Page 1 of 11 GEO 465/565 Lab 5 – GPS Data Collection & Mapping Collecting Waypoints in the Field This exercise is designed to familiarize you with several key features of a standard consumer grade GPS. Using a Garmin eTrex Legend, you will learn how to: Parts in red are optional Check the Satellite availability to determine which satellites and how many will be available at certain times of the day for your study location. Prepare the eTrex for use including setting its reference coordinate system/datum and changing the Time Zone. Collect and record waypoints in the field representing distinguishable land features (buildings). Download the waypoints from the GPS to the computer and add to ArcView. Checking Satellite Availability In planning a GPS data collection effort, one of the first considerations should be that of determining the number of satellites that will be available for your particular study area on the date and time of day that you plan to collect data. Time of day is important in terms of when satellites are in your area. Depending on your location and the potential for signal interference, ideally, you would choose a time of day to correspond with the maximum number of satellites available and the signal strength of those satellites. We will determine the number of satellites available for our location by accessing this Interactive Satellite Prediction site: http://sirius.chinalake.navy.mil/satpred/ Use these parameters for Oregon State University: • Latitude (degreesºminutes’seconds”) = 44º34’03” N • Longitude (degreesºminutes’seconds”) = 123º16’37” W • Time = [(our current time in Pacific Daylight time) + (??? hours from GMT or UTC (Universal Time) on a 24 hour clock)]. • Altitude = 246 feet (convert this elevation to meters first) • Elevation Mask = 15 degrees 1. Determine which satellites will be available during our class period and note their assigned numbers on the GPS record worksheet. Also look at the graphic representation of each satellite orbit in relation to your stated coordinate location (OSU). To do this, click on the graphic icon of the world for each satellite. 2. Enter different times of the day and determine when, in a 24 hour period, the most satellites would be available for our coordinate location (OSU). Note this on the GPS record worksheet as well. Page 2 of 11 1 Field Procedure Summary Each field group (2 students) should have a GPS unit and a GPS record worksheet. With this equipment, each group should assemble in the parking lot east of Wilkinson Hall and initialize the eTrex GPS units for use. We will be creating the digital information on OSU support buildings which were not include in the official campus map but play an important role in academic life at OSU We will be collecting waypoints to delineate the outline of Kelly Engineering building, the new COAS building (outlined in the parking lot adjacent to Wilkinson with flags), the Environmental Lab addition to Burt Hall, Fung's Maple Garden, and one waypoint apiece for the Beanery and Subway. Note that we may have 10-12 satellites in our region if the horizon is clear of buildings and trees, etc. But as we will be collecting waypoints adjacent to buildings, we should expect some degradation in the number and strength of the satellite signals. Note that the positional accuracy of these units is <15 meters (49 feet) without any Differential or WAAS augmentation. We have been able to accuracy readings of 14 feet with these units. The key is to stand at each data location long enough to track a sufficient number of satellites. Each group will record the following data for each waypoint collected as per the GPS Record Worksheet format shown at the end of these instructions: Date/Time Group members (and number of GPS receiver) Coordinate System and Datum used to mark the waypoints WAYPOINT ID as displayed on the receiver for each waypoint you collect The latitude, longitude and elevation for each waypoint you collect Accuracy information (in feet) as displayed on the Map page Attribute information that will be entered into the attribute table for each point (waypoint) when it is converted into a shapefile in ArcView. Note the following information for 2 different attributes: Cardinal direction for corners of building, using the compass to determine the direction; and the name of building. Detailed Instructions: NOTE: Words in [BRACKETS] refer to either individual buttons on the sides of the receiver or the round Click Stick on the receiver face. Note that the [CLICK STICK] allows you to move up/down or right/left to move through menu options, highlight fields, on-screen buttons, icons, enter data or move the map panning arrow. Although there is only one physical Click Stick, pressing the top, bottom, left or right portion of the key will result in the appropriate cursor movement, designated with these symbols [↑][↓][←][→]in the instructions. Words in UNDERLINED CAPS refer to menu options that appear on the receiver's screen. Use the [CLICK STICK] [↑][↓] movement to scroll up/down a list and highlight an option. Press in on the [CLICK STICK] to select a highlighted menu option. In these instructions, “select’ would mean to highlight an option and press in on the [CLICK STICK] to select that option. Words in CAPS refer to data fields or screen titles. If you press and hold the [CLICK STICK] for at least two seconds this allows you to mark your current location as a waypoint. Page 3 of 11 To exit out of any menu, use the [CLICK STICK] [←][→] to select the on-screen “X” button (in the upper right corner) and then press in on the [CLICK STICK]. Initialization in the lab 1. Power up the GPS unit 1.1. To begin, press and hold the [POWER] for a few seconds to turn the unit On/Off. Read the warning message and then view the SATELLITE page. CHANGE THE MODE SO THAT THE UNIT IS NOT USING THE SATELLITES. 2.0 Clear any previously stored Waypoints from receiver memory: 2.1 In the MAIN MENU, Press [FIND] to access any previously collected waypoints. 2.2 Select WAYPOINTS and then select NEAREST (you will see a list of any previously stored waypoints that are nearest your current location). 2.3 Select the OPTIONS MENU (the page icon at the top right of the screen) and select DELETE ALL. At the warning "Do you really want to delete all waypoints?” – select YES. This will delete any previously stored waypoints that are near to your current location. There may still be some GARMIN factory stored waypoints that are not deleted. 2.4 Press [PAGE] to return to the MAIN MENU. 3.0 Set the correct Time Zone for our location: 3.1 From the MAIN MENU, select SETUP and then within this submenu, select the TIME option. 3.2 The following parameters should be set in this menu: 3.2.1 Time format = 24 (hour time format) 3.2.2 Time Zone = US Pacific 3.2.3 UTC Offset = -08 hrs 00 min 3.2.4 Daylight Savings Time = Auto 3.3 Select the on-screen “X” to exit out of this sub menu and return to the SETUP MENU. Note that you may need to press [PAGE] several times to get this menu. 4.0 Set the Position Format (coordinate system display) and Datum 4.1 From the SETUP MENU, select the UNITS option 4.2 The following parameters should be set in this menu: 4.2.1 Position Format = hdd°mm.mmm' 4.2.2 Map Datum = WGS84 4.2.3 Distance/Speed = Statute 4.2.4 Elevation = feet 4.2.5 Vertical Speed = ft/min 4.2.6 Depth = Statute 4.3 Select the on-screen “X” to exit out of this sub menu and return to the SETUP MENU. 4.4 Press [PAGE] several times to return to the SATELLITE page. 5.0 Change the default elevation to a more accurate reading 5.1 From the SATELLITE page, select the OPTIONS MENU from the top right part of the screen. 5.2 Select NEW ELEVATION and manually enter the elevation in feet for Corvallis (246 feet), using the [CLICK STICK] to highlight the desired numerals and then pressing the [CLICK STICK] in to select that number. Select “OK” to complete entry. Press [PAGE] several times to return to the SATELLITE page Page 4 of 11 Collecting waypoint positions for features in the Field 1. IN THE FIELD 1.1. In the field, when you have your GPS units powered up wait for enough satellites (want at least 4 satellites) to provide a 3D GPS Solution before continuing. You are now ready to navigate. On the Satellite page, check the relative signal strengths of the numbered satellites from step 1. Also note where, within the Skyview graphic on the receiver, these satellites are located. The inner ring represents a view above you at a 45° angle from vertical, whereas the outer ring represents the horizon and the center represents directly overhead. Hint: you will have to stand in one place with the GPS unit away from your body for a few minutes to get a sufficient number of satellites with strong signal strengths. This should be your standard method of data collection for each of your data points. Don’t rush the collection of data as your accuracy readings will be very poor. 2. RECORDING WAYPOINTS 2.1. To record the receiver's current position as a waypoint: 2.1.1. From the SATELLITE page, position the GPS receiver near the feature location you want to mark. Wait for a sufficient number of satellites to be tracked and a low enough value for the accuracy reading (± 20 feet is desirable and lower is better).