430:(profiles) are a variable-length longitudinal column of raster elevations that start at a specified location. They are some multiple of 1024 bytes long and contain a small header summarizing the profile. The elevations are contiguous; breaks or other discontinuities are expressed using "void" elevations of value -32767. Each elevation is described as a six-character readable integer occupying a fixed location in a block. The profile header only appears in the first block, so subsequent blocks hold more elevation values. When reading the DEM file from first byte to last, one reads the profiles as columns from west to east. The elevations within a profile run from south to north. The variable-location and variable-length nature of profiles stems mainly from the use of the UTM (
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The USGS DEM format is a self-contained (single file) set of ASCII-encoded (text) 1024-byte (1024 ASCII chars) blocks that fall into three record categories called A, B, and C. There is no cross-platform ambiguity since line ending control codes are not used, and all data including numbers is
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fields hold the origin, type, summary statistics and the measurement systems used by the profiles. The A record appears once as the file's header, the C record also appears once as the trailer, and multiple B records (called
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Created from DLG that have vertically integrated with all categories of hypsography, hydrography, ridge line, break line, drain files, and all vertical and horizontal control network
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format but the format remains popular due to large numbers of legacy files, self-containment, relatively simple field structure and broad, mature software support.
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A USGS DEM can be classified into one of four levels of quality. This is due to the multiple methods of data collection, and certainty in the data.
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represented in readable text form. There is no known binary analogue of the format, although it is common practice to compress the files with
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May be derived from a wide variety of sources using any of a number of USGS approved techniques and instrumentation
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programs need to swap the "D" exponent-indicating character with "E" when parsing (and vice versa when writing).
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features to a level of detail similar to manual interpolations of information from printed source maps
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contain root-mean squared error (RMSE) quality control data, using ten six-character integer fields.
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The process includes all additional post-processing required to bring the DEM grid to its final form
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452:, U.S. Department of the Interior, U.S. Geological Survey, National Mapping Division (1992):
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The accuracy and data spacing are intended to support computer applications that analyze
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43:, and is used throughout the world. It has been superseded by the USGS's own
108:(DLG) contours or equivalent, from any USGS map series up to 1:100000 scale
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Unit of resolution of ground grid (0=radian;1=feet;2=metre;3=arc-second)
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129:Requires a system of logic to interpret the data
278:Unit of resolution Elevation (1=feet;2=metre)
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90:or manual profiling from aerial photographs
223:Descriptive Name of the represented area
170:Floating-point numbers are encoded using
481:Canadian Digital Elevation Data, Level 1
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410:Resolution per grid cell North – South
450:Standards for digital elevation models
399:Resolution per grid cell East – West
388:Maximum elevation found in this file
377:Minimum elevation found in this file
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366:Northing of the South East corner
344:Northing of the North East corner
322:Northing of the North West corner
300:Northing of the South West corner
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355:Easting of the South East corner
333:Easting of the North East corner
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289:Easting of the South West corner
503:United States Geological Survey
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466:Part 3: Quality control (1992)
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461:Part 2: Specifications (1995)
432:Universal Transverse Mercator
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471:Errata and changes (1998)
508:Digital elevation models
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477:Sources for USGS DEMs:
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456:Part 1: General (1992)
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67:Production process
421:Number of columns
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212:Description
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137:All series
123:7.5-minute
101:All series
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39:. It is an
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492:Categories
195:quadrangle
83:30-minute
61:DEM level
22:geospatial
438:C records
428:B records
70:Comments
51:DEM Level
191:profiles
186:A record
134:Level 4
120:Level 3
98:Level 2
75:Level 1
18:USGS DEM
172:Fortran
35:-based
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