USDA APHIS | Home Landing Page



Use of a Standard GPS Receiver to Determine Latitude and Longitude Coordinates The Garmin eTrex Legend H is currently the standard GPS receiver recommended for use by APHIS:Veterinary Services and partner organizations. This document contains information on how to use this standard GPS receiver. The Garmin eTrex Legend model H receiver replaces an earlier model, the Garmin eTrex Legend, as the GPS receiver recommended for Veterinary Services field staff for all types of investigations. The eTrex Legend H uses a USB cable to connect to a computer; whereas, the older eTrex Legend model required a serial port cable. Serial ports are no longer found on most laptop computers. In addition, the Model H has improved response times, greater sensitivity under a tree canopy, and increased accuracy. How to Obtain Latitude and Longitude (Lat/Lon) Coordinates for a Location Using the Garmin eTrex Legend H GPS ReceiverThe following instructions are based established field protocols for the Garmin eTrex Legend H GPS receiver (Figure 1). Specific techniques will vary slightly depending on the GPS receiver model being used. Figure 1. Garmin eTrex Legend H GPS ReceiverInitial SetupAlways setup your GPS receiver, before using it for the first time, by following steps 1 – 12 shown below. If the preferences or setup options are inadvertently changed, it is important to rerun this initial setup procedure.Turn the GPS receiver’s power on by pressing and holding down the POWER button for 2 seconds (lower button on right side of the unit). When the Satellite page appears on the screen, press the Page button on upper right side of the receiver several times to scroll through pages until you reach the Main Menu page.The rocker key, or toggle button, on the front of the receiver can be used to move up, down, left, and right on the screen. When an item is highlighted, pushing down on the rocker key (i.e., towards the bottom of the receiver) will select a highlighted item and make it available for further action. On the Main Menu page, use the rocker key to highlight and select the Setup option. This will open the Setup Menu page.Highlight the Time icon and select it to open the Time page. Check that the correct time zone is selected. If not, highlight this option select it by pressing the rocker key. A drop-down menu will appear. Use the rocker key to highlight and select the correct time zone. Change Daylight Saving Time to Auto, if this option is appropriate for your location. No other changes need to be made on this page.Press the Page button (upper right side of unit) to return to the Setup Menu page.Highlight the Units icon and select each option with the rocker key. This with open the Units page. Highlight and set the following preferences:Position format—hddd.dddddMap datum—WGS 84Distance/speed—StatuteElevation/Vertical Speed —Feet (feet/min)Depth—FeetPress the Page button (upper right side of unit) to go back to the Setup Menu page.Highlight and select the System icon to open the System page. The GPS option should be set to Normal.Scroll down to WAAS/EGNOS (Wide Area Augmentation System) option and select Enabled. EGNOS is a system similar to WAAS, but covers Europe and neighboring areas.While in either the Setup Menu or the Main Menu pages, check the battery power icon located in the upper right corner of the either menu page to make sure that battery power is at the full level (i.e. four bars shaded in the battery icon).Press the Page button (upper right side of unit) to exit the Setup Menu and then again to exit the Main Menu. If necessary, continue to press the Page button until you return to the Satellite page.Setting Up an Accuracy Check Point (ACP)The purpose of an Accuracy Check Point (ACP) is to ensure that setup options for a GPS receiver have been set correctly to the VS standardized format (see Initial Set Up) and to confirm that a receiver is in a satisfactory working condition. The ACP should be located near your office, or home base, and should be in a location that is convenient for you to check your GPS receiver before going to field sites. The steps in establishing and ACP are: Choose a specific location that is away from trees, buildings, or other objects that may block a clear view of the sky. Do not choose a light pole, telephone pole, flag pole or other tall objects. An ACP should be a stationary, flat surface that is easily recognized and one on which you can place your GPS receiver for a few minutes while a unit locates satellites and determines the receiver’s location. In establishing an ACP it is best to either a) Use at least two or more GPS receivers to compare coordinates or b) make three or more observations with one receiver at different times during the day. Acceptable accuracy is when geographic coordinates for an ACP match three places to the right of the decimal. The last two decimal degree numbers displayed are more variable and represent differences of only a few feet.As a reference to help confirm that a GPS receiver is performing properly, it is best to display (e.g. laminated card) ACP geographic coordinates on or near the ACP location.Regular Confirmation of Receiver AccuracyCheck the accuracy of your GPS receiver each time before going into the field to ensure it is set up properly and working correctly:At your ACP location, power-on your receiver and wait until the estimated accuracy is 25 or fewer feet (8 meters or less). Then obtain ACP coordinate observations and compare these values with the numbers on your ACP reference card. If the accuracy the values do not agree for the first three numbers after the decimal, return to Setup Menu and confirm that the setup options have been set correctly. Reporting Latitude and Longitude Coordinate Data Acquired with a GPS ReceiverWhen standing at a specific location for collecting geographic coordinates (e.g. premises front gate/driveway entrance, or other locations according to VS standards), press the rocker key downward (vertically) and hold the key until the Mark Waypoint page opens. An alternative is to use the Page button to navigate to the Main Menu and Select Mark. When Mark is selected a new Waypoint Page is created with a new number. Record the waypoint number, or change the name of the waypoint to one that will be easily recognized.With the rocker key, scroll to the bottom of the waypoint page and select Avg to average a series of waypoints that are being collected automatically. After collecting and averaging 20 or more waypoint values, select Save to store the averaged waypoint value and select OK to exit the Waypoint page.To view the latitude and longitude results of a geographic location, go to the Main Menu page and select Find and then select Waypoints. Locate the waypoint number or name in the list of waypoints stored. Select the waypoint you wish to view and select it with the rocker key. Record the geographic coordinates shown in the Location box on this page. On your data form, always record all six decimal places as in the Location box.It is always a good practice to transfer latitude and longitude coordinates from a GPS receiver to a personal computer for inclusion in reports, using a data cable and transfer software such as the open source application DNR Garmin (). Hand transcription of coordinates directly from a receiver’s waypoint page to a data form increases the likelihood of errors. Errors in geographic coordinate data can have significant negative consequences; therefore, errors, even small ones, must be avoided.Do not record geographic coordinate data from the Satellite page. The numbers shown in the Satellite page are highly variable and are likely to be less accurate than those from the Waypoint page, especially ones that have been averaged. Standards for GeodataThe following are the standards for geodata:Coordinate dataLongitude (X) and latitude (Y) coordinatesDecimal degree (hddd.ddddd) format Minimum of five decimal places to be reported on data formsMinus sign (–) to indicate west longitudeDatum reference to use is World Geodetic System 1984 (i.e. WGS 84)No projection (geographic data on data forms should always be unprojected with a reference datum of WGS-84). In GIS applications, no projection is sometimes referred to as the Geographic Coordinate System, or GCS.Tabular (database) dataDatabase file (DBF IV) Microsoft Access Database Comma-delimited text file (CSV, TXT)Vector data formatEnvironmental Systems Research Institute (ESRI) shapefile format (*.SHP) ESRI ArcInfo coverage format Image (raster) data formatGeoreferenced JPG, or JPG2000 (Georeferenced means that a world geographic file is associated with an image.)ESRI ArcGrid American Standard Code for Information Interchange GeoTIFF Multiresolution seamless image database (MrSID)Non-georeferenced Tagged interchange file format (TIFF)JPEGGIS data file compressionWINZipMrSIDStandardized Locations for Collecting Latitude and Longitude Coordinate Data for Confined Animal PopulationsPremises—front gate, defined as the driveway entrance where you leave public access (Note: This location is essential for data forms. An animal’s location should not be used as a substitute for premises locations. It is also important that a data form include a street address and zip code that can be used to confirm GPS premises observations. Do not use P.O. box numbers in listing an address on a data form.Animal location depends on species or commodityGate entrance to a pen or facility where the animals to be mapped are locatedDairy—milk parlor entrancePoultry or swine—feed mixing areaPasture—gate entrance to the pastureLocations for collecting coordinate data of free ranging populations, including wildlifeDaytime—estimated home range based on landscape factorsNighttime—if not on range, the pen or corral where the animals are held at night.Note: In the United States, north latitude is positive and west longitude is negative and a minus sign must be added to the longitude coordinates when they are being reported. ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download