Mathematica Import/Export Format

GTOPO30

GTOPO30 global topographic data.
United States Geological Survey (USGS) standard.
Distribution format for a global digital elevation model (DEM) with 30-arc-second grid spacing.
Binary format.
Typically distributed as a compressed archive of multiple files.
Uses a horizontal grid spacing of 30 arc seconds (1/120 degrees) or approximately 1 kilometer.
Developed 1993-1996 by the USGS Center for Earth Resources Observation and Science.

Import fully supports the GTOPO30 format.

IMPORT

Import["dir/"] imports a GTOPO30 directory and renders it as a topographic map.

Import["file.tar.gz"] imports from a GTOPO30 archive file.

Import["dir/"] renders GTOPO30 data using ReliefPlot.

Import["dir/", elem] imports the specified element from GTOPO30 data.

Import["dir/", {elem, sub_a, sub_b, ...}] imports a subelement.

Import["dir/", {{elem₁, elem₂, ...}}] imports multiple elements.

The import format can be specified with Import["file", "GTOPO30"] or Import["file", {"GTOPO30", elem, ...}].

When importing GTOPO30 topographic data, Mathematica reads information from multiple files contained in the GTOPO30 directory or archive file.

See the reference pages for full general information on Import.

ImportString supports the GTOPO30 format.

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

Import elements:

	"Data"	array of terrain elevation values
	"Graphics"	GTOPO30 data rendered as ReliefPlot

Import by default uses "Graphics" for the GTOPO30 format.

Metadata elements:

	"DataFormat"	data type used in the file for storing elevation values
	"Dimensions"	size of the elevation data array
	"SpatialRange"	range of geographic coordinates, given in decimal degrees
	"SpatialResolution"	grid spacing in arc seconds

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

Import["file.tar.gz", "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}}.

OPTIONS

General Import options:

BoxRatios	Automatic	effective 3D bounding box ratios
ColorFunction	"Cartographic"	how to determine the color of surfaces
ColorFunctionScaling	False	whether to normalize the elevation values supplied to the color function
DataRange	Automatic	the range of latitude and longitude values to assume for the data
DataReversed	False	whether to reverse the order of rows
ImageSize	Automatic	the overall size of the image
LightingAngle	Automatic	the effective angle from which simulated illumination is taken to come

Advanced options:

	"DefaultElevation"	0	elevation value taken for sea-level data points
	"DownsamplingFactor"	10	integer factor by which the number of latitudinal and longitudinal data points is reduced when importing

GTOPO30 internally represents the ocean elevation as meters.