The open source GIS MapWindow (Windows only) has just put out its latest Stable Release (SR), version 4.5. This is the first SR in about 8 months. New features include:
Archive for the 'MapWindow' Category
This post has gotten a very strong reaction from many people, mostly negative. They say use of Google Earth imagery in the manner outlined here is inappropriate, an illegal violation of the Google Earth EULA/TOS. More specifically, words like “theft”, “stealing” and “dirty” have been used to describe this. I feel that this use of Google Earth imagery for personal and non-commercial uses falls under the guidelines of “fair use”, and I explain why here. “Fair use” is not theft. But I acknowledge that I could very well be wrong about this falling under the umbrella of “fair use” protection, in which case it would be illegal. I’d welcome opinions from those knowledgeable about the rights and limitations of “fair use”, and will pull the post if an expert on these issues says that using Google Earth imagery as described below doesn’t constitute “fair use”.
You can save the displayed view in Google Earth by using the File=> Save => Save Image command (Ctrl-Alt-S is the shortcut), which saves the contents of the view window as a JPG file. But in order to use this image in a GIS program, it has to be georeferenced, i.e. coordinates assigned to the pixels. There are free image georeferencing options out there, and I’ll cover some of those soon, but that’s not necessary in this case - there’s a simpler way to get the georeferencing data for an image exported from Google Earth.
You will need to have installed Google Earth (of course), the free GIS program MapWindow, and the Shape2Earth plugin for MapWindow. Shape2Earth’s main function is converting shapefiles to Google Earth KML files, and while the full version costs $29.95, it will work in unregistered demo mode for up to 500 shapefile vertices, and here for georeferencing Google Earth imagery.
1. Open Google Earth, and zoom in to the area of interest.
2. Double-click on the “N” in the compass at the upper right to orient north to the top of the screen. Also double-click on the “0 tilt” icon (the box with the “X” in it on the left in the tilt adjustor) to set the tilt angle to zero.
3. Open MapWindow; if you haven’t already activated the Shape2Earth plugin, do so from the plugins menu.
4. From the Shape2Earth menu in MapWindow, select “Get Image from GE”, and click on the “Capture Image” button. If you haven’t already oriented the image with north at the top and zero tilt, you will be prompted to do so.
5. Save the image with the desired name as a JPG file. This will save a black-and-white jpg image of the current view in the Google Earth window, along with a worldfile (*.jpgw) containing the georeferencing information.
6. Go back to Google Earth, and without moving or changing the view in any way, save the current view (File => Save => Save Image) with the same name and location as the image in step 5,. This overwrites the previous black-and-white image with a color one of exactly the same area.
You now have the Google Earth image with the georeferencing data contained in the worldfile (geographic coordinates, WGS84 datum), which most GIS programs can open and read successfully. If there’s a problem, try changing the extension of the worldfile from *.jpgw to *.jgw.
Limitations of this approach:
- The view in Google Earth is orthographic, i.e. you’re looking at a sphere from above. For views that are zoomed to view a relatively small area, the area is essentially a flat plane, and the georeferenced image shouldn’t have a large deviation from the true coordinates. The larger the area covered, the greater the deviation between the true and georeferenced coordinates.
- Coordinates in Google Earth can be off from the true coordinates even for small areas; see this post for more info. This process doesn’t correct for any such deviation.
- Imagery in Google Earth is copyrighted, and using it for any other purpose than viewing in Google Earth falls under the restrictions of copyright law and fair use. In particular, you have to leave the Google logo and copyright notices unaltered to maintain proper attribution.
Two GIS programs I’ve posted about have recently released updated versions:
MapWindow: An updated version of Stable Release 4.4 is available. The only change I could spot is PostGIS import/export, but typically these updates include bug fixes as well.
SAGA: Updated to version 2.0.1. No huge changes, primarily fixes to the Linux GUI, a new tab that shows map thumbnails, and a few new modules.
Just a brief note to say that the open source GIS MapWindow has reached version 4.4, and the new version is definitely a worthwhile upgrade if you already have the program. A whole bunch of shapefile editing capabilities have been added, there’s now an Undo function in the shapefile editor you can turn on, higher-resolution raster export, plus bug fixes and a few other features. I plan to do a video in the near future demonstrating these new capabilities, similar to the ones I’ve done before on MapWindow.
Last week, I posted on how to create an animated depiction of sea level rise due to a storm surge or global warming. Here’s a movie of the flooding for the Manhattan/NYC area:
JS writes, “I am doing a very small wireless operation in Catalonia, and it would be very interesting to have the coverage map of the antennas. Do you know any free (or cheap) tools to do that and place it on Google Earth?” I know of two free Windows tools useful in analyzing radio coverage. The first one is a general purpose terrain analysis program that will give “quick and dirty” plots of line-of-sight coverage and required antenna heights fairly easily. The second, more sophisticated program is specifically designed for determining broadcast coverage and signal strengths, but is also more difficult to use. Getting the data products into Google Earth can take some work, but can be done.
Continue reading ‘Mapping Radio Coverage, And Viewing It In Google Earth’
In a previous post, MicroDEM was used to create viewsheds from a DEM (digital elevation model), and plot them on top of either a DEM terrain image or a corresponding map loaded into the program. But it could be useful to export the viewshed data alone, either in raster or shapefile vector format, for use in other GIS programs. More generally, the need might arise to convert a general raster image of an area into a polygon shapefile. You can do this with the Spatial Analyst extension for ArcGIS, but the two together are pretty expensive. There’s a somewhat painless way to do it with free software.
Continue reading ‘Converting Raster Area Images Into Polygon Shapefiles’
There are a number of free ways to convert shapefiles to KML format for display in Google Earth, but fewer and less flexible shapefile display options for Google Maps. This site lets you upload small line and polygon shapefiles for display in Google Maps, but not in a permanent form, and with limited display options. This other site details a procedure to display polygon shapefiles in Google Maps, but it’s not particularly straightforward to implement. There’s also some direct support for displaying simple KML files in Google Maps, so you could always try converting the shapefiles to KML and then opening them in Google Maps. But there’s a Java application that makes the process reasonably straightforward for polygon shapefiles, shows the data already loaded in a Google Maps interface, and offers some added display options.
Continue reading ‘Thematic Polygon Shapefile Display In Google Maps’
