Example: Import DDF SDTS DEM Raster File

In this example we import a DDF, SDTS file containing raster data showing terrain elevation data in the Livermore, California, valley.  We use Style to provide a more understandable display by applying hill shading and a palette.  See also the companion Example: Import DDF SDTS DLG Vector File topic.


A sample project containing this data set, formatted as seen in this topic, may be downloaded from the Downloads page on the Manifold web site.


Spatial Data Transfer Standard (SDTS) format was popular for many years as the primary GIS data interchange standard for the U.S. federal government. Most USGS vector drawings (DLGs) and raster images/surfaces (DEMs) were converted into and published using SDTS format. In both cases the three-letter DDF extension is used for file names that contain SDTS data.  

SDTS DDF Raster Files

SDTS format normally includes a large number of files organized within a folder One of the files often will be a catalog file that ends in "…CATD.DDF".   For example, in the illustration below of a folder for terrain elevation data for the Alameda quad  published by USGS in their 1:24K series there are 19 files.



One of the files (highlighted) is named 1475CATD.DDF.  That is the catalog file.   To import an SDTS data set, browse to the directory that contains the files and import the ...CATD.DDF file. Manifold will read the catalog and automatically organize the import of all files involved.  If there is no file that ends in ...CATD.DDF  then usually a good strategy is to choose the largest file in the folder.



To import from DDF, SDTS format:


  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the folder containing data of interest.

  3. Double-click the file ending in ...CATD.DDF

  4. Tables and drawings and comments will be created.



Clicking on the 1475CATD.DDF file for the file folder shown above will result in the creation of a collection of tables, an image that uses one of the tables and comments.



For a more interesting display, we first create a map using a Bing streets image server as a base layer and using the 1475 ELEVATION Raster image as a layer. We then double-click the map to view it.   



The image appears in the correct location, because SDTS format provides projection information for the data, but it clearly could use some styling to be more understandable.   To apply styling, with the focus on the 1475 ELEVATION Raster image layer tab we use the Style pane.



In the Style pane we leave the default choice of equal intervals in the Method box.   For Fill we use the closest lower value choice.  We use the default number of 5 in the Breaks box and then we press Tally to load the palette pane with five ranges of values.  We click the Apply palette button and choose the Altitude palette from the Classic palettes submenu.  Press Update Style.  



The result is a flat, contour-like presentation as pixels within the given range of heights are colored the same color.  To make a more interesting display we shall turn on shading.


We click the Options tab.



We check the Use shading box and then we enter 0.3 into the Z scale box.  We could have started with the default Z scale value of 1 and then tinkered with the value to achieve the effect we want, but from experience we know that a Z scale value of about 0.3 seems to provide a more pleasant effect with USGS DEM data.    We press Update Style to apply shading.



Well, that is certainly much better!   Sometimes it is amazing what a difference one small option can make.



We can confirm the data set has been imported with the correct projection by adding a terrain layer, the Migurski's Terrain presentation of OpenStreetMap terrain,  behind the image and a Google streets layer with transparent background above the image layer.  These show that the hill shaded terrain elevation presentation created by Manifold matches very closely to the OSM-computed terrain.


We can see that this portion of the Alameda data provided by USGS includes the location of one of the two US government nuclear weapons design centers, the Lawrence Livermore National Laboratory.  The other center is in New Mexico, at Los Alamos.


The image seen above is the same map published in larger size and also in a false color version on the Data Sources page on the Manifold website.  


See Also

Style: Images


Style: Invisible Pixels


Style: Contouring using Colors




Example: Spectacular Images and Data from Web Servers


Example: An Imageserver Tutorial


Example: Import DDF SDTS DLG Vector File