NAME

     gridr  - interpolation/extrapolation of seismic data using a
     grid  reduction algorithm based on a surface coordinate sys-
     tem.  Good way to generate a 3D volume from  a  2D  dataset.
     May also be used to interpolate trace header information.

SYNOPSIS

     gridr [ -Nntap ] [ -Ootap ] [ -sist ] [ -eiend ] [ -xmaxxmax
     ]  [  -xminxmin  ] [ -ymaxymax ] [ -yminymin ] [ -dxxinc ] [
     -dyyinc ] [ -nzeronz ] [ -nsegsnseg ] [ -npnp ]  [  -radius-
     dist ] [ -hwword ] [ -3d ] [ -C ] [ -L ] [ -V ] [ -?  or  -h
     or  -help]

DESCRIPTION

     gridr : This routine implements a 2D sample-wise grid reduc-
     tion  of  the  input data onto a user defined grid of output
     locations.  It is suitable for generating  a  3D  volume  of
     data where previously only sparse 2D coverage existed.  Data
     should be flattened in advance of this procedure if signifi-
     cant  structure is present in order to avoid aliasing diffi-
     culties.  The routine may be used to fit either  trace  data
     or trace header data to the output grid.

     gridr gets both its data and  its  parameters  from  command
     line  arguments.  These arguments specify the input, output,
     the start and end time, the minimum  and  maximum  X  and  Y
     coordinates  for  the  output  grid,  the  X and Y grid node
     increments, the number of segments  in  the  grid  reduction
     operator,  the  maximum number of zero segments, the minimum
     number of data points per segment, the radius of  investiga-
     tion, an optional trace header mnemonic to grid reduce, a 3D
     data flag, a cosine or linear  weighting  flag  and  verbose
     printout, if desired.

  Command line arguments
     -N ntap  [default: NONE]
          Enter the input data set name or file immediately after
          typing  -N. This input file should include the complete
          path name if the file resides in a different directory.
          Example  -N/b/vsp/dummy  tells  the program to look for
          file 'dummy' in directory '/b/vsp'.  This routine  must
          move  a disk pointer around in the input file making it
          necessary that the input file reside on  disk.   Piping
          into this routine is not supported.

     -O otap  [default: stdout]
          Enter the output data  set  name  or  file  immediately
          after  typing -O. This output file is not required when
          piping the output to another process. The  output  data
          set also requires the full path name (see above).


     -s nstr  [default: 0]
          Enter a window start time if desired.

     -e netr  [default: end of trace]
          Enter a window end time if desired.

     -xmin xmin  [default: 0.]
          Enter the minimum X  coordinate  for  the  output  data
          grid.

     -xmax xmax  [default: 999999.]
          Enter the maximum X  coordinate  for  the  output  data
          grid.

     -ymin ymin  [default: 0.]
          Enter the minimum Y  coordinate  for  the  output  data
          grid.

     -ymax ymax  [default: 999999.]
          Enter the maximum Y  coordinate  for  the  output  data
          grid.

     -dx xinc  [default: 100.]
          Enter the grid node increment in the X  direction.  Use
          the same units as with -xmin and -xmax above.

     -dy yinc  [default: 100.]
          Enter the grid node increment in the Y  direction.  Use
          the same units as with -ymin and -ymax above.

     -nzero nz  [default: 4.]
          Enter the maximum  number  of  adjacent  zero  segments
          allowed  before output grid value is set to zero.  This
          parameter governs how the grid reduction algorithm per-
          forms  near  the edges of the data.  A small value here
          will result in a greater degree of extraplolation  into
          zones of sparse data.

     -nsegs ns  [default: 6.]
          Enter the number of segments to use at each grid  node.
          Each  segment  will  cover(360 / nsegs) degrees of arc.
          The default is to use six 60 degree bins.

     -np np  [default: 1.]
          Enter the minimum number of points to allow in  a  seg-
          ment before the contribution from the entire segment is
          set to zero.

     -radius dist  [default: 1000.]
          Enter the radius of investigation in the same units  as
          -xmin  etc.  above.   This  defines  the maximum offset
          within each segment  to  be  searched  for  input  data
          during grid reduction.

     -hw word   [default: grid the data not the header]
          Enter a valid USP trace header mnemonic whose value  is
          to  be  grid reduced to the user defined grid.  If this
          entry is used no attempt will be made to grid the data.
          Only  the specified header value will be gridded.  This
          option is in place as it is often  the  case  that  the
          data   and   headers   require   completely   different
          parameterisation for a successful grid reduction.   The
          most  facile  way  to  use this option is to generate a
          header dataset using  hdrstrip and use that dataset  as
          input  to  this  routine when working with the headers.
          Use the same grid description as the associated dataset
          [-xmin,  -xmax, -ymin, -ymax, -dx, -y].  After success-
          ful grid reduction of the headers  the  output  may  be
          swapped  with  the  headers of the grid reduced seismic
          dataset using  hdrswap .

     -3d  Enter the command line argument '-3d' to have the  pro-
          gram  reference  the trace header mnemonics  CDPBCX and
          CDPBCY  for the (x,y) coordinates of  the  input  data.
          If  this entry is not present the mnemonics  SrPtXC and
          SrPtYC  will be used.

     -C   Enter the command line  argument  '-C'  to  use  cosine
          weighting  [as a function of distance] within each grid
          segment during grid reduction.  If  this  flag  is  not
          present, linear distance weighting will be used.

     -V   Enter the command line argument '-V' to get  additional
          printout.

     -? or -h or -help
          Enter the command line argument '-?'  or  -h  or  -help
          to  get  online help.  The program terminates after the
          help screen is printed.

DISCUSSION

     This  program  employes  a  grid  reduction  algorithm  that
     centers  a segmented circle over each output grid node.  The
     number of segments in and  the  radius  of  the  circle  are
     defined  by  the user [see -nsegs -radius above].  All input
     datapoint that lie within a given segment are used to calcu-
     late  a  contribution  for  that  segment to the output grid
     value after first being weighted according to distance  from
     the  node.   Either  a  cosine  or  linear weighting will be
     applied [see -C above].  The user may specify that a certain
     number  of  datapoints  be present in a given segment before
     that segment may contribute anything to the output grid node
     value  [see -np above].  The user may also specify that if a
     certain number of adjacent segments are zero that  the  grid
     value shall be set to zero [see -nzero above].  In undertak-
     ing parameter testing it is usefull to limit the  number  of
     samples  [see  -s and -e above] as this routine can be quite
     time and CPU intensive when let loose on a real  data  prob-
     lem.   It  is  also a good idea to pre-calculate the size of
     your output dataset before launching a real  grid  reduction
     as an output 3D volume can get quite large quite quickly.

BUGS

     Unknown.

AUTHOR

     [P.G.A. Garossino: ATTC: 3932 -- October 1995]

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.