readme

dem数据

1:24,000-Scale Raster Profile Digital Elevation Model Readme File  Version: 11/00 
(README)       

This directory contains a Spatial Data Transfer Standard (SDTS)-compliant 
raster profile transfer, produced by the National Mapping Program of the
U.S. Geological Survey (USGS).
  
If you have questions or comments, please send e-mail to [e-mail] 
or contact the USGS at:
	U.S. Geological Survey
	SDTS Task Force
	1400 Independence Road
	Rolla, MO 65401

PURPOSE OF TRANSFER:
        The mission of the USGS National Mapping Program is to meet the 
        Nation's need for basic geospatial data, ensuring access to and
	advancing the application of these data and other related earth 
        science information for users worldwide. These data are provided
	in SDTS format as the result of a Federal mandate.

        The digital elevation model (DEM) is the USGS National Mapping
	Program's response to the Nation's need for accurate and
	consistent geospatial digital elevation data in raster format.

STANDARD AUTHORITY:  
        American National Standards Institute (ANSI):
        Parts 1-3: ANSI NCITS 320-1998 The Spatial Data Transfer Standard
        Federal Geographic Data Committee:
	FGDC-STD-002.5-1999, February 1999
        Part 5: SDTS Raster Profile (RPE) with Basic Image Interchange
        Format (BIIF).

ISO 8211 CONFORMANCE:
        All files with extension *.DDF are in the ISO 8211 file transfer
        format. All SDTS spatial addresses are expressed in two 32-bit 
        binary subfields defined by the ISO 8211.  Files are Level 2 of
        ISO 8211.
 
CATALOG DIRECTORY MODULE xxxxCATD.DDF:
        Each transfer includes this catalog directory module that
        contains a listing of every SDTS ISO 8211 file included in the
        transfer (xxxx indicates a four-character transfer base that 
        is common to all files in a transfer).

IDENTIFICATION MODULE xxxxIDEN.DDF:
        This module contains information that describes the overall
        characteristics of the data in a transfer.

REFERENCES:
        "The Spatial Data Transfer Standard Mapping of the USGS Digital
        Elevation Model" describes SDTS transfers of DEM data, including
        detailed information on each module. The file can be downloaded
	from the SDTS FTP site:        
        ftp://sdts.er.usgs.gov/pub/sdts/datasets/raster/dem/

Additional information can be found on the SDTS Web site:
	http://mcmcweb.er.usgs.gov/sdts