NAME
     HT - NMRPipe Hilbert Transform

SYNOPSIS
     nmrPipe -fn HT [-ps90-180 | -ps0-0 | -auto] [-nozf | -zf]

DESCRIPTION
     HT applies a Hilbert transform, which reconstructs the  ima-
     ginary  part  of a given spectrum to create a complex result
     from a real imput.  It leaves the  real  part  of  the  data
     unchanged.   The HT is commonly used in cases where the ima-
     ginary data have been deleted  during  previous  processing,
     but the data must be re-phased or inverse-processed.

     In order to reconstruct imaginary data  properly,  the  data
     must have been at least doubled in size by zero filling dur-
     ing previous Fourier processing. In addition,  if  the  data
     previously required substantial first-order phase correction
     (for instance because of a  substantial  acquisition  delay)
     the  HT  will  generate  results  which are distorted at the
     edges.   However,  if  the  acquisition  delay  was  set  to
     1/2-dwell  (P1=180),  this  problem  can  be  avoided  by  a
     mirror-image implementation of the HT.

OPTIONS
     -ps90-180
          This flag enables a mirror-image implementation of  the
          HT  suitable  for  data  with  a  1/2-dwell acquisition
          delay.

     -zf  This flag enables  use  of  temporary  zero-filling  to
          increase  the speed of the HT.  This option can only be
          used for the ordinary HT.

     -auto
          This flag enables automatic selection of  the  HT  type
          and  the temporary zero-fill mode.  If the given dimen-
          sion has a recorded first-order phase of 180.0, and  if
          it  is not an extracted region, mirror-image HT with no
          temporary zero-fill will be  selected.   Otherwise,  an
          ordinary  HT  will  be  used  with  temporary zero-fill
          enabled.

     -ps0-0
          This flag forces use of an ordinary HT. It is  used  to
          override automatic settings from the -auto option.

     -nozf
          This flag suppresses use of a temporary zero  fill.  It
          is  used  to override automatic settings from the -auto
          option.

EXAMPLES
     The following scheme demonstrates the HT used to reconstruct
     imaginary  data  so that the X-Axis of the given 2D spectrum
     can be rephased:


      nmrPipe -in test.ft2              \
      | nmrPipe -fn HT -auto            \
      | nmrPipe -fn PS -p0 90 -p1 0 -di \
         -out test.ft2 -inPlace -verb


     The following scheme demonstrates the HT used to reconstruct
     imaginary  data  so that the Y-Axis of the given 2D spectrum
     can be rephased:


      nmrPipe -in test.ft2              \
      | nmrPipe -fn TP                  \
      | nmrPipe -fn HT -auto            \
      | nmrPipe -fn PS -p0 90 -p1 0 -di \
         -out test.ft2 -inPlace -verb


     The following is a  general  2D  inverse  Fourier  transform
     scheme,  which  will regenerate a 2D hypercomplex FID from a
     real-only 2D spectrum.  Note  use  of  the  generic  nmrPipe
     option  -ad  to make room for hypercomplex data, and the use
     of the hypercomplex transpose option TP -hyper:


      nmrPipe -in test.ft2             \
      | nmrPipe -fn HT -auto -verb     \
      | nmrPipe -fn PS -inv -hdr       \
      | nmrPipe -fn FT -inv            \
      | nmrPipe -fn ZF -inv            \
      | nmrPipe -fn APOD -inv -hdr -ad \
      | nmrPipe -fn TP -hyper          \
      | nmrPipe -fn HT -auto -verb     \
      | nmrPipe -fn PS -inv -hdr       \
      | nmrPipe -fn FT -inv            \
      | nmrPipe -fn ZF -inv            \
      | nmrPipe -fn APOD -inv -hdr     \
         -out test.fid -ov


BUGS
     The HT will change the data  type  automatically  to  create
     complex  data  from all-real data, but it will not automati-
     cally create hypercomplex data from complex data.