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grdgravmag3d(1)                       GMT                      grdgravmag3d(1)


       grdgravmag3d  -  Compute  the gravity effect of a grid by the method of


       grdgravmag3d grdfile_top [grdfile_bot] [  -Cdensity ] [   -Ethick  ]  [
       -Fxy_file  ] [  -Goutgrid ] [  -H<^<i>a|> ] [  -Iincrement ] [  -Lz_obs ] [
       -Q[nn_pad]|[pad_dist]|[<w/e/s/n>] ] [   -Rregion  ]  [   -Sradius  ]  [
       -V[level] ] [  -Zlevel[b|t] ] [ -fg ] [ -x+a|n|-n ]

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


       grdgravmag3d will compute the gravity anomaly of a  body  described  by
       one  or  (optionally)  two grids 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.


       grdfile_top [grdfile_bot]
              Grid  file  whose gravity effect is going to be computed. If two
              grids are provided then the gravity/magnetic effect of the  vol-
              ume between them is computed.

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

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

              Output the gravity anomaly at nodes of this grid file.


              To provide the layer thickness in m [Default = 500 m].

       -Hf_dec/f_dip/m_int/m_dec/m_dip        -H+m<magfile>        -Hx|y|z|h|t
              Sets parameters for computation of magnetic anomaly (Can be used
              multiple times).
                 f_dec/f_dip -> geomagnetic declination/inclination

                 m_int/m_dec/m_dip   ->   body   magnetic   intensity/declina-

              OR for a grid mode
                 +m<magfile>  where  amagfilea  is  the  name  of the magnetic
                 intensity file.

              To compute a component, specify any of:
                 x|X|e|E  to compute the E-W component.

                 y|Y|n|N  to compute the N-S component.

                 z|Z      to compute the Vertical component.

                 h|H      to compute the Horizontal component.

                 t|T|f|F  to compute the total field.

                 For a variable inclination and declination use IGRF. Set  any
                 of -H+i|+g|+r|+f|+n to do that

              x_inc  [and  optionally  y_inc] is the grid spacing. Optionally,
              append a suffix modifier.  Geographical  (degrees)  coordinates:
              Append  m  to indicate arc minutes or s to indicate arc seconds.
              If one of the units e, f, k, M, n or u is appended instead,  the
              increment  is assumed to be given in meter, foot, km, Mile, nau-
              tical mile or US survey foot, respectively,  and  will  be  con-
              verted  to  the equivalent degrees longitude at the middle lati-
              tude of the region (the conversion depends  on  PROJ_ELLIPSOID).
              If  y_inc is given but set to 0 it will be reset equal to x_inc;
              otherwise it will be converted to degrees latitude. All  coordi-
              nates:  If +e is appended then the corresponding max x (east) or
              y (north) may be slightly adjusted  to  fit  exactly  the  given
              increment  [by default the increment may be adjusted slightly to
              fit the given domain]. Finally, instead of giving  an  increment
              you  may  specify the number of nodes desired by appending +n to
              the supplied integer argument; the increment  is  then  recalcu-
              lated  from  the  number  of nodes and the domain. The resulting
              increment value depends on whether you  have  selected  a  grid-
              line-registered  or  pixel-registered grid; see App-file-formats
              for details. Note: if -Rgrdfile is used then  the  grid  spacing
              has already been initialized; use -I to override the values.

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


              Extend the domain of  computation  with  respect  to  output  -R
                     -Qnn_pad artificially extends the width of the outer  rim
                     of cells to have a fake width of n_pad * dx[/dy].

                     -Qpad_dist  extend the region by west-pad, east+pad, etc.

                     -Qregion Same syntax as -R.

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
              Specify the region of interest. Note: this overrides the  source
              grid region (Default: use same region as input)

              Set  search  radius  in  km (valid only in the two grids mode OR
              when -E) [Default = 30 km].  This option serves to speed up  the
              computation  by not computing the effect of prisms that are fur-
              ther away than radius from the current node.

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

              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 water depth to compute a Bouguer anomaly. Use -Zb or
              Zt to close the body at its bottom (for example, to compute  the
              effect  of  a  dome)  or  at its top (to compute the effect of a

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

              Choose the number of processors used  in  multi-threading  (Only
              available with multi-threading builds).
                 +a Use all available processors.

                 n  Use n processors (not more than max available off course).

                 -n Use (all - n) processors.

       -^ 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 explana-
              tion 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.


       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


       Suppose  you  want  to compute the gravity effect of the phantom aSandy
       Islanda together with its not phantom seamount

              gmt grdgravmag3d sandy_bat.grd -C1700 -Z-4300 -fg -I1m -Gsandy_okb.grd -V

       To compute the vertical component due  to  a  magnetization  stored  in
       mag.grd over a zone defined by the surface bat.grd, using variable dec-
       lination and inclination provided the the IGRF and using 4  processors,

              gmt grdgravmag3d bat.grd -E10000 -Gcomp_Z.grd -Hz -H+n -H+mmag.grd -x4 -V -S50


       gmt(1), gmtgravmag3d(1), talwani2d(1), talwani3d(1)


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


       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.2                            Jun 24, 2017                  grdgravmag3d(1)

gmt5 5.4.2 - Generated Wed Jun 28 19:20:11 CDT 2017
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