Import/Export 导入/导出格式

SDTSDEM (.ddf)

SDTS GIS format.
Geographic information standard used by the U.S. Geological Survey.
Used for archiving and exchanging terrain data.
SDTS is an acronym for Spatial Data Transfer Standard.
Based on ISO 8211.
U.S. 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 elevation models (DEM).
Digital elevation models are stored as a raster of elevation values.

Import is fully compatible with the SDTSDEM file format.

Import can also read "SDTS" digital line graph files.

IMPORT

Import["dir", "SDTS"] or Import["dir"] imports an entire SDTSDEM directory and returns a combined rendering of all graphics layers.

Import["fileCATD.ddf"] explicitly specifies the main .ddf file of an SDTSDEM bundle to be imported.

Import["dir"] returns a Graphics object.

Import["dir", "elem"] imports the specified element from an SDTSDEM 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

General Import elements:

	"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

Data representation elements:

	"Graphics"	terrain data rendered as a ReliefPlot
	"Data"	array of elevation values

Import by default uses the "Graphics"element for the SDTSDEM format.

Metadata elements:

	"DataFormat"	type used to represent elevation values
	"ElevationRange"	range of elevation values in meters
	"RasterSize"	size of the terrain grid
	"SpatialRange"	range of geographic coordinates, given in coordinate system units
	"SpatialResolution"	grid spacing in coordinate system units

Import["file.dem", "ElevationRange"]gives the range {z_min, z_max}of elevation values in units of meters.

Import["file.dem", "SpatialRange"] gives the bounding coordinates of the geographic region covered by the file as an expression of the form {{lat_min, lat_max}, {long_min, long_max}}.

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

Elements specifying the cartographic projection and its parameters:

	"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"	Mathematica standard name of the projection used
	"ReferenceModel"	what reference sphere or ellipsoid to use

Accessing low-level metainformation 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.

OPTIONS

General rendering options:

Background	None	background color
DataRange	Automatic	the range of latitude and longitude values to assume for the data
ImageSize	Automatic	overall size of the image

DEM rendering options:

BoxRatios	Automatic	effective 3D bounding box ratios
ColorFunction	"Topographic"	how to determine the color of surfaces
DataReversed	False	whether to reverse the order of rows
LightingAngle	Automatic	the effective angle from which simulated illumination is taken to come

Import options:

	"DefaultElevation"	Automatic	elevation setting for areas not covered by the file
	"DownsamplingFactor"	1	integer factor by which the amount of DEM data in each horizontal dimension is reduced on import