Licensing options for this format begin with FME Professional Edition.
The United States Geological Survey (USGS) Digital Elevation Map (DEM) Reader/Writer module enables FME to read and write data in the USGS DEM format. This format is documented by the National Mapping Division (NMP) of the USGS.
The USGS NMP standards on the USGS DEM format can be found at:
http://nationalmap.gov/standards/demstds.html
Overview
There are five primary types of USGS DEM data according to the USGS NMP standard. The FME is capable of reading all of them.
A USGS DEM file is organized into three logical record types: A, B, and C. The type A record contains information that defines the general characteristics of the DEM. There is only one type A record per DEM file. The type B record contains profiles of elevation data and associated header information. There is a type B record for each profile. The type C record contains statistics on the accuracy of the data.
All USGS DEM files should adhere to 1998 USGS DEM Standards. However, please note that if the Suspect and Void Area Flag and the Horizontal Datum fields are not given values in record A, then warnings will be displayed in the log file and default values will be assigned. The Suspect and Void Area Flag field will be given the value of 0, meaning “none,” and the Horizontal Datum field will be given the value 1, representing NAD 27.
Vertical datum elevation values are also given is the USGS fact sheet US GeoData Digital Elevation Models (http://pubs.usgs.gov/fs/2000/0040/report.pdf) which states:
“Elevation values for the continental United States and Alaska are in reference to the National Geodetic Vertical Datum of 1929 (NGVD 29) with values for the islands of Hawaii, Puerto Rico, and Guam referenced to local mean sea level.”
Reader Overview
The FME considers a single USGS DEM file to be a dataset. USGS DEM files are raster files containing elevation data.
All the elevation samples in the file are translated to a three-dimensional (3D) FME raster feature. Optionally, using the Read as DEM Raster parameter, each elevation sample in the file can be translated to 3D FME point features.
Writer Overview
The USGS DEM writer creates and writes feature data to a USGS DEM folder specified by the Writer Dataset parameter.
The names of the USGS DEM output files written to the output dataset folder are determined from the fme_raster_filename attribute or from the FME feature type. The folder need not exist before the translation occurs. Any old USGS DEM files in the folder with the same name are overwritten with the new feature data. The USGS DEM writer distinguishes duplicate output files by appending numbers to the filenames.
FME currently supports writing to the following horizontal datum, projections, and units. Please note that certain combinations of the following may be invalid.
Horizontal Datum: NAD 27, WGS 72, WGS 84, NAD 83
Projections: LL, UTM (TM)
Units: RADIAN, FOOT, METER, SECOND
FME Raster Features
FME raster features represent raster data and use several concepts that are unlike those used in the handling of vector data. The topics below describe how FME processes raster data.
USGS DEM only supports rasters with a single numeric band.