U.S. Geological Survey Digital Elevation Model (USGS DEM) Reader Parameters

DEM files can be very large, and you may not always need all the data at the full resolution of the input DEM (if you are testing, for example). For this reason, you can enter a decimation factor that specifies how much of the file is skipped. If you enter a factor of 1, you will get the entire file. If you enter a factor of 2, you will get every second point horizontally, and every second point vertically (thus significantly reducing the file size).

DEM files can be interpreted by FME as a group of associated point features or as a single grid feature. These settings determine which way FME will handle the raster data. Raster files can be translated much more efficiently as grid features than as many point features.

If Read as DEM Grid is selected, each raster file is handled as a single grid feature.

If Read as DEM Grid is not selected, the elevation values in a raster file are handled as individual point features.

This parameter allows you to choose different naming schemes, and the number of feature types generated for the reader.

Feature type name choices:

• From File Name(s): Generates one feature type per source filename.
• From Format Name: Produces only a single feature type containing the format name.

Use this parameter to expose Format Attributes in Workbench when you create a workspace:

• In a dynamic scenario, it means these attributes can be passed to the output dataset at runtime.
• In a non-dynamic scenario where you have multiple feature types, it is convenient to expose additional attributes using this one parameter. For example, if you have ten feature types and want to expose the same attribute in each one, it is easier to define it once than it is to set each feature type individually in the workspace.

Using the minimum and maximum x and y parameters, define a bounding box that will be used to filter the input features. Only features that intersect with the bounding box are returned.

If all four coordinates of the search envelope are specified as 0, the search envelope will be disabled.

When selected, this parameter removes any portions of imported features being read that are outside the Search Envelope.

The example below illustrates the results of the Search Envelope when Clip to Search Envelope is not selected (set to No) and when it is selected (set to Yes).

• No: Any features that cross the search envelope boundary will be read, including the portion that lies outside of the boundary.
• Yes: Any features that cross the search envelope boundary will be clipped at the boundary, and only the portion that lies inside the boundary will be read. The underlying function for the Clip to Search Envelope function is an intersection; however, when Clip to Search Envelope is selected, a clipping operation is also performed in addition to the intersection.