User's Guide

DEMENTER

Read DEM, DTT, or DTED format tapes into LAS

Function:

Reads elevation data from magnetic tapes or disk in IBM variable or variable block spanned formats that contain either Binary or ASCII data.

The program accepts DEM data in a uniform array of patches one row high and each patch is one column high. A patch is defined as a four-sided polygon containing a regular pattern of elevation data. Only this type of data has been produced to date, and no further development is anticipated.

Parameters:

COMMENT
Description of tape. A description of the tape to be used. The comment is sent to the operator's terminal when the tape is mounted. All files to be read in must be on the same tape. If set to null (--), the elevation data will be read from disk using the file names specified in INFILE.

OUT
Output images. The output data type is INTEGER*2 or REAL*4 as determined by the header record data. The output image size and data type are displayed to the user after the header record has been read. The header information for each image is also placed in an optional labeled table.

FILENUM
File numbers. The numbers of the files to be read. The user should note that the header records should not be included in the count when deciding upon the number of the file to be read. Only the data records should be counted. The number of values specified for FILENUM must be equal to the number of values specified in OUT and OUTLT when reading from tape and must be in ascending order. FILENUM is ignored when reading from disk.

FTYPE(DEM)
File type. The type of elevation data file on the tape. Three types of input data are possible. 


  = DEM:   Digital elevation model 
           Binary: 
           - usually labeled with a blocksize of 32760
           - unlabeled with a blocksize of 4096
           ASCII:  
           - usually unlabeled with a blocksize of 4096
           - unlabeled with a blocksize of  8192
           - unlabeled with a blocksize of 30720
           - unlabeled with a blocksize of 32760
  = DTT:   Digital terrain tape 
           - also called DMA tape
           - usually labeled with a blocksize of 32760
  = DTED:  Digital terrain elevation data
           - always labeled, always blocksize 2414

BACKGRND(0)
Background value. The background value used to designate areas that does not represent actual data.

OUTLT(--)
Output labeled table. The output labeled table file will contain the header information of each of the corresponding input files. If specified, the values for OUTLT must be equal to the number of values specified for OUT and FILENUM.

PRINT(TERM)
Output destination. The destination of the output. 


  = --:        No Report
  = TERM:      Terminal.  Output is sent to the user's
               terminal.
  = LP:        Line printer.  Output is sent to the 
               printer defined by $PRINTER.
  = Filename:  User-supplied filename.  Output is 
               sent to the user-supplied file with 
               the extension ".prt".

INFILE(--)
Input file(s). The input DEM disk file containing the elevation data. INFILE is ignored if COMMENT is specified.

Examples:

  1. LAS> dementer comment="tape number el1942" out=demimg filenum=1 ftype=dem backgrnd=1 outlt=demlt print=term

    Tape EL1942 will be mounted on an available tape drive. The specified tape contains DEM data, and the first file on the tape will be written to a LAS output image named DEMIMG. The header information will be read into a labeled table file called DEMLT. Information about the DEM data will be printed to the terminal.

  2. LAS> dementer comment="please mount tape hh9087" out=(dttimg1,ddtimg2) filenum=(2,5) ftype=dtt print=lp

    Tape HH9087 will be mounted on an available tape drive. The specified tape contains DTT data. The second file on the tape will be written to a LAS output image named DTTIMG1, and the fifth file on the tape will be read into a LAS output image named DTTIMG2. Information about the DTT data will be printed at the line printer.

  3. LAS> dementer comment="mount tape tt756" out=dtedimg filenum=3 ftype=dted backgrnd=250 outlt=dtedlt print=term

    Tape TT756 will be mounted on an available tape drive. The specified tape contains DTED data, and the third file on the tape will be written to a LAS output image named DTEDIMG. The header information will be saved into a labeled table file called DTEDLT. Information about the DTED data will be printed to the terminal.

  4. LAS> dementer comment=-- out=dtedimg filenum=-- ftype=dted outlt=dtedlt print=term infile=[w0530000]n470000;dt1

    The DEM file [W0530000]N470000;DT1 contains DTED data, and will be written to a LAS image named DTEDIMG. The header information will be saved in a labeled table file called DTEDLT. Information about the DTED data will be printed to the terminal.

Description/Algorithm:

The input data on the tape contains three types of records: A, B, and C. The "A" record contains the header information for the file. The "B" data records each contain one patch of data. A patch is defined as a four-sided polygon containing a regular pattern of elevation data. (See User Note 1.) The records contain header information for the patch and the data records. The "C" data record (if it exists) contains statistical data on the accuracy of the elevation data. If the input data is on disk, the A, B, and C records are stored in the file specified by INFILE.

The program converts the data elements from IBM to host machine format and builds a LAS image file from the data elements in the "B" records. The information from the "A" and "C" records is stored in a labeled table (LT) file and is displayed to the user at the end of the program and, if specified, written to a labeled table file.

Nonfatal Error Message:

    None.

Fatal Error Messages:

  1. [dementer-alloc] Error allocating dynamic memory

    An error was encountered while trying to allocate dynamic memory. See the System Manager.

  2. [dementer-block] A blocksize error while reading ASCII data

    A blocksize error was encountered while reading ASCII data. Verify the block sizes of the tape.

  3. [dementer-convert] Error encountered converting data

    An error was encountered trying to convert the data to the format of the host operating system. Verify that the operating system is supported by LAS.

  4. [dementer-data] Data set too large

    The data set is too large for the buffer space of DEMENTER. Verify that the format of the tape is supported by DEMENTER.

  5. [dementer-datum] Datum not WGS84, check the header

    The datum is not WGS84. Check to make sure the header has the correct datum and continue. See User Note #5.

  6. [dementer-fatal] Fatal error encountered

    A fatal error was encountered during processing. Processing is terminated. The error message that is displayed immediately preceding this message is the specific error that was encountered.

  7. [dementer-fclose] Error closing file <xxxx>

    An error was encountered while attempting to close input file xxxx. Check the input file.

  8. [dementer-filenum] The file numbers must be in ascending order

    The files must be read sequentially from tape. Respecify the FILENUM to be in the correct order.

  9. [dementer-fopen] Error opening file <xxxx>

    An error was encountered while attempting to open input file xxxx. Verify the input file name.

  10. [dementer-format] Data cannot be interpreted in <XXX> format

    The data being read from the tape cannot be interpreted as <XXX> data. Verify that the tape is in this format.

  11. [dementer-fread] Error encountered reading disk

    An error was encountered while attempting to read the input file. Verify the input file.

  12. [dementer-random] Random data patterns are not supported

    DEMENTER does not support random data patterns. See User Notes for more information.

  13. [dementer-read] Error reading data

    An error occurred reading the data in a specified format. Verify that the format of the tape is supported by DEMENTER.

  14. [dementer-skip] An error occurred skipping to a specified <XXXX> on tape

    An error was encountered while attempting to skip to the <XXXX> number. Verify that there is FILENUM number of files of the tape.

  15. [dementer-system] Error retrieving current system

    An error occurred retrieving the current operating system. This is needed in order to convert the binary data to the correct format. Check the preceding message for a more detailed description of the error.

  16. [dementer-tpclose] Error closing tape

    An error was encountered while attempting to close the tape. Check the tape drive.

  17. [dementer-tpopen] Error opening tape

    An error was encountered while attempting to open the tape. Verify the tape number or tape drive.

  18. [dementer-tpread] Error encountered reading tape

    An error was encountered while attempting to read the tape. Verify the tape number or the tape drive.

  19. [dementer-twodim] Two dimensional data is not supported

    DEMENTER does not support two-dimensional data. DEMENTER only supports single-dimensioned data.

  20. [dementer-values] The number of OUT, FILENUM and OUTLT values must be equal

    The number of output image names and the number of file numbers specified do not match. Respecify the OUT or FILENUM or OUTLT parameters.

  21. [dementer-values] The number of INFILE and OUT values must be equal

    The number of output image names and the number of input file names do not match. Respecify the OUT or INFILE parameters.

  22. [dementer-values] Parameters COMMENT or INFILE must be specified

    COMMENT must be specified if the user wants to read the data from tape. Otherwise, INFILE contains the names of the input data file used.

User Notes:

  1. The program DEMENTER accepts only data in a uniform distribution, where the array of patches is one row high and each patch is one column high. Only this type of data has been produced to date, and no further development is anticipated.

  2. For further information on DEM and DTT data, consult the Geological Survey Circular 895-B, entitled U.S.G.S. Digital Cartographic Data Standards for Digital Elevation Models. For information on DTED data, consult the Defense Mapping Agency's publication PS/ICD/200,PS/ICF/200, entitled Defense Mapping Agency Product Specification for Digital Terrain Elevation Data.

  3. Elevation data types currently available: 

    
    SCALE          COVERAGE                      DESCRIPTION
    =====          ========                      ===========
DTT 
___
 1:250,000      Most of Alaska           200 ft.(63.5 m) cell size
 1 x 1 degree   All of continental U.S.  UTM projection
 2 or 3 files   production finished      Elevation in feet
 Per map sheet                           ~1760 lines x 1450 samples
                                        (~850 samples in Alaska)

DEM 
___
 1:250,000      Most of Alaska           3 x 3 arcsecond cell size
 1 x 1 degree   90% of continental U.S.  (3 x 6 in Alaska)
 2 or 3 files   On-going effort; all     No projection
 Per map sheet  existing data in EDC     Elevation in meters
                tape library             1201 lines x 1201 samples
                                         (601 samples in Alaska)

DEM 
___
 1:24,000       10% of U.S.              30 meter cell size
 7.5 x 7.5 min. On-going effort          UTM projection
 1 file per                              Elevation in meters
 map sheet                               ~475 lines x 335 samples


Note: All formats rotated clockwise 90 degrees from north; line
      and sample numbers are after rotation to true north.

  4. To read the elevation data from disk, the user must set the COMMENT to null (--) and specify the input data file with INFILE . FILENUM is ignored. Currently, only the DEM and DTED formats are supported.

  5. According to the Department of Defense Performance Specification Digital Terrain Elevation Data document, the datum must be WGS84.