Names in the Field: A Simple GPS Field Exercise
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
This exercise is a field lab to introduce students to basic methods of GPS data collection, uploading the data to a computer, and making simple maps of their data using GIS software.
Concepts of data resolution (error), and sampling techniques are introduced as the students try to spell words in a field using the "track" (or "breadcrumbs") collected by the GPS unit.
- Learn to use a consumer-grade, handheld GPS unit to collect data
- Upload GPS data from GPS unit to a computer
- Create a map of the data using GIS software (or Excel)
- Consider instrument error (or resolution) and sampling rates
- Plan field observations (GPS data collection) in a way to meet the stated objective (to spell recognizable words) given the error and sampling rate restrictions
Context for Use
This is a field lab exercise that requires the students to work outside in an open field with good view of the sky (few trees or buildings). A campus quad with few trees or an unoccupied athletic field roughly 100 ft x 200 ft in size is all that is necessary. It doesn't matter whether the field is flat or hilly.
This lab can be run early in the semester as an example of field data collection. It can also serve as a primer for students to learn to collect GPS data before using the receivers during subsequent geology lab exercises.
There should be one GPS receiver for every 2-4 students so each can take a turn navigating the user interface and see the recorded data.
The students usually require 10-15 minutes to become accustomed to the GPS interface once they understand the button functions. It is important to encourage them to move around as they familiarize themselves with the system so they can get a feel for the scale of the map display on the screen.
GPS Field Exercise (Microsoft Word 35kB Mar24 05) - a sample hand-out that could be used for the collection of GPS data in the field. The last two items (higlighted with formatted text) can be edited depending on how the data will be downloaded from the GPS receivers and presented to the students. This exercise assumes the use of Garmin handheld GPS receivers.
GPS Exercise - Upload GPS Shapefiles (Microsoft Word 28kB Mar24 05) - a sample hand-out that can be used to have the students upload the GPS data as ESRI shapefiles into ArcView and edit them to create maps of the elements they traced in the field.
GPS Exercise - Upload GPS Text Files (Microsoft Word 26kB Mar24 05) - a sample hand-out that can be used to have the students upload the GPS data as text (ASCII) files into ArcView and edit them to create maps of the elements they traced in the field.
Teaching Notes and Tips
Most students are able to figure out consumer-grade GPS units if they're familiar with modern cell phones. It is best to discuss how GPS works before heading outside to record data. This will help the students understand what controls position accuracy.
This exercise can lead to discussions about precision (repeatability) and accuracy of measurements. By tracing out letters in a field the students must consider the accuracy of their data points as the consider how large the letters must be in order to be recognizable. Have them consider the "accuracy" of writing with a large-tipped marker. How large must the letters be to be legible given the width of the pen tip?
Depending on the number of students in each group, the field exercise should take about 1.5 to 2 hours. If the field is very large, the students may take longer.
Bring spare batteries for the receivers to the field! Most receivers will retain existing data while batteries are changed.
Accuracy is greatly improved by using GPS receivers that are "WAAS-enabled" and an external antenna. See Using GPS in Geoscience Education for more information
Depending on time available, the instructor could do any of the following:
- have the students download the data from the GPS receivers if cables and computers are available. The MN DNR freeware GPS tool for Garmin GPS receivers is quite useful.
- download the GPS data outside of class and provide text (ASCII) filesfor the students to load into GIS software. Editing the text files can be time-consuming and confusing for the students, especially since minor spelling errors (or leaving Excel open while importing into ArcView) can cause the import to fail.
- download the GPS data ouside of class and provide ESRI shapefiles to the students to load into the GIS software. Exporting to shapefiles will speed things up, but the students (or the instructor) will have to merge any breaks in the tracks caused by signal losses.
- use other GIS/GPS software to create maps of the student data
- create plots of the tracks using the GIS or GPS software outside of class and provide them to the students to complete the exercise.
If the students will upload text (ASCII) files, they will need to convert the points to polylines. ArcView does not have a simple way to do this. Go to http://www.ian-ko.com/ (more info) and download the ETGeowizards package for ArcView 8.x (or for ArcView 9.x, depending on the version of your GIS software). Install the program and load the tool into ArcView by following the instructions in the README file. The students can do this as part of the exercise, but check that they have installation permissions on the classroom computers.
Assessment is based on the ability of the students to collect meaningful GPS data in the field, upload and edit the data in ArcView, create a map of their data, and create a report of their observations and results.
The sample hand-outs have simple questions that can be modified to increase the level of analysis of GPS position errors. Likewise the level of detail and information in the final maps (e.g. scale-bar, North arrow, grids, projection information, etc.) can vary depending on the level of GIS competency in the class. Providing a georeferenced airphoto (e.g. downloaded from the Terraserver site - detailed instructions) can help the students see the spatial context of their measurements.
References and Resources
Using GPS in Geoscience Education - basic ideas for using GPS in education, including list of vendors
MN DNR shareware extension for Garmin GPS downloads. (more info) -- Works as ArcView extension or stand-alone Windows application. Data can be imported into a variety of projections and exported to text files or ESRI shapefiles.
ETGeowizard Tool (more info) - a convenient shareware plug-in tool for ArcView 8.x and 9.x that will convert between differnt types of shapefiles (e.g. points to lines, lines to polygons, etc.) as well as numerous other features that are not readily available in ArcView.