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.
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 from Smith and Sandwell, and DTED data.
demdataui looks for these geospatial data files on the
MATLAB® path and, for some operating systems, on CD-ROM disks.
When it opens,
demdataui scans your Mapping
Toolbox™ path for candidate data files. On PCs, it also checks the root
directories of CD-ROMs and other drives, including mapped network drives.
This can cause a delay before the GUI appears.
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.
data for areas currently visible on the map. Use the mouse to zoom
in or out to the area of interest. See
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 searches for data files on the MATLAB path. On some computers,
demdataui also checks
for data files on the root level of letter drives.
looks for the following data:
etopo5: The files
tbase: The file
satbath: The 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
/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.
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. The
demdataui function returns one or more matrices as an array
of display structures, having one element for each separate
get you requested (assuming you did not subsequently
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,
= demdata(1).map; refvec = demdata(1).maplegend. Use
create easy displays of the elevation data (for example,
meshm to add regular data grids to existing
surfm or a similar function for
geolocated data grids (for example,
The Close button closes the
Read from data sets that
located. You will not necessarily have all the DEM data sets shown in this
example. For information about finding data sets over the Internet, see Find Geospatial Raster Data.
demdataui UI. It scans the path for data
before it is displayed.
The Source list shows the data sets that were found. Here, the source is selected to present all DTED files available to a user.
Click GTOPO30. In this example, there are available GTOPO30 tiles. The coverage of each data set is indicated by a yellow tint on the map with gray borders around each tile of data.
Use the map in the UI to specify the location and density of data to extract. To interactively set a region of interest, click in the map to zoom by a factor of two centered on the cursor, or click and drag across the map to define a rectangular region. The size of the matrix of the area currently displayed is printed above the map. To reduce the amount of data, you can continue to zoom in, or you can raise the Samplefactor slider. A sample factor of 1 reads every point, 2 reads every other point, 3 reads every third point, etc. The matrix size is updated when you move the Samplefactor slider.
Here is the UI panel after selecting GTOPO30 data and zooming in on the Indian subcontinent.
To see the terrain you have windowed at the sample factor you specified,
click the Get button. This causes the GUI
map pane to repaint to display the terrain grid with the
demcmap colormap. In this example, the data grid
contains 580-by-568 data values, as shown below.
If you are not satisfied with the result, click the Clear button to remove all data previously read in via
Get and make new selections. You might
need to close and reopen
demdatui in order to select a
new region of interest.
When you are ready to import DEM data to the workspace or save it as a MAT-file, click the Save button.
demdataui does not recognize data you think it should
find, check your path and click Help to read about how
files are identified.
You can add the data grids to map axes using the
Updating the data returned by
demdataui to geographic
data structures (geostructs) using the
function is not supported because they are of type