GPS Activity Teaching Notes

TIME REQUIREMENT

Approximately two- to three class periods (assuming 60- or 90-minute periods):

Pre-Lab - Learning to use a GPS receiver to find your location (one period)
Lab - Collecting Field Data (one period)
Post-Lab - Analyzing the Field Data to find the Mystery Location (one period)

SAFE-T COMPASS

Pointless (well, that's the point!) drawing compass available from:

Tricon Publishing, Phone: 1-888-224-8053, Item No. AB-668, $1.19 each plus s/h.
Teacher's Discovery, Phone: 1-888-97-SCIENCE, Catalogue No. SGE4, $1.95 each.

BATTERY RECOMMENDATIONS

Eveready Energizer alkaline batteries - Eveready guarantees repairs if batteries damage GPS receiver. (Eveready GUARANTEE: We will repair or replace, at our option, any device damaged by these Energizer batteries.) Since batteries with built-in strength-testers sometimes get stuck in appliances (they are slightly larger in diameter than standard AA batteries), this is an important consideration.

SIMULATOR MODE

Simulator Mode allows you to operate the GPS receiver without acquiring satellites, and is ideal for practicing all aspects of unit operation while indoors. From the MENU Page, move the field highlight to the "OPERATION SETUP" field and press the ENTER key. To select an operating mode:

Move the field highlight to the "MODE" field and press the ENTER key.
Use the up and down arrow keys to choose the desired mode and press ENTER.

By default, the receiver powers-on in Normal Mode.

PROGRAMMING THE MYSTERY LOCATION

Select an off-campus position which will be easy to locate on a large-scale map, e.g., the intersection of two streets. Remember, the GPS receiver is accurate to within 100 meters (330 feet), therefore you should avoid selecting locations which fall below the theoretical limit of resolution. Ideally, the mystery location should be familiar to students and relatively close (but not too close) to the school building, that is within a mile-or-so of the school. Caution: the bearing to more distant waypoints will be very similar (e.g., waypoints in another state).

Once you've selected and acquired a suitable position, mark it as a waypoint for future reference. Press the MARK key to capture and hold your current position. The Mark Position Page appears, showing the captured position and a default 3-digit waypoint name. Change the default name to "MYSLOC".

Press the up arrow key twice to move the field highlight from the "SAVE?" field to the name field.
Press the ENTER key to begin entry of your waypoint name.
Press and hold the up arrow key to scroll through the alphabet until the letter "M" appears.
Press the right arrow key once to move the character highlight to the next character space.
Repeat Steps 3 and 4 until the word "MYSLOC" is displayed.
Press ENTER to complete entry of the name.
Press the down arrow key once to return the field highlight to the "SAVE?" field.
Press the ENTER key to confirm that you want to save the position as a waypoint named "MYSLOC".

The Mark Position Page will be replaced by the page displayed prior to pressing the MARK key (most likely the Position Page).

Ideally, "MYSLOC" should be the only waypoint which begins with the letter "M". If you press the GOTO key, the waypoints field on the Navigation Page does not display the names of all waypoints which begin with the same letter. To see a complete list of waypoints, press the PAGE key repeatedly until the MENU Page is displayed; use the arrow keys to highlight "WAYPOINT LIST" and press ENTER.

FINDING THE MYSTERY LOCATION

Using either a computer and large-screen display or an overhead projector, transparency map, drawing compass, and protractor, demonstrate for the class the three processes which may be used to find the mystery location:

Using three different distance measurements to draw three intersecting circles;
Using two bearing (direction) measurements to draw two intersecting lines;
Using one bearing measurement and one distance measurement to draw a single line which shows the mystery location.

1. Using Distances to Find the Mystery Location

Begin by drawing the three intersecting circles. DeLorme's Street Atlas USA 6.0 software features large-scale, street-level maps and a variety of tools which can be used to precisely locate points on the map using latitude and longitude, measure distances, and draw circles. Refer the the sample maps (below) where this has been done. Given the coarse grid on many maps, students may have difficulty correctly positioning the points, circles, and lines which they will draw on the map. The computer-interactive approach is quicker and more accurate and is preferrable to manually drawing circles on the map.

If you do not have Street Atlas, then students may use washable felt-tip markers or grease pencils to draw on laminated maps such as road maps or topographic maps. [Special note to Fairfax County (VA) Public Schools (FCPS) teachers: high-quality large-scale maps of all FCPS schools are available online at the FCPS Web site. From the directory of schools & centers, follow the hyperlinks to your school and click on the street address. The map scale is 1 inch = 2,000 feet (one inch is the length of the side of one of the squares on the map).]

(Click on graphic to view larger image.)

In a very real sense, finding the mystery location by drawing three intersecting circles (triangulation) is similar to the process used by the global positioning system to determine your location. In fact, guiding students to make this connection should be one of the key points to be made during the post-lab discussion (you may need to refer to a brief review of how GPS works). It is also similar to the technique used to locate the epicenter of an earthquake.

2. Using Bearings to Find the Mystery Location

Street Atlas cannot be used to measure angles, however it can be used to print a hardcopy map of the area surrounding the school on which you have drawn dots to locate Points 1-5 from the Field Data. Align the vertex of a protractor with Point 1; be sure that the 0-degree mark is aligned with true North. Use the protractor to measure the bearing; use a straight edge to draw a long line which extends from Point 1 at the proper bearing (angle). Repeat the process for Points 2-5. You should discover that only two bearing measurements are necessary to find the mystery location.

As a sidebar, you may want to discuss the similarity between this technique for locating the mystery location and the way the National Lightning Detection Network determines the range to cloud-to-ground lightning flashes using at least two bearing/distance measurements to each lightning flash.

(Click on graphic to view larger image.)

3. Using One Bearing and Distance to Find the Mystery Location

Print another hardcopy map of the area surrounding the school on which you have used Street Atlas to draw a dot to locate Point 1. Use a protractor to measure the bearing; use the map scale and a straight edge to draw a line whose length is equal to the distance between Point 1 and the mystery location (refer to the Field Data); the mystery location is at the end of this line segment.

(Click on graphic to view larger image.)

ASSESSMENT

(Strategies used to show evidence that the lesson is effective and meets student learning objectives - to be added. Ideas: rubric; students design orienteering course, successfully navigate course using GPS receivers.)