UI for selecting digital elevation data
demdataui is a graphical user interface to extract digital elevation map data from a number of external data files. You can extract data to MAT-files or the base workspace as regular data grids with referencing vectors.
The demdataui panel lets you read data from a variety of high-resolution digital elevation maps (DEMs). These DEMs range in resolution from about 10 kilometers to 100 meters or less. The data files are available over the Internet at no cost, or (in some cases) on CD-ROMs for varying fees. demdataui reads ETOPO5, TerrainBase, GTOPO30, GLOBE, satellite bathymetry, and DTED data. See the links under See Also for more information on these data sets. demdataui looks for these geospatial data files on the MATLAB® path and, for some operating systems, on CD-ROM disks.
You use the list to select the source of data and the map to select the region of interest. When you click the Get button, data is extracted and displayed on the map. Use the Save button to save the data in a MAT-file or to the base workspace for later display. The Close button closes the window.
The map controls the geographic extent of the data to be extracted. demdataui extracts data for areas currently visible on the map. Use the mouse to zoom in or out to the area of interest. See zoom for more on zooming.
Some data sources divide the world up into tiles. When extracting, data is concatenated across all visible tiles. The map shows the tiles in light yellow with light gray edges. When data resolution is high, extracting data for large area can take much time and memory. An approximate count of the number of points is shown above the map. Use the Samplefactor slider to reduce the amount of data.
The list controls the source of data to be extracted. Click a name to see the geographic coverage in light yellow. The sources list shows the data sources found when demdataui started.
demdataui searches for data files on the MATLAB path. On some computers, demdataui also checks for data files on the root level of letter drives. demdataui looks for the following data: etopo5: new_etopo5.bil or etopo5.northern.bat and etopo5.southern.bat files. tbase: tbase.bin file. satbath: topo_6.2.img file. gtopo30: a folder that contains subfolders with the data files. For example, demdataui would detect gtopo30 data if a folder on the path contained the folders E060S10 and E100S10, each of which holds the uncompressed data files. globedem: a folder that contains data files and in the subfolder /esri/hdr and the *.hdr header files. dted: a folder that has a subfolder named DTED. The contents of the DTED folder are more subfolders organized by longitude and, below that, the DTED data files for each latitude tile. See the help for functions with the data source names for more on the data attributes and internet locations.
The Sample Factor slider allows you to reduce the density of the data. A sample factor of 2 returns every second point. The current sample factor is shown on the slider.
The Get button reads the currently selected data and displays it on the map. Press the standard interrupt key combination for your platform to interrupt the process.
The Clear button removes any previously read data from the map.
The Save button saves the currently displayed data to a MAT-file or the base workspace. If you choose to save to a file, you will be prompted for a file name and location. If you choose to save to the base workspace, you can choose the variable name under which the data will be stored.
Use load and displaym to redisplay the data from a file on a map axes. To display the data in the base workspace, use displaym. To gain access to the data matrices, subscript into the structure (for example, datagrid = demdata(1).map; refvec = demdata(1).maplegend). Use worldmap to create easy displays of the elevation data (for example, worldmap(datagrid,refvec)). Use meshm to add regular data grids to existing displays, or surfm or a similar function for geolocated data grids (for example, meshm(datagrid,refvec) or surfm(latgrat,longrat,z)).
The Close button closes the demdataui panel.