One of the more common types of GIS data are terrain data, sometimes referred to as Digital Elevation Models (DEMs). These DEMs are raster datasets where each pixel represents a value of the earth’s elevation. The resulting digital representation of the earth’s surface is used by different types of terrain analysis, including hydrology and visibility analysis, and often used in cartographic rendering in GIS mapping.
Boundless Desktop includes many different tools for raster analysis including QGIS native algorithms as well as algorithms from GRASS GIS, SAGA GIS, GDAL and others. The benefit here is different tools may have different parameters, or support different input or output formats, so more choices ensures the user always has a tool to meet their needs. But this can also lead to some confusion, as novice users may not know which tool is best for a particular analysis. So to help clear up any confusion, we developed a Terrain Analysis plugin which consolidates several of the most common (and mature) terrain analysis tools in the single, easy to find place.
Boundless Desktop Tools For Raster Analysis
Once installed, the Terrain Analysis plugin adds a new toolbar to QGIS. The following commonly used terrain analysis tools for raster analysis are exposed directly on the toolbar:
Raster Analysis Tools:
- Hillshade – creates a cartographic model of shadowing across a terrain surface creating a 3D effect for visual relief
- Slope – an analysis which measures the incline or steepness of a surface
- Aspect – creates a result representing the compass direction each pixel in a terrain surface.
- Clip (by extent) – Cuts or extracts a subset from a larger raster (sort of like a cookie cutter).
- Profile – Creates a graph of the elevation of a surface along a line
- Viewshed – an analysis which denotes the locations visible from one or more specified observer points
The first four tools (Hillshade, Slope, Aspect and Clip) are quick access shortcuts for existing tools in the QGIS Processing Toolbox. Specifically, the Boundless team chose the GDAL algorithms from QGIS Processing toolbox because they are stable, feature rich and support a lot of raster formats natively.These will open the default processing dialogs for each tool as shown in the example below:
The Profile tool creates a terrain profile from a line drawn over a DEM. Just select a DEM layer in the QGIS layer tree, click on the tool button and draw a line across the map canvas. The resulting profile will be opened in the web browser.
The Plot.ly library, used for drawing the terrain profile, allows users to interact with profiles by zooming, panning, exploring values and exporting result into image. It is also possible to share generated profile with others by publishing it into Plot.ly server.
The Viewshed tool used to get visible/invisible areas around the observation point taking in account relief represented by a DEM. All you need is to select DEM layer in the QGIS layer tree, click on the tool button and select the observation point on the map canvas. The plugin will compute the viewshed and load it into QGIS. To make results easy to understand, a style applied by default shows visible areas in green and invisible in red.
Boundless will continue to increase the capabilities of the Terrain Toolbar in the future, as we attempt to make these types of analyses easier to perform in Boundless Desktop. In the meantime, please feel free to submit ideas to our Ideas Portal at ideas.boundlessgeo.com.