Tag Archives: DEM
by Stephen Jackson, Graduate Research Assistant, Center for Research in Water Resources, The University of Texas at Austin, email@example.com Extracting hydrologic features such as stream centerlines and watershed extents from a Digital Elevation Model (DEM) typically requires first hydrologically conditioning … Continue reading
Contours are lines that connect locations of equal value in a raster dataset. They are useful because they can show the shape of the phenomena represented by the raster surface that may be otherwise difficult to see. In addition to … Continue reading
The TopoToRaster tool is primarily used to create hydrologically correct digital elevation models (DEMs) from contour data. Additional input information such as spot heights, known locations of sinks, streams and the outline of lakes can also be used to further … Continue reading
Imagery Analysts frequently have to measure features and determine their height. At ArcGIS 10.1, the Image Analysis window provides tools that give you the ability to take measurements of building heights directly from imagery. The process of making such measurements on imagery is referred to as mensuration. Mensuration tools apply geometric rules to find the length of lines, surface areas, or volumes using information obtained from lines and angles. Mensuration can include measuring the height and absolute location of features. Any georeferenced raster dataset can provide distance, area, point, and centroid location. Height measurements can be obtained when the sensor model is known. Sun angle information is required for measurements using shadows, while 3D measurements require a DEM.
This image shows how you could use the Base to Shadow tool to find the height of a building. The height is calculated by selecting a point at the base of the building and the corresponding point at the top of the shadow. For more information on the Mensuration tools and how to use them, see the ArcGIS Online Help.
Contributed by Natalie Campos.
Elevation data is an essential piece of GIS data for hydrologic applications, but it’s big, not always easy to get and for modeling surface water flow requires specialized processing to become useful. Elevation data and services are coming to ArcGIS Online, including some hydro specific capabilities.
World Elevation Services
The World Elevation Services became available for beta testing last fall and will be released at the end of March. There are image services, data download services, and analysis task services available, as well as sample applications. The services are built from a collection of data sources, ranging from less than a meter resolution up to almost 5 kilometers, and includes services of elevation, shaded relief, slope, and aspect. We will continue to add new data as it becomes available. Like other things on ArcGIS Online these services can be used in Desktop and any other Esri clients, and also in other applications via REST or SOAP. http://resources.arcgis.com/content/imagery/10.0/world_elevation
Since you’re reading the Hydro Blog, your obvious thought is, when can I start using elevation web services for water resources applications? You’ll be happy to know we’re working on it. You’ve probably noticed a shift happening in ArcGIS Online and the Resource Centers to more specific application areas, in places like ArcGIS for Local Government and right here for Hydro.
By Dr. A Jon Kimerling, Professor Emeritus, Oregon State University
If you’ve used any raster DEM data to make maps you may have at one time or another asked yourself, “What is the appropriate map scale for the DEM I am using to make the map?” This question is tied closely to a basic principle of map compilation that you may have learned in your beginning cartography course: “Always compile your map from source materials of the same or larger map scales”. In our age of digital elevation models and other raster datasets, this basic principle of map compilation can be restated as: “Always create your raster map from data at the same or higher spatial resolution than the ground resolution of your map display grid cells”. The ground resolution of your map display grid cells will depend on the scale of your map. An equation you can use that relates map scale expressed as a representative fraction (1/x), DEM cell resolution, and map display resolution is: