SDTS (.ddf)

Background

▪ SDTS GIS format.

▪ Geographic information standard used by the US Geological Survey.

▪ Used for archiving and exchanging maps and map data.

▪ SDTS is an acronym for Spatial Data Transfer Standard.

▪ Based on ISO 8211.

▪ US Federal Information Processing Standard.

▪ An SDTS transfer archive consists of multiple .ddf files, typically combined in a .tar.gz file.

▪ The file extension .ddf is derived from Data Descriptive File.

▪ Binary format.

▪ Contains digital line graphs (DLG).

▪ Digital line graphs are vector data commonly used for maps.

▪ Digital elevation models are stored as a raster of elevation values.

Import["dir","SDTS"] or Import["dir"] imports an entire SDTS directory and returns a combined rendering of all graphics layers.
Import["fileCATD.ddf"] explicitly specifies the main .ddf file of an SDTS bundle to be imported.
Import["dir"] returns a GeoGraphics object.
Import["dir","elem"] imports the specified element from an SDTS file.
Import["dir",{"elem","sub_a","sub_b",…}] imports a subelement.
Import["dir",{{"elem₁","elem₂",…}}] imports multiple elements.
See the reference pages for full general information on Import.

	"Elements"	list of elements and options available in this file
	"Rules"	full list of rules for each element and option
	"Options"	list of rules for options, properties, and settings

	"Graphics"	all layers combined into a single graphics object
	"GraphicsList"	list of graphics representing the layers of an SDTS archive
	"Data"	graphics primitives for each layer
	"SpatialRange"	range of geographic coordinates, typically given in decimal degrees

Import by default uses the "Graphics" element for SDTS bundles.
Import with element "Graphics" gives the combined graphics contents of an SDTS archive as a Graphics or GeoGraphics object.
Data representation elements:
"LayerNames" labels for each layer, given as a list of strings

"LayerTypes" SDTS data types for each layer
Elements representing the geodetic datum and reference ellipsoid used in the file:

	"CoordinateSystem"	name of the coordinate system used in the file
	"Datum"	geodetic datum
	"SemimajorAxis"	semimajor axis of the reference ellipsoid in meters
	"SemiminorAxis"	semiminor axis of the reference ellipsoid in meters
	"InverseFlattening"	inverse flattening of the ellipsoid
	"LinearUnits"	coordinate system units

	"Projection"	projection name and parameters
	"Centering"	latitude and longitude defining the origin of the projection
	"StandardParallels"	standard parallels
	"CentralScaleFactor"	scale factor at the central meridian or center of projection
	"GridOrigin"	grid coordinates {n,e} of the central parallel and meridian
	"ProjectionName"	Wolfram Language standard name of the projection used
	"ReferenceModel"	what reference sphere or ellipsoid to use

Accessing low-level meta-information from the file:
"CoordinateSystemInformation" raw parameters of the coordinate system as stored in the file
See the reference page for GeoProjectionData for full information on cartographic projections.