From craver@clark.net Sat Apr 8 21:03:03 1995 Path: solitaire.cv.nrao.edu!hearst.acc.Virginia.EDU!caen!usenet.cis.ufl.edu!usenet.eel.ufl.edu!news.mathworks.com!news.duke.edu!godot.cc.duq.edu!toads.pgh.pa.us!hudson.lm.com!news.pop.psu.edu!news.cac.psu.edu!howland.reston.ans.net!news.sprintlink.net!news.clark.net!usenet From: Rob Craver II Newsgroups: sci.geo.geology,sci.data.formats Subject: Re: USGS Digital Elevation Maps data format Date: 7 Apr 1995 15:52:14 GMT Organization: Clark Internet Services, Inc. Lines: 181 Message-ID: <3m3n3e$sm5@clarknet.clark.net> References: NNTP-Posting-Host: craver-ppp.clark.net Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Xref: solitaire.cv.nrao.edu sci.geo.geology:18800 sci.data.formats:875 enrico.ballarin-dolfin@svusenet.ubs.ch wrote: > > Hi! > > I'm looking for the data format description of the USGS Digital Elevation Maps. > Does anybody have it? > > Thanks in advance! > > Enrico > > -- > Enrico Ballarin Dolfin > > email: enrico_ballarin_dolfin@macquality.ch > enrico@ezinfo.vmsmail.ethz.ch Here it is: 1-degree USGS Digital Elevation Models Type A Record Sample DEM Type A Logical Records-Reno, Nevada-California, Quadrangle (West Half) (1 degree) NJ11-01W 3 1 0 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3 2 4 -0 42840000000000D+06 0.140400000000000D+06 0.428400000000000D+.06 0.144000000000000D+06 -0.42480000000000D+06 0.14400000000000D+06 -0424800000000000D+06 0.14040000000000D+06 0.999000000000D+03 0.264100000000000D+04 0.0 00.300000E+010.300000E+010.100000E+01 1 1201 Data Element Content Explanation 1 NJ11-01W Quadrangle name field (144 characters); NJ11-01W is the designation for the DEM covering the west half of the Reno, Nevada-California, sheet. 2 3 DEM level code; 3 reflects processing by DMA which includes registration to planimetric features appearing on the source 1-degree. 3 1 Pattern code; 1 indicates a regular elevation pattern. 4 0 Planimetric reference system code; 0 indicates geographic coordinate system. 5 0 Zone code; there are no zones in the geographic system. Therefore, the zone code is set to zero. 6 0.0 Map projection parameters; all 15 fields are set to (15 sets of 0.0) zero for the geographic system and should be ignored. Presence of non-zero parameters are not related to the geographic coordinate system and should also be ignored. 7 3 Units code; 3 represents arc-seconds as the unit of measure for ground planimetric coordinates throughout the file. 8 2 Units code; 2 represents meters as the unit of measure for elevation coordinates throughout the file. 9 4 Number (n) of sides in the polygon which defines the coverage of the DEM file (usually equal to 4). 10 -0.4284...D+06, A 4,2 array containing the ground coordinates of 0.1404...D+06 the four corners of the DEM. In this case ........ translation from arc-seconds to degrees, minutes ........ and seconds yields: -119 00 0, 39 00 00; -119 00 -0.4248...D+06 00, 40 00 00; -118 00 00, 40 00 00; -118 00 00. 0.1404...D+06 39 00 00. 11 0.9990...D+06 Minimum and maximum elevations for the DEM. 0.2641...D+04 12 0.0 Counterclockwise angle from the primary axis of ground planimetric referenced to the primary axis of the DEM local reference system. 13 0 Accuracy code; 0 indicates that a record of accuracy does not exist and that no record type C will follow. 14 0.300000E+01 A three-element containing DEM spatial 0.300000E+01 resolution (x,y, z); set to 3, 3, 1; or 3, 6, 1; 0.100000E+01 or 3, 9, 1 depending on the latitude of the product. 15 1 1201 A two-element array containing the number of rows and columns of profiles in the DEM. The row value m is usually set to 1 as an indication that the arrays are actually one-dimensional profiles. The column value n set to 1,201 indicates that the DEM file consists of a total of 1,201 profiles. DEM Type B Logical Record-Reno, Nevada California, Quadrangle (West Half) (1 degree) 1 1 1201 1 -0.42480000000000D+06 0.1404000000000D+06 0.0 0.121000000000D+04 0.177200000000D+04 1538 1539 1539 1534 1529 1520 1513 1508 1501 1493 1488 1479 1475 1474 1473 1472 1469 1467 1466 1464 Data Element Content Explanation 1 1 1 Row and column identification number of the profile contained in this record; 1, 1 represents row 1, column 1, in the DEM data set. 2 1201 1 Number of rows (elevations) and columns in this profile; 1201, 1 indicates there are 1,201 elevations and 1 column in this profile. 3 -0.4284...D+06 Translated to the decimal, -428400.0 and 0.1404...D+06 140400.0 are the ground planimetric coordinates (arc-seconds) of the first elevation in the profile, thus computed equal to -119 and 39 degrees. 4 0.0 Elevation of local datum for the profile. Always zero for 1-degree DEM, the reference is mean sea level. 5 0.1212...D+04 Minimum and maximum elevations for the profile. 0.1772...D+04 6 1538 1539... An array of m x n elevations (m=1201, n=1) for ....... the profile expressed in units of measure of meters (record A, element 8, indicates meters as units of measure) above or below the local datum (record a, element 4). Elevation Model Data Elements Logical Record Type C Type Physical Record Format Data (FORTRAN ASCII Starting Ending Comment Element Notation) Format byte byte 1 Code indicating INTEGER*2 16 1 6 Code 1 = available availability of 0 = unavailable statistics in data element 2 2 RMSE of file's INTEGER*2 3I6 7 24 In some units as datum relative indicated by elements to absolute 8 and 9 of logical datum (x, y, z) record type A. 3 Sample size on INTEGER*3 I6 25 30 If 0, then accuracy which statistics will be assumed to be in data element estimated rather than 2 are based computed. 4 Code indicating INTEGER*2 I6 31 36 Code 1 = available availability of 0 = unavailable statistics in data element 5 5 RMSE of DEM INTEGER*2 3I6 37 54 In same units as data relative indicated by elements to file's 8 and 9 of logical datum (x, y, z) record type A. 6 Sample size on INTEGER*2 I6 55 60 If 0, then accuracy which statistics will be assumed to in element 5 be estimated rather are based than computed.