NASA’s Goddard Space Flight Center in Maryland maintains the Global Change Master Directory, one of the largest (if not *the* largest) collections of links to data I’ve found on the Internet, somewhere on the order of 15,000. While the header refers to “Earth science data and services”, it’s not limiting itself to the traditional definition of “Earth science” there (i.e. fields like geology, geophysics, meteorology, etc.).
The data is initially divided into 14 broad groupings:
Going to these pages, you’ll find the topics broken down further into subtopics, and even sub-sub-topics. For example, under Climate Indicators, you’ll find sub-topics for:
You can also search for data by map, date or location name. This is a “must-bookmark” data resource.
In addition to displaying elevation directly, either as terrain or colors, MicroDEM can also display elevation derivatives. Examples include curvature, relief, summits and ridges, but the simplest are probably slope and aspect.
Continue reading ‘Terrain Slope/Aspect Display And Analysis’
In earlier posts on MicroDEM, the digital elevation model (DEM) has been displayed in reflectance mode, terrain illuminated by light coming from an angle. But it’s also possible to display the elevations as different colors for use as a background image for maps, or for shading.
Continue reading ‘Elevation And Contour Line Display In MicroDEM – Make Your Own Simple Topo Maps’
Animated viewsheds – how cool is that?! In an earlier post, I covered how to create basic line-of-sight and viewshed plots in MicroDEM i.e. what you can see from a specific point. But MicroDEM also has some advanced viewshed features that allow you to determine what fraction of a defined area is visible from a specific point, and also the visible terrain not just from a single point but along a route. And the route observations can be converted into an animated representation of the visible terrain from every spot on the route.
Continue reading ‘Advanced And Animated Viewsheds With MicroDEM’
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’
Although you view a DEM (digital elevation model) as a two-dimensional representation of terrain in MicroDEM, the program can treat it as a 3-dimensional surface and analyze it as such. Perhaps the simplest example of this is in answering the question, “What terrain can you see when you’re standing at a specific location?”, and MicroDEM has tools that let you do that.
Continue reading ‘"I Can See My House From Here": Line-Of-Sight And Viewsheds In MicroDEM’
Yesterday’s post dealt with the basics of installing MicroDEM, and opening up DEM terrain files in the program. Now it’s time to look at different ways to display terrain reflectance in DEM. While 3DEM is better for some kinds of displays, MicroDEM has more different ways to display reflectance.
Continue reading ‘Modifying The Terrain Reflectance Display In MicroDEM’
As you might guess from the name, MicroDEM is a program that works with digital elevation models (DEMs), plots of elevation as a function of position, the same kind of data used by 3DEM. But MicroDEM contains far more features and capabilities than 3DEM, and includes other non-DEM related features as well. I like to think of MicroDEM as a “Swiss army knife”, since it contains so many interesting and useful tools. Even if you’re not into GIS, MicroDEM is worth looking at for its terrain visualization and analysis capabilities. I could post for month or two on just MicroDEM alone, and by the time I’m done, the posts will likely add up to at least a month’s worth. But to start, I will do a number of posts over the next week or so on just a little of what MicroDEM can do. Bear with me on the first few – I have to get through some of the basics of program installation and operation before I can get to the really cool stuff.
Continue reading ‘MicroDEM: A Swiss Army Knife Of Terrain And GIS Tools’
