NAME

       gmtgravmag3d - Compute the gravity/magnetic effect of a body by the method of Okabe

SYNOPSIS

       gmtgravmag3d  [[d]xyz_file/vert_file[/m]]|[r|s]raw_file  [  density ] [  ] [ thickness ] [
       xy_file ] [ outputgrid ] [ f_dec/f_dip/m_int/m_dec/m_dip ] [ z_observation ] [ radius ]  [
       level ] [ [level] ] [ -fg]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       gmtgravmag3d  will compute the gravity or magnetic anomaly of a body described by a set of
       triangles. The output can either be along a given set of xy locations or on a  grid.  This
       method  is  not  particularly fast but allows computing the anomaly of arbitrarily complex
       shapes.

REQUIRED ARGUMENTS

       -Cdensity
              Sets body density in SI. This option is mutually exclusive with -H.

       -Hf_dec/f_dip/m_int/m_dec/m_dip
              Sets parameters for computing a  magnetic  anomaly.  Use  f_dec/f_dip  to  set  the
              geomagnetic  declination/inclination  in  degrees.  m_int/m_dec/m_dip  are the body
              magnetic intensity declination and inclination.

       -Fxy_file
              Provide locations where the anomaly will be computed. Note this option is  mutually
              exlusive with -G.

       -Goutgrid
              Output the gravity or magnetic anomaly at nodes of this grid file.

       -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
              Specify the region of interest.

       -T[[d]xyz_file/vert_file[/m]]|[r|s]raw_file]
              Give  either  names  of  xyz[m] and vertex files or of a raw or stl file defining a
              close surface. In the first case append a d immediately after -T and  optionally  a
              /m  after  the  vertex  file name. In the second case append a r or a s immediately
              after -T and before the file name. A vertex file is a file with  N  rows  (one  per
              triangle) and 3 columns with integers defining the order by which the points in the
              xyz file are to be connected  to  form  a  triangle.  The  output  of  the  program
              triangulate  comes  in  this format. The optional /m instructs the program that the
              xyzm file has four columns and that the fourth column  contains  the  magnetization
              intensity  (plus  signal),  which  needs not to be constant. In this case the third
              argument of the -H option is ignored. A raw format (selected by the  r  flag  is  a
              file  with  N  rows  (one  per  triangle)  and 9 columns corresponding to the x,y,x
              coordinates of each of the three vertex of each  triangle.   Alternatively,  the  s
              flag  indicates  that  the  surface  file is in the ASCII STL (Stereo Lithographic)
              format. These two type of files are used to provide a closed surface.

OPTIONAL ARGUMENTS

       -V[level] (more ...)
              Select verbosity level [c].

       -E[thickness]
              give layer thickness in m [Default = 0 m]. Use this option only when the  triangles
              describe  a  non-closed  surface  and  you want the anomaly of a constant thickness
              layer.

       -L[z_observation]
              sets level of observation [Default = 0]. That is the height (z) at which  anomalies
              are computed.

       -Sradius
              search  radius  in  km.  Triangle  centroids that are further away than radius from
              current output point will not be taken into account.  Use this option to  speed  up
              computation at expenses of a less accurate result.

       -Z[level]
              level of reference plane [Default = 0]. Use this option when the triangles describe
              a non-closed surface and  the  volume  is  defined  from  each  triangle  and  this
              reference level. An example will be the hater depth to compute a Bouguer anomaly.

       -fg    Geographic  grids  (dimensions  of longitude, latitude) will be converted to meters
              via a "Flat Earth" approximation using the current ellipsoid parameters.

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              use just -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation of  options,  then
              exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

GRID DISTANCE UNITS

       If  the  grid  does not have meter as the horizontal unit, append +uunit to the input file
       name to convert from the specified unit to meter.  If your  grid  is  geographic,  convert
       distances to meters by supplying -fg instead.

EXAMPLES

       Suppose you ...

              gmt gmtgravmag3d ...

SEE ALSO

       gmt, grdgravmag3d, talwani2d, talwani3d

REFERENCE

       Okabe,  M.,  Analytical  expressions  for  gravity  anomalies due to polyhedral bodies and
       translation into magnetic anomalies, Geophysics, 44, (1979), p 730-741.

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe