Tuesday, January 6, 2009

Image Data - for Pro's and Newbies



Pro's
If you are looking for some nice satellite images, the USGS Global Visualization Viewer is the tool for you. Once you scroll to the image you need, right click and choose "add to list". On the bottom left hand side, click the Download button to retrieve the image. Note that most images are downloadable but some are not. Tweak the date in the of the image to find a downloadable file.
You
can also choose the collection of images on the top "Collection" menu. The Landsat Archive - "L7SLC off (2003+)" are your best choice for up to date images. However, they have some annoying lines running through them, but still they are useful for a lot of scientific work. If you just need a nice backdrop image choose Landsat Decadal and "ETM+ Pan (1999-2003)". All images have a resolution of 30m or 15m (per pixel) if pan sharpened. For a groovy display of recent or temporal data use the L7SLC images and digitize interesting features as Shapefiles, then display them on the older ETM+Pan backdrop image.

If you are working in a country with a bad internet connection make sure you install a download manager before you start the download. This will help as it resumes downloads even if the connection has been interrupted or the computer has been shutdown.
The images are zipped and around 250mb. Unzipped, they will be around 1GB. Since you will get all image bands, use the open source software OS
SIM for stacking and pan sharpening your images. Here is the link to the PDF Tutorial for the easy to use and stable software.

To unzip the images you will need to use IZArc as Winzip will not do the trick.

If this stuff bores you and you want to explore other remote sensing data options such as radar etc. use NASA's EOS Data Gateway.

Newbie
If you are a GIS newbie and don't k
now about bands and all that fun stuff, you can download pretty good images (250m resolution) from the True Marble website.

A good alternative is also to embed Google Earth images into your GIS software. Download MapWindow GIS (easy to use and stable open source GIS application) along with the Google Earth plugin. After installation, open Google Earth and navigate to the image extent you need. In the MWG Plugin Menu, select Shape2Earth. The Shape2Earth menu will appear. Here, click on "Get image from GE" and save the image to your computer. It will be georeferenced. If you need the image in color use these instructions.


If the term GIS scares you and you just want to look at an image, use Google Maps or Google Earth. Or try FlashEarth which will also show you images of other digital globe applications.

For all users with a bad internet connection try saving the Google Earth images to your hard drive by caching them. This means you can view the images using Google Earth even though you are not online. It is quite easy to do. when you have internet connection, open GE and zoom to the image you would like to save. That's it! Now go offline and you will see that this image is saved when you open Google Earth and navigate back to the previous extent.

18 comments:

Brentles said...

Oooo, I actually just tried that flashearth site, pretty cool!

The zoom level sucks though for Penang, can't even see my house :-(

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