wedownloaded and where it thinks you are located• Pressing menu allows user to graphically select location• Height of bars denotes signal strength and solid bars indicate that thesatellite can be used for positioning (i.e., the ephemeris for the satellitehas been downloaded).12/09/2009 12.215 Lec 22 6Map screens• Page and quit cycle through the screens. After the receiver has lockedup on satellites and has a position, the map screen appears• The menu button allows the features of the map to be changed.• The screen below is when the receiver is in navigation mode and isgiven directions on where to go.• When you get close to a turn, the map changes to a detailed view of theturn. In and Out control the zoom on map.412/09/2009 12.215 Lec 22 7Map step up screen• The map setup screens allow of great deal of controlof the appearance of the maps.• The top menu line (moved with the rocker pad) letsdifferent parts of the map be changed.12/09/2009 12.215 Lec 22 8Position page• This page displays basic position and motion information• The bearing shown is the direction of motion relative to true North.(When not in motion, the bearing has no meaning in this receiver. Othermodels has built in compass which will show a direction that receiver ispointing.• Magnetic bearings can be calculated (with out the compass) using a builtin model for the magnetic field)512/09/2009 12.215 Lec 22 9Turn-by-Turn guidance• This receiver will automatically compute routesbetween where you are and a selected location.• These give street names, the distance to the point andthe expected time to arrival (times are based on thespeed limits on the roads)12/09/2009 12.215 Lec 22 10Pointer guidance system• These screens appear when direct path navigation isused (i.e., when roads are not being followed).• Again directions here are for the motion, not thedirection the receiver is facing.612/09/2009 12.215 Lec 22 11Main Menu/Mark• The main menu is obtained by pressing menu twice.• Option below is to mark a waypoint (also appearswhen the enter button is pressed on the map screen).12/09/2009 12.215 Lec 22 12Main Menu/Find• The find screen allows different methods of finding alocation• This screen also appears when goto pressed from themap screen,712/09/2009 12.215 Lec 22 13Setup menu• This menu allows main features to be set. If working with papermaps for example, the datum should be set correctly. UTMcoordinates can be specified as well for maps.• There is also the accessories menu• On and enter at same time shows the test screen12/09/2009 12.215 Lec 22 14Other inexpensive hand helds• Garmin emap ($250): This model is less expensivethan the GPS IV. It has computer connector andexternal antenna co-axial cable connector812/09/2009 12.215 Lec 22 15Magellan receivers• Low costMagellanreceivers12/09/2009 12.215 Lec 22 16Magellan 330 Map• Magellan also makes GPS units with maps:912/09/2009 12.215 Lec 22 17Car Navigation Systems• Many of these systems now available as stand-aloneand built in options.• Most speak and interact through touch screens.• Operation is intuitive with questions such as “Where to”and options like “faster time”, “shortest distance”, and“off road”.• Because detailed maps are built in there are usuallyno map datum options.12/09/2009 12.215 Lec 22 18General considerations withhandhelds• With newer models look for WAAS capability. This isFAA wide-area augmentation system which duringdaytime should improve accuracy of the receivers.• There are quite a few web sites that review GPSreceivers and these can be consulted for guidance• In general when using hand held receivers try to startin a location with good sky visibility• Most of the receivers have many features and soworking your way through the menu options can takesome


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