m.dem.extract(1)       Grass User's Manual	 m.dem.extract(1)



NNAAMMEE
       mm..ddeemm..eexxttrraacctt   -  Extracts  USGS  Digital Elevation Model
       (DEM) data from 1/2-inch magnetic tape.
       _(_G_R_A_S_S _D_a_t_a _I_m_p_o_r_t_/_P_r_o_c_e_s_s_i_n_g _P_r_o_g_r_a_m_)

SSYYNNOOPPSSIISS
       mm..ddeemm..eexxttrraacctt
       mm..ddeemm..eexxttrraacctt hheellpp
       mm..ddeemm..eexxttrraacctt   iinnppuutt==_n_a_m_e   oouuttppuutt==_n_a_m_e   bblloocckkssiizzee==_v_a_l_u_e
       ssttaarrtt==_v_a_l_u_e eenndd==_v_a_l_u_e

DDEESSCCRRIIPPTTIIOONN
       _m_._d_e_m_._e_x_t_r_a_c_t  extracts USGS Digital Elevation Model (DEM)
       elevation data that fits  into  the  user's  current  geo-
       graphic	region	from  the  input file _i_n_p_u_t, in blocks of
       _b_l_o_c_k_s_i_z_e bytes.  If no _i_n_p_u_t file  is  specified  by  the
       user,  input is taken from /dev/rmt0, by default.  Results
       are placed in the named _o_u_t_p_u_t file,  and  stored  beneath
       the   _c_e_l_l   directory	of  the  user's  current  mapset.
       _m_._d_e_m_._e_x_t_r_a_c_t will only extract data that fall within  the
       boundaries  of the user's current geographic region.  Data
       falling	 outside   this   region   will    be	 ignored.
       _m_._d_e_m_._e_x_t_r_a_c_t will not complain if the input file does not
       cover the entire geographic region.  The user  should  run
       _m_._d_e_m_._e_x_t_r_a_c_t  without  specifying output file (which only
       examines the input file) prior to extracting the  data  to
       determine  the  size  of the geographic region needed.  If
       the block size is unknown, run the command _m_._e_x_a_m_i_n_e_._t_a_p_e


       The user can run this program either non-interactively  or
       interactively.	The program will be run non-interactively
       if the user specifies program  arguments  on  the  command
       line, using the form:


       mm..ddeemm..eexxttrraacctt  iinnppuutt==_n_a_m_e  [[oouuttppuutt==_n_a_m_e] [[bblloocckkssiizzee==_v_a_l_u_e]
       [[ssttaarrtt==_v_a_l_u_e] [[eenndd==_v_a_l_u_e]



       Alternately, the user can simply type mm..ddeemm..eexxttrraacctt on the
       command	line,  without	program arguments.  In this case,
       the user will be  prompted  for	needed	parameter  values
       using the standard GRASS interface described in the manual
       entry for _p_a_r_s_e_r



   PPaarraammeetteerrss::
       iinnppuutt==_n_a_m_e
	      The full path name of  tape  device  or  file  from
	      which DEM data are to be extracted.
	      Default:	/dev/rmt0

       oouuttppuutt==_n_a_m_e
	      The name to be assigned to the output file contain-
	      ing raster DEM data extracted from 1/2-inch tape.

       bblloocckkssiizzee==_v_a_l_u_e
	      The physical block size  (record	length)  of  each
	      each record, in bytes.

	      _m_._e_x_a_m_i_n_e_._t_a_p_e
	       can be used to determine block size.

       ssttaarrtt==_v_a_l_u_e
	      First DEM quad to look at (default 1).

       eenndd==_v_a_l_u_e
	      Last DEM quad to look at (default 9999999).


NNOOTTEESS
       The user should check the boundaries and resolution of the
       current region setting (see _g_._r_e_g_i_o_n )  BBEEFFOORREE  extracting
       data,  since _m_._d_e_m_._e_x_t_r_a_c_t will only extract the data that
       falls within these boundaries and only use the set resolu-
       tion during extraction.


       WWaarrnniinngg:   This program assumes that the tape has OONNLLYY DEM
       data.  If the tape contains other files (DLG, for example)
       the  program  will not skip over them.  In this case, for-
       ward the tape to the first DEM file.  Use the  appropriate
       UNIX  commands  (mmtt  to forward the tapes past the non-DEM
       files, and dddd to extract and copy the  correct  files)  on
       the  tape  on another machine first to extract the non-DEM
       data from the tape.


       UUSSGGSS TTaappeess:  This version of _m_._d_e_m_._e_x_t_r_a_c_t is sensitive to
       formatting  errors.  If the format on a tape is wrong, the
       program exits with  the	error  message:  "The  file  with
       incorrect data format encountered ..."	Nevertheless, the
       program continues.  In this case, run the program  without
       specifying  input  files.  If the program exits again with
       the same error message, there is an inconsistency  in  the
       data format.


       The format error:  Each USGS Dem file consists of A and B,
       and sometimes C, records--
       type A record  header
       type B record  collection of profiles with various numbers
       of elevations
       type C record  accuracy


       This  new  version  of  _m_._d_e_m_._e_x_t_r_a_c_t cannot skip over any
       records to the end of a DEM file. It first determines  how
       many records there are in a file, reads those records, and
       then proceeds to the header (record A) of the  next  file.
       Thus  it is very important for the program to know whether
       or not there is a C record to be read at the end  of  each
       file.   This  information  is  given in the  file's header
       record (type A) which has a field set to 1 when a C-record
       exits, and to 0 when a C-record does not exist.


       In  some  DEM  files, the accuracy field is set to 0, even
       though a C-record does exist.  Because of this error, when
       the  program  tries  to	read the data, it will not try to
       read the C-record, but instead attempts to go  on  to  the
       next  file  and	read  its  header--a type A record.  This
       results in the format error because  type  A  records  and
       type  C records have different formats, and the program is
       trying to  read	a  type  A  record   when   the  tape  is
       presenting a type C record.


       When  this  format error in a file is encountered, forward
       the tape to the next file.



SSEEEE AALLSSOO
       _g_._r_e_g_i_o_n



       _m_._e_x_a_m_i_n_e_._t_a_p_e



       _r_._r_e_s_c_a_l_e



       _r_._s_u_p_p_o_r_t



       _p_a_r_s_e_r


AAUUTTHHOORR
       Andrew Heekin, U.S. Army Construction Engineering Research
       Laboratory


       Improvements to program code were made for GRASS 4.0 by
       David Satnik, Central Washington University


       Major  enhancements for GRASS 4.1 to allow the input to be
       a file or tape were made by
       Olga  Waupotitsch,   U.S.Army   Construction   Engineering
       Research Laboratory

       _L_a_s_t _c_h_a_n_g_e_d_: _$_D_a_t_e_: _2_0_0_2_/_0_1_/_2_5 _0_5_:_4_5_:_3_3 _$



GRASS 5.0					 m.dem.extract(1)
