Yesterday’s post dealt with Trimble’s Planning Software, which lets you calculate a GPS-satellite-geometry-dependent error parameter called “Dilution Of Precision”, DOP for short. The calculated DOP can tell you when the GPS satellite geometry is favorable (or unfavorable) for reducing errors due to GPS satellite geometry. But those calculations assumed that you had an unobstructed view of the entire sky, and had line-of-sight to every GPS satellite above the horizon. In many cases, though, your view of GPS satellites is likely to be obscured, either by local obstacles like buildings and vegetation or more distant ones like topography. There’s not much you can do about taking the former into account, but there is a way to deal with the latter to some degree.
Continue reading ‘Determining Terrain Effects On GPS Accuracy’
Previous posts have shown how to display parameters such as elevation, slope, and aspect in MicroDEM on a “global basis”, plotting these parameters individually across an entire DEM. But it’s also be useful to show which areas on a DEM fit within a specific range of values for these parameters, e.g. what areas have a slope greater than 50% but less than 100%. MicroDEM can do this kind of terrain categorization.
Continue reading ‘Selecting Areas Based On Terrain Categories And Values: Slope, Elevation, Aspect And Relief’
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’
