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Mathematica Import/Export Format


Canadian digital elevation data.
Standard format for the distribution of terrain elevation data for the United States.
Canadian Centre for Topographic Information (CTI) standard.
ASCII format.
Typically distributed as a ZIP compressed file.
The .dem file extension is often omitted.
Stores elevation data as a 1201×1201 raster.
CDED is available in 1:50,000 and 1:250,000 scales.
The longitudinal grid spacing varies with the latitude of the geographic area.
1:50,000 CDED uses a grid spacing of 0.75×0.75 arc second, 0.75×1.5 arc second, or 0.75×3 arc second.
1:250,000 CDED uses a grid spacing of 3×3 arc second, 3×6 arc second, or 3×12 arc second.
Elevations are expressed in meters relative to mean sea level.
  • Import supports the CDED Level 1 standard.
  • Import["dir/"] imports a CDED directory and renders it as a topographic map.
  • Import[""] imports from a CDED archive file.
  • Import["dir/", elem] imports the specified element from CDED.
  • Import["dir/", {elem, suba, subb, ...}] imports a subelement.
  • Import["dir/", {{elem1, elem2, ...}}] imports multiple elements.
  • The import format can be specified with Import["file", "CDED"] or Import["file", {"CDED", elem, ...}].
  • When importing CDED topographic data, Mathematica reads information from multiple files contained in the CDED directory or archive file.
  • 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
"Data"array of terrain elevation values
"Graphics"CDED data rendered as ReliefPlot
  • Import by default uses "Graphics" for the CDED format.
  • Metadata elements:
"Dimensions"size of the elevation data array
"ElevationRange"range of elevation coordinates, given in meters
"ElevationResolution"resolution of elevation values, given in meters
"SpatialRange"range of geographic coordinates, given in decimal degrees
"SpatialResolution"grid spacing in arc seconds
  • Import["", "ElevationRange"]gives the range {zmin, zmax}of elevation values in units of meters.
  • Import["", "SpatialRange"]gives the bounding coordinates of the geographic region covered by the file as an expression of the form {{latmin, latmax}, {longmin, longmax}}.
BoxRatiosAutomaticeffective 3D bounding box ratios
ColorFunction"Topographic"how to determine the color of surfaces
DataRangeAutomaticthe range of latitude and longitude values to assume for the data
DataReversedFalsewhether to reverse the order of rows
ImageSizeAutomaticthe overall size of the image
LightingAngleAutomaticthe effective angle from which simulated illumination is taken to come
  • Advanced option:
"DownsamplingFactor"1integer factor by which the number of latitudinal and longitudinal data points is reduced when importing