World Wind

In the past, in order to create realistic Landsat/DEM overlays for example it was necessary to understand and access a DEM dataset such as the SRTM or USGS SDTS dataset. If using SRTM, you had to deal with null data areas. It was also necessary to understand the Landsat dataset, be able to identify and download the appropriate bands, and then to possess the skill and art to create "true color" RGB images from the individual bands. Cloud cover was aways an issue. Finally, it was necessary to possess the software and the skill to create and view 3D terrain overlays by combining the DEM data and the Landsat image using an appropriate software package. If you desired USGS topo maps, you had to access on of the USA state GIS archives and hope that your target state offered free maps.

Thanks to World Wind, this is no longer necessary, as this program will do all of that and more using flawless images from a single archive. In addition, these terrains and maps can be constructed effortlessly using a "point and click" mouse interface. In short, the authors of this software have attempted to present these and other datasets to the masses. Despite some notable shortcomings, they have largely succeeded.

World Wind is a Microsoft .NET-based "smart client" application, meaning that the program uses the local machine for processing power and to archive some data and uses the network (the Internet in this case) to access other data (which is archived on a NASA server).
A couple of notable points about World Wind. First of all, the application is huge: 540MB. It also requires that you download the Microsoft .NET application environment. You will find a broad band ISP connection very helpful in downloading and using this program. This application will definitely stretch your system resources to the absolute limit.

The program fully taps the unique and rich USGS and NASA datasets that we enjoy in the United States. The interface is still useful for the rest of the world, but those users who are interested in locations within the United States will gain more benefit from the program.

On the negative side, the program is a slow, ugly, greedy resource pig. It will absorb all of your system resources while it is operating, and may continue to bog down your system even after you exit. Only a reboot seemed to fully reset my system after World Wind got through with it. While it is operating, it does not require, nor does it ask for explicit permission to accesses the World Wind server. Forget about running other applications either on the Internet or on the local machine while World Wind is live (especially if you use a dial-up connection), as your system will be hard pressed to accommodate the application when running clean. The USGS topo download feature seems to run forever, regardless of the current LOD. The seemingly endless download loop monopolizes bandwidth whenever the topo feature is active. Some of the many bugs are surprising to say the least. For example, the image save feature (called Screenshot in World Wind) failed to function on my computer. It is hard to understand how professional developers can release an application lacking something as basic as image save capability. (All of the images on this page were captured with MWSnap, which World Wind barely tolerated.)

Program Features
When you open the application, you will be presented with a 3D view of the planet earth. This interactive image was generated with the Blue Marble data set, according to the World Wind website. It is a striking image albeit with comparatively low spatial resolution. You can use your left mouse button to spin the globe and the mouse wheel to zoom in (to an extent practically limited by the inherent resolution of the image) to any place on the globe. At the top of the view port you will find a set of toolbars, a conventional Microsoft system toolbar and a more cryptic application toolbar with a series of icons. (more on the latter set later).

While it is tempting to just spin around the globe until you find the place you think that you are interested in and then use the mouse thumbwheel to zoom in, take my word that this is not a great idea. The problem is that many places look alike from 500,000m elevation and it is very expensive (computationally) to zoom in and out of a location if any of the World Wind functionality is set. This is because World Wind uses a MRSID-type approach to data access. It starts off by presenting the user with a low-resolution image set and then successively loads higher resolution tiles based on the current level of zoom. Since the program loads its data from a remote location, needless zooming in and out can in general waste quite a bit of time and bandwidth. Note: when World Wind is loading data, you will see a red rectangle on your screen and a NASA icon in the lower left corner of the view port. There will be a small progress bar that will indicate the status of the download of the data in that particular rectangle(usually).

A better alternative is to use the World Wind 'Place Finder'. This very handy tool in the 'View' menu allows you to specify the center of the image based either on inputting latitude and longitude coordinates or by picking the name of the location from its automatic search engine. To discuss the optimal procedure better, I must introduce the World Wind toolbar. At the top of the view port you will find a series of icons with tool tip popups. Activating one of these icons will instruct the application to access the remote server to pull up the specified image information. USA users will find the "NLT Landsat Visible Color" and 'USGS Topo Maps" icons especially useful. In order to save yourself time and to minimize the load on the NASA server IT IS IMPORTANT THAT YOU FOLLOW THESE INSTRUCTIONS:

2) SET VERTICAL EXAGGERATION TO ZERO. (Vertical exaggeration is set in the 'View' menu.)
3) Zoom in to your area of interest using whichever technique suits you (see above comments.) Zoom in to the approximate final level of zoom that you will desire EVEN IF THE IMAGE IS EXTREMELY BLURRY DUE TO LOW RESOLUTION.
4) Set the approximate viewing angle using the RIGHT MOUSE BUTTON. When you depress the right button, you will be able to tilt and rotate the view as desired. (This feature is not very clear in the sparse user documentation for the application.) Basically, moving the mouse horizontally with the right button depressed tilts the image, while moving it horizontally spins the image in a somewhat confusing and to me counter-intuitive way.
5) Now switch on the dataset icon that you are interested in. If you choose the Landsat option for example, you will see the NASA icon at the lower right corner indicating that World Wind is loading the dataset required for your field of view. (Note: oblique perspectives will require a much longer period of time to load data. World Wind in the (understated) words of the developers "is not optimized for speed". As a result, it will load every tile in the field of view to the same level of detail (LOD), meaning that the itsy-bitsy tiles 'way off in the distance will take just as much time to download as those large ones in the foreground.) In the future perhaps the developers will realize that a distant tile that takes up 150 pixels does not benefit as much from high resolution as a large tile in the foreground and tune the program accordingly.)

If this procedure is followed, even users of dial-up modems can get an almost bearable level or performance. If multiple functionality is switched on during the zoom, World Wind will load many partial tiles worth of unnecessary data during the course of zeroing in on the area of interest. If you fully zoom first, and then switch on the icons, World Wind will only attempt to load a few tiles worth of high resolution data. (Note: once you search your location, it is a good idea to save the exact coordinates of your target. World Wind 1.3 has an annoying habit of irretrievably losing its icon toolbar during the course of use. There are hot keys that you can use in this case or alternatively you must reload the program to retrieve the icons.

A World Wind issue that you will certainly experience is the bizarre screen artifacts that will plague your efforts to position the final viewing perspective when you are working at essentially maximum zoom. These seem to be some type of clipping plane intrusions characteristic of the Direct X 3D modeling image. Hopefully the developers will mitigate this problem in future releases as this is without doubt the worst technical deficiency of the program. In the meantime, prepare yourself for some truly dazzling screen jitter that will consume the entire screen just as you are making that final adjustment to your target image. I have not found a way to avoid this problem that seems to be especially associated with high zoom oblique perspectives. In order to produce the images shown on this page I had to adjust the zoom, tilt, pan and rotate until I found a "sweet spot" that was free or relatively free of obstruction. The problem can actually be worse with vertical exaggeration set to zero, so set it to a non-zero multiple before attempting final adjustments. A sample of what I am talking about can be seen in the image to the right.

The general technique described above was used to produce the two sets of images shown to the right. The first is a USA location in Death Valley National Park, USA, showing the area of Badwater and Shorty's Well. The second is a non-USA location of a remote valley in the Hindu Kush in northern India. For USA locations, you may wish to examine the USGS topographical map corresponding to your terrain. This can be conveniently done by activating the appropriate icon at the top of the screen. The USGS topo maps are also loaded in successive levels of detail. The first image to the right is a relatively low-resolution rendering while the second image shows a higher resolution map that resulted from closer zooming.

I was initially confused regarding World Wind's use of SRTM DEM terrain data as there is no SRTM icon. In World Wind, the SRTM database is accessed whenever the vertical exaggeration that is set in the 'View' menu is non-zero. As mentioned previously, having SRTM data active while browsing overhead views is a needless waste of bandwidth and will slow things down considerably. However, the stunning integration of Landsat and SRTM data will be very obvious when you have both of these functions active and then when you pan to a perspective view. In fact this combination is the most powerful and impressive for the entire application. World Wind performs real time Land sat drapes over SRTM data that produces truly stunning terrain perspectives. Samples of some of this awesome technology can be seen in the series of perspective images to the right.

Finally, you may look at a 1m ortho image of your target location (if it is available) by selecting this option from the toolbar. This will give you the highest resolution of any of the World Wind data sets. However, this data is not available for all regions in the USA and not available at all outside of the United States.

While I have used a USA location for this example, the program is almost as good for non-USA locations. The main difference is that the underlying SRTM dataset is 90m resolution instead of the higher 30m resolution available in the States. USGS topographic maps are of course not available either.

Some discussion of the sources for one of the key datasets used is worth mentioning as well. Previously, the only source for global Landsat data was the GLCF database hosted by the University of Maryland, which I described in an article posted in 2002. Since that time, Land sat data has become available from the Jet Propulsion Laboratory's JPL's OnEarth website. The main advantages of the JPL and World Wind interfaces is that they present "true" color renderings constructed by combing three Land sat bands using appropriate image processing algorithms. This saves the user the considerable effort of manual rendering as described elsewhere on this page.

Documentation for World Wind is sparse. There is no user manual and the website is does not offer much in the way of instruction either. Dan Sanders wrote an excellent manual entitled Introduction to World Wind, which you will find most helpful indeed.

In summary, World Wind, despite its numerous and exasperating shortcomings, represents the finest terrain viewing application ever to be presented to the public. It also represents a huge step forward for NASA. Although the funding for this effort probably represents one millionth of the total NASA budget, it is an initiative that provides a clear, direct and tangible benefit to hundreds of thousands of users world wide, which unfortunately cannot be said for many agency inititives (read: "International" Space Station).


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