Lab Exercise: Getting GPS Data into QGIS

Transcription

1 Lab Exercise: Getting GPS Data into QGIS Author Attribution Major contributors to this curriculum include (alphabetical): Lara Aniskoff Dennis Babaasa Maria Fernandez Michael Hamel Quentin Lewis Maili Page James Peters Charlie Schweik Alexander Stepanov Module Licensing Information Version 1.0. This tutorial is licensed under a Creative Commons Attribution-No Derivative Works 3.0 License ( This means that users are free to copy and share this material with others. Requests for creating new derivatives should be sent to the primary author. Reviewed by This exercise is QGIS v1.6 compatible Introduction: Once you ve collected field data with a GPS, you often want to get that data mapped as a point, line or polygon GIS layer. There are a couple ways to do this: 1) You can map your GPS points using an ASCII delimited text file ; or, Or, if you have a downloading cable and a way to connect to your computer, 2) You can download your GPS data directly to the computer using a GPS downloading cable. In the Holdsworth 302 computer lab, we can t easily download from the GPS, because we can t hook up a downloading cable. IN THE LAB, WE WILL DO PROCESS #1, GIVEN WE CAN T USE A DOWNLOADING

2 CABLE. However, if you use one of the department GPS for your project, we will arrange it such that you can use technique #2 if you d like to. Technique #1: Map your GPS points using an ASCII delimited text file For this exercise you ll need to get the UMass 1999 orthophoto from MassGIS. The tile number you want is In this example, we will map the geocache locations we gave you for the geocaching lab. 1. Recall what coordinate system and datum you collected your data in. What was the coordinate system of the geocache points we gave you? What was the datum? 2. Create a folder on your computer for your work (C:/temp/gps) 3. Enter these points into an ASCII text file editor. What is ASCII? It stands for American Standard Code for Information Interchange, and it is essentially standard codes for the numbers 0-9 and letters A- Z (and a few special characters). ASCII editors simply store these characters and nothing more. This is compared to wordprocessors like MS Word which store all sorts of underlying codes that you don t see (for example, when you bold some text). In Windows, the ASCII editor is NOTEPAD (Start, Programs, Accessories, Notepad) Open Notepad Enter a heading line and then the information on your points. These are the headings of your file, and each are separated by commas. We re creating what is called a comma delimited text file. Here you can enter your attributes related to your points as well. In this case, we are entering the Lat\long locations, the cache name, the accuracy of it when we collected it, and a text field for some comments. Enter: Lat, Long, cache, accuracy, comments , , cache1, 22ft, three granola bars left , , cache2, 22ft, one granola bar left

3 , , cache3, 23 ft, two granola bars left IMPORTANT: WHY DO I HAVE A NEGATIVE SIGN IN FRONT OF THE 72? In the Long/lat system, the western hemisphere is negative. On the GPS it said 72 degrees WEST. But in this system we have to tell the computer west by specifying a negative sign. If we had entered a positive 72 we probably would wind up somewhere in Europe or Asia Save the ASCII file to your computer (c:/temp/gps). Call it geocache_pts.txt 4. Start QGIS 5. Settings, Project Properties set it to the coordinate system and datum the GPS points are in. These were: Geographic coordinates (Long/Lat), datum NAD Plugins, Manage Plugins. Click on Add Delimited Text Layer. 7. A new icon for adding a delimited text layer appears on your QGIS menu 8. Press it. The Add Delimited Text Layer screen appears.

4 9. Press browse and navigate to your file (c:/temp/gps/cache_pts.txt). You will probably need to specify which column is the X field and Y field. In Long/Lat coordinates, Longitude is the X and Latitude is the Y. Enter a comma (,) in the Delimiter field, and click the Parse button. 10. Click OK 11. Your QGIS map should look like this: 12. Set the coordinate system for this new layer. Right click on the cache_pts in the table of contents, choose Properties, General tab, Change CRS button. Set it to Geographic Coordinates, NAD83 datum Change the color of the points to yellow. 13. Save or output this layer as a shape file. Right click in table of contents, Save as shape file. Name it c:/temp/gps/caches_long_lat.shp. In the projector selector, choose geographic coordinate system and choose NAD83 as the datum. You should get a message saying the shape file was created. 14. Create a new QGIS project using the UMass orthophoto and see how accurately our locations are mapped. Note that in this exercise the orthophoto from MassGIS is in State Plane projection, NAD83 datum, and your GPS point shapefile is in Geographic Coordinates, but also NAD83 datum. (Having them in the same datum helps QGIS doesn t have to convert them) File, new project, discard current project - yes. A new blank QGIS project will appear Specify in project properties the coordinate system (State Plane, NAD83) so choose Lambert Conformal Conic, Massachusetts Mainland.

5 Also, click enable on the fly CRS projections to on. 14. Add the UMass orthophoto raster. Right click on the table of contents entry, properties, general tab, change the coordinate system to State Plane (Lambert Conformal Conic, NAD83). 15. Add the vector layer of geocache locations. C:/temp/gps/caches_long_lat.shp). Your QGIS screen should look like the below (notice the three points mapped): But yours will be yellow. Assignment Deliverable: Please upload the image to the Spark course web page. Please include any problems you may have come across. (Create the final layout- export as image- add image to Open Office doc, include any problems, Export as PDF-->Submit. Thanks!