NAME

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

SYNOPSIS

       gmtgravmag3d   -Tpxyz_file[+m]   -Tvvert_file OR  -Tr|sraw_file [  -Cdensity ] [  -D ] [  -Ethickness ] [
       -Fxy_file ] [  -Goutputgrid ] [  -Hf_dec/f_dip/m_int/m_dec/m_dip ] [  -Lz_observation ] [  -Sradius  ]  [
       -Zlevel ] [  -V[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 exclusive  with
              -G.

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

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more …)
              Specify the region of interest.

       -Tpxyz_file[+m] -Tvvert_file OR Tr|sraw_file
              Gives  names  of  xyz  (-Tpxyz_file[+m]) and vertex (-Tvvert_file) files defining a close surface.
              The file formats correspond to the output of the triangulate program.  The optional +m flag to -Tp
              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 -Tr option) 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 -Ts option 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 just use -).

       -+ 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 all options, then exits.

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

       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.3                                             Jan 03, 2018                                GMTGRAVMAG3D(1gmt)