1GMTGRAVMAG3D(1)                       GMT                      GMTGRAVMAG3D(1)
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NAME

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

10       gmtgravmag3d  -Tpxyz_file[+m]  -Tvvert_file OR  -Tr|sraw_file [  -Cden‐
11       sity  ]  [   -D  ]  [  -Ethickness ] [  -Fxy_file ] [  -Goutputgrid ] [
12       -Hf_dec/f_dip/m_int/m_dec/m_dip ] [  -Lz_observation ] [  -Sradius ]  [
13       -Zlevel ] [  -V[level] ] [ -fg]
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15       Note:  No  space  is allowed between the option flag and the associated
16       arguments.
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DESCRIPTION

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

25       -Cdensity
26              Sets  body density in SI. This option is mutually exclusive with
27              -H.
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29       -Hf_dec/f_dip/m_int/m_dec/m_dip
30              Sets  parameters  for  computing   a   magnetic   anomaly.   Use
31              f_dec/f_dip  to  set  the geomagnetic declination/inclination in
32              degrees. m_int/m_dec/m_dip are the body magnetic intensity  dec‐
33              lination and inclination.
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35       -Fxy_file
36              Provide  locations where the anomaly will be computed. Note this
37              option is mutually exclusive with -G.
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39       -Goutgrid
40              Output the gravity or magnetic anomaly at  nodes  of  this  grid
41              file.
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43       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
44              Specify the region of interest.
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46       -Tpxyz_file[+m] -Tvvert_file OR Tr|sraw_file
47              Gives  names  of xyz (-Tpxyz_file[+m]) and vertex (-Tvvert_file)
48              files defining a close surface.  The file formats correspond  to
49              the  output of the triangulate program.  The optional +m flag to
50              -Tp instructs the program that the xyzm file  has  four  columns
51              and  that the fourth column contains the magnetization intensity
52              (plus signal), which needs not to be constant. In this case  the
53              third  argument  of  the  -H  option  is  ignored.  A raw format
54              (selected by the -Tr option) is a file with N rows (one per tri‐
55              angle)  and  9 columns corresponding to the x,y,x coordinates of
56              each of the three vertex of each triangle.   Alternatively,  the
57              -Ts  option  indicates that the surface file is in the ASCII STL
58              (Stereo Lithographic) format.  These two type of files are  used
59              to provide a closed surface.
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OPTIONAL ARGUMENTS

62       -V[level] (more ...)
63              Select verbosity level [c].
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65       -E[thickness]
66              give  layer thickness in m [Default = 0 m]. Use this option only
67              when the triangles describe a non-closed surface  and  you  want
68              the anomaly of a constant thickness layer.
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70       -L[z_observation]
71              sets  level of observation [Default = 0]. That is the height (z)
72              at which anomalies are computed.
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74       -Sradius
75              search radius in km. Triangle centroids that  are  further  away
76              than  radius  from  current  output point will not be taken into
77              account.  Use this option to speed up computation at expenses of
78              a less accurate result.
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80       -Z[level]
81              level of reference plane [Default = 0]. Use this option when the
82              triangles describe  a  non-closed  surface  and  the  volume  is
83              defined  from each triangle and this reference level. An example
84              will be the hater depth to compute a Bouguer anomaly.
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86       -fg    Geographic grids (dimensions of  longitude,  latitude)  will  be
87              converted  to  meters via a "Flat Earth" approximation using the
88              current ellipsoid parameters.
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90       -^ or just -
91              Print a short message about the  syntax  of  the  command,  then
92              exits (NOTE: on Windows just use -).
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94       -+ or just +
95              Print  an extensive usage (help) message, including the explana‐
96              tion of any module-specific  option  (but  not  the  GMT  common
97              options), then exits.
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99       -? or no arguments
100              Print a complete usage (help) message, including the explanation
101              of all options, then exits.
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GRID DISTANCE UNITS

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

110       Suppose you ...
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112              gmt gmtgravmag3d ...
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SEE ALSO

115       gmt, grdgravmag3d, talwani2d, talwani3d
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REFERENCE

118       Okabe,  M., Analytical expressions for gravity anomalies due to polyhe‐
119       dral bodies and translation into magnetic  anomalies,  Geophysics,  44,
120       (1979), p 730-741.
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123       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
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1285.4.5                            Feb 24, 2019                  GMTGRAVMAG3D(1)
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