Global Positioning System (GPS) Tools

The Garmin eTrex GPS Unit

1.0 The Basics

The Global Positioning System (GPS) is a collection of satellites operated by the U.S. Government. GPS tools, such as the Garmin eTrex equipment demonstrated in class, can be used to:

• Determine location in latitude/longitude units ( +/- 5 meters )
• Name and store location(s) in memory
• Determine altitude
• Calculate speed, direction of movement, distance or transit time between locations, etc.

GPS tools are commonly found in cellular telephones and car navigation systems. By communicating with a minimum of 3 satellites, GPS equipment can calculate its location via geometric triangulation. The capabilities of GPS equipment are made even more powerful by integrating the tools with mapping software, such as Google Earth.

2.0 Key Features

The Garmin eTrex GPS equipment is battery-powered and hand-held. To turn the eTrex on, press the PWR button on the right side of the unit. The equipment will immediately begin to access satellites.

2.1 The Satellite Page

The first page you will see after powering the unit on is the Satellite Page. This page shows the status of communications between the eTrex and available satellites. The eTrex must be communicating with at least 3 satellites to determine its location. Place the unit in an area that is away from large trees and buildings for best results.

2.2 The Navigation Page

From the Satellite page, press the PAGE button on the upper right side of the unit to toggle to the Navigation Page. The Navigation Page looks like a compass with data displayed at the bottom. This page can be used to determine your location and guide you to another location. To determine your location, press the UP arrow on the left side of the unit until latitude and longitude are displayed at the bottom of the compass. The latitude and longitude readings will change as the equipment is moved between locations.

2.3 The Waypoint Page

The Waypoint Page is used to store location information for future use, including automatic uploads to mapping software. The term “Waypoint” is used to describe the coordinates of a stored location. In order to save or “mark” a Waypoint:

(1) From the Navigation Page, press the PAGE button at the upper right side of the equipment to switch to the MENU page.

(2) Press the UP Button on the left side of the unit to highlight the MARK field.

(3) Press the ENTER button on the left side of the unit. THe MARK WAYPOINT page will appear, with “OK?” highlighted. Press the ENTER button again to confirm.

3.0 Applications, Limitations, and Insights

GPS tools present numerous applications for inquiry-based science and specifically for our science camp this summer. In terms of data collection, the GPS tools can be used to mark data collection points which can then be superimposed in Google Earth or other map software to provide a visual map of your data collection points. This map could be used to look at elevations, the environment surrounding your points, and to provide a clear picture for a presentation or report. Another useful feature of GPS tools is the ability to calculate distance between two points. There are times that terrain would make any direct measurement of distance difficult or impossible but the GPS tool can calculate this distance without regard to terrain. However, there are times that doing this could be more difficult, time consuming, and costly than simply using a direct measuring device (such as a tape measure, trundle wheel, or meter stick). GPS tools can be used for navigation purposes or used to determine elevations. These devices can also be used to teach students orienteering skills, familiarize students with compass directions, and provide an application for converting between different coordinate systems. However, there are times and students for whom using a GPS device might be impractical or obscure the actual concepts. Some people are intimidated by technology and therefore can get so anxious or frustrated with the technology that they don’t learn the underlying content. GPS tools are also expensive (~$100 each) and potentially not accessible to all students. Students might require much more guidance with a GPS tool, decreasing the self-reliance piece of an inquiry investigation when a more simple tool like a tape measure might allow students a higher level of comfort and more independence.

4.0 Warnings and reminders to ensure efficient use:

1. Be in an open area outside with no overhead obstruction to ensure the tool will pick up the satellites
2. Make sure the latitude/longitude coordinates are in the format you desire (minutes vs. decimal places)
3. Train the user thoroughly before use
4. Directed instruction/activity is necessary in order to utilize the tool in a way that makes it effective verses a distraction
5. Bring extra batteries
6. Know what you will do with the data you have collected