Using Google Earth for Environmental Science Research
This document is up-to-date as of August 2013. If you have any questions or additions to this material please email [email protected].
Note: this protocol requires you to download Google Earth and additional software. I have never experienced any problems with this software, but you download them at your own risk.
Contents
Introduction………. 1
Using Google Earth………. 2
Using uploaded photos……… 2
Importing your GPS data………. 3
Distances, areas and perimeters………... 3
Creating buffers……… 5
Generating random points……….. 8
Terrain and elevation……….. 11
Using historical imagery to show change through time……… 13
Adding Google Earth imagery to ArcGIS………... 14
Google Earth Pro………. 17
A list of general (free) GIS resources……….. 17
Introduction
I cannot imagine conducting research before the creation of Google Earth in 2005!
Having free, high-resolution satellite data at our fingertips provides us with a new way to conduct our research, and communicate it in a simple and fun way to the public.
However we don’t use Google Earth to its full potential. We may use Google Earth to look at a new study site when we are planning our research, or we may overlay GPS points. But Google Earth offers so many more ways to improve how we do environmental research. This document is designed to be a handy collection of tools and tips to maximize the use of Google Earth in your own research.
Using Google Earth
• You can download Google Earth onto your computer from this website:
www.google.com/earth/download/ge/agree.html.
• A good introduction to the basic use of Google Earth can be found here:
https://support.google.com/earth/?page=guide_toc.cs.
• The Figure below shows the standard layout of Google Earth. The navigation tools are found at the top right. The Places sidebar displays search results and layer that you create (e.g. lines and polygons. The Layers sidebar shows different information such as borders, town names, roads, photos etc. These can be switched on and off.
Using uploaded photos
One great thing about Google Earth is that is designed to be used by the public – some people have said that Google Earth has “democratised” geography. Many people have uploaded their holiday photos etc. onto Google Earth, tagged with the geographical information about where the photo was taken. This huge store of photos is an invaluable resource for researchers. For example, I recently organized a 1-week field course in Thailand for graduate students from Singapore. I have worked in the area
for many years so was familiar with it, but we wanted to travel to a new location to look at how the geology changed. Luckily, I could plan this activity from my office, by looking at tourist’s photos of waterfalls, mountains and quarries to see the geology!
• To access the photos, go to Layers and switch on PhotosàPanoramio
Importing your GPS data
Google Earth can be used to display GPS waypoint and track data that you have collected. This is useful to see where you have been, and is very important for ground- referencing during remote sensing analysis to check for accuracy. E.g. you can take GPS points in different land cover types (e.g. mangrove, coastal forest, terrestrial forest), then see what those land cover types look like on Google Earth.
• On the main toolbar go to ToolsàGPS.
• Select the model of your GPS
• Select the type of data you want to import
• Click import.
• Your waypoints and tracks will appear in the Places sidebar.
Distances, areas, and perimeters
Distance measurements• To measure distances, click on the distance tool:
Area and perimeter measurements
The free version of Google Earth doesn’t allow you to measure the area or perimeter of a polygon. However, other tools are available to do this.
• Click on Add Polygon and draw a shape around the place where you would like to calculate the area and perimeter.
• On the Places sidebar right-click your line/polygon and choose Save Place As…
• Enter a filename and location to save, and save as .kml.
• Download the tool GEPath from www.sgrillo.net/googleearth/gepath.htm Note: This tool is not available for mac.
• In GEPath go FileàOpen KML.
• At the bottom of the GEPath program you can select Calculate perimeter, Calculate area etc. You can also choose the units (e.g. km).
• GEPath uses two slightly different algorithms for small polygons and large polygons. Click Method to choose the most appropriate for your polygon.
• Go Run on the main toolbar and name and save the file. In GEPath it will now display the perimeter and area. It also displays the calculated polygon back in Google Earth.
• You can also do other tasks in GEPath, such as make a path, add a grid to Google Earth etc.
Creating a buffer
The Buffer is a common tool in commercial GIS software. For example, you would like to know how many shrimp ponds are within 1 km of your mangrove. The buffer tool will draw a 1 km line around your site. This tool is not available on Google Earth, but a web tool is available which we can use.
• Click on Add Path or Add Polygon to create a line or polygon.
• It should look something like below:
• On the Places sidebar right-click your line/polygon and choose Save Place As…
• Enter a filename and location to save, and save as .kml.
• Now go to http://extension.unh.edu/kmlTools/index.cfm
• Click Choose File to upload your saved .kml file.
• Enter a description and press Submit.
• Under the Buffer box, enter the size of your buffer. You can choose it in metres, kilometres, feet or miles.
• Click Buffer. A new window will open, with the buffer visualized on Google Maps. It will look like the map below.
• Save the .kml file by clicking on the symbol that is shown above. Then import that into Google Earth. It should look like this:
• Having a thick buffer is not much use at the moment because you cannot see the imagery behind it. So in the Places toolbar right-click the .kml file and select Get Info. Click on the Style, Color tab. If it asks you to Share Style then click Yes.
• Then you can choose the colour of the buffer polygon. Reduce the Opacity to see the Google Earth imagery behind the polygon.
• It should now look like the image on the left. I can then reload my original polygon to show both (right):
• You’ll notice that on the website there are a number of other options too. Area calculates area (for polygons only), similar to GEPath. Generalize can smooth the outline of your line or polygon. The Cruise tool is described below.
Generating random points (Cruise tool)
If you are planning your sampling design for your fieldwork there are tools available that can create random or grid points. This tool uses the same website as previously. It creates random points in a way that you specify. We can then display them on Google Earth, or use another tool to convert those points to a format suitable to upload to your handheld GPS unit.
• Click on Add Polygon to create a polygon.
• On the Places sidebar right-click your polygon and choose Save Place As…
• Enter a filename and location to save, and save as .kml.
• Now go to http://extension.unh.edu/kmlTools/index.cfm
• Click Choose File to upload your saved .kml file.
• Enter a description and press Submit.
• Under the Cruise function, enter how many points you want to create. You can have them generated as a Grid (equally spaced throughout your polygon) or Random (randomly spaced throughout your polygon, with a minimum spacing that you specify).
• Click on the Cruise button. A new screen will pop up with your points. Save as .kml as before.
• Import the new file with your random points into Google Earth, it should now appear in the Places sidebar.
• On the Places sidebar right-click your polygon and choose Save Place As…
• Enter a filename and location to save, and save as .kml.
Google Earth doesn’t let you export these points to your GPS unit, so we need to convert the file. There are many different tools we can use to do this.
Converting your .kml file - Option 1
• Go to http://kml2gpx.com/. This website takes a .kml file from Google Earth and converts it to a .gpx (a common file format that your GPS unit can read).
• Under Convert file click on Choose File and upload your random point file.
• Press Convert. You can then download your new .gpx file or display the points on Google Maps if you want to verify them.
Converting your .kml file - Option 2 (you can skip this if you did Option 1)
• Download GPS Utility from www.gpsu.co.uk.
Note: This tool is not available for mac.
• Go FileàOpen and load your .kml. The file should open in the main window.
• Go FileàSave/Export Options.
• Click Export As… Make sure .gpx is selected.
• GPS Utility is useful for all sorts of other tasks e.g. converting to other file formats, changing coordinate systems, uploading different files e.g. shapefiles from ArcGIS, uploading to your GPS unit etc.
Uploading to your GPS
• Now you have your .gpx file you need to use the software that came with your GPS to upload the points onto your GPS unit.
• If you don’t have the software that came with your GPS unit, free software is available. You can try GPS Utility www.gpsu.co.uk, Garmin BaseCamp www.garmin.com/en-US/shop/downloads/basecamp or DNR Garmin www.dnr.state.mn.us/mis/gis/tools/arcview/extensions/DNRGarmin/DNRGar min.html
Terrain and elevation
Google Earth uses terrain data from the two main sources: the Shuttle Radar Topography Mission (http://www2.jpl.nasa.gov/srtm/) and the ASTER satellite (http://asterweb.jpl.nasa.gov/). This is relatively coarse data (e.g. 3 to 25 m vertical resolution. In some areas (e.g. the US) higher resolution data is available. To use higher resolution data (if available), go to Google Earth à Preferences and tick use high quality terrain.
Note: Mangroves are very shallow sloping, so the data may sometimes be too coarse for our work. However, it may be useful in some instances.
Also note: the elevation may not always refer to the ground. Sometimes it may include the tops of trees or buildings.
Viewing the terrain
• See topography on Google Earth by using the navigation arrows to tilt view.
• To increase the vertical exaggeration to better view the terrain, on the main toolbar go to Google Earthàpreferencesàvertical exaggeration (0.01-3). This makes hills etc seem taller.
Extracting elevation profiles
We can use the elevation data within Google Earth to show changes in elevation along a distance.
• Click on Add path. Draw a line on Google Earth where you would like to extract the elevation profile. This line can be multi-point (e.g. it doesn’t have to be a straight line).
• Click OK to save this path. It should now appear in your Places sidebar.
• Right-click on your new path file in the Places sidebar and select Show Elevation Profile.
• The Elevation Profile shows a number of things, such as min, max and average elevation, elevation range, min, max and average slope etc. You can also just isolate a section of your profile.
• Currently, there is not a way to save this elevation profile in Google Earth. But try saving the path as a .kml and exporting to a program such as GPS Utility.
Using historical imagery to show change through time
One of the most useful features of Google Earth is its huge archive of remote sensing data. New imagery is constantly uploaded to Google Earth, so we are able to use this archive to show change through time. For example, see the Figure below, which shows mangrove erosion between 2003 and 2010 for a mangrove in Singapore. The polygons were extracted from Google Earth, and then I highlighted the areas where erosion or vegetation expansion had occurred.
In some locations, Google Earth has even uploaded historical aerial photographs and maps from the early 1900s.
Areas in red are mangrove lost due to erosion between 2003 and 2010.
This Figure is taken from: Friess et al.
2012, Raffles Bulletin of Zoology S25, 55-‐65.
• Select the Historical Imagery button.
• A timeline slider will appear. Scroll to view imagery from different dates.
• You can then draw paths and polygons for each date to show change through time. You could then use GEPath to quantify the area, or convert the paths/polygons to shapefiles and import into other GIS software packages for further analysis.
Adding Google Earth imagery to ArcGIS
Sometimes you need to conduct advanced analysis on commercial GIS software. In this case it would be useful to import Google Earth imagery into GIS. The following information is taken from http://gis.yohman.com/up206a/how-tos/how-to-add-a- google-earth-satellite-image-into-arcmap/.
Note: everyone is a little unsure about the copyright issues surrounding the use and reproduction of Google Earth imagery.
In this guide, you will navigate to the location in Google Earth that you want to bring in to ArcMap. Then, you will add 4 control points on each corner of the image, record their latitude/longitude coordinates, and export the image as a jpg file.
1. Open Google Earth
2. In the Layers panel, turn everything off
3. Go to Tools -> Options, and change the “Show Lat/Long” option to “Decimal Degrees”
4. Navigate to the area and extent that you want to use in ArcMap
5. Press “r” on your keyboard. This will reset the view angle to be “top down”
and rotates the map so that it is “north up”
6. Press F11 to make your map go full screen 7. Click on the “add placemark” button
8. Move the icon from the middle of the screen to the top left corner of the map 9. Rename the icon “Top-left”
10. Click the button to change the icon
11. Choose this icon:
12. Jot down (or copy and paste) the latitude and longitude coordinates somewhere you can access later
13. Repeat the process and add icons for “Top-right”, “Bottom-left” and “Bottom- right”
14. Now it’s time to export the image. Go to File -> Save -> Save Image and save your file
ArcMap
Now you will import your google earth image, and georeference it based on the 4 control points you created.
1. Open ArcMap
2. Go to View -> Data Frame Properties and select the Coordinate System tab
3. Choose Predefined -> Geographic Coordinate Systems -> World -> WGS 1984 4. Go to Customize -> Toolbars -> Georeferencing
5. Add the image file from Google to ArcMap. If it prompts you to build pyramids, click ok
6. Zoom into the top left corner of your satellite image
7. From the georeferencing toolbar, click the “add control points” button
8. Hover over the exact center of the top left icon you created, and LEFT click once
9. Now, RIGHT click once and click on “Input X and Y…”
10. Add the correct coordinates for your Top-left control point.
WARNING: Remember that “X” is LONGITUDE and “Y” is LATITUDE 11. Repeat the process for the remaining 3 control points. If the map has
disappeared from your view port, just right click on the layer, and select “zoom to layer”
12. To finish your georeferencing, click on the “Georeferencing” menu item from the toolbar, and select “update georeferencing”
Google Earth Pro
Google Earth Pro costs US$399, and has a number of features not available on the freely downloadable Google Earth. You can download a free 7-day trial of Google Earth Pro.
- Measure areas, perimeters etc.
- Overlay your own images (e.g. aerial photos, maps) and other GIS data onto Google Earth Pro.
- Very high-resolution printing
A list of general (free) GIS resources
• Introduction to GIS, tutorials etc - http://gis.yohman.com/up206a/home
• Online GIS -‐ www.gpsvisualizer.com
• Interesting Google Earth tips - www.gearthhacks.com
• Free GIS layers – www.diva-gis.org/Data
Friess et al. 2011. Frontiers in Ecology and the Environment 9, 542.
