.. index:: ! talwani3d ********* talwani3d ********* .. only:: not man talwani3d - Compute geopotential anomalies over 3-D bodies by the method of Talwani Synopsis -------- .. include:: ../../common_SYN_OPTs.rst_ **talwani3d** [ *modeltable* ] [ |-A| ] [ |-D|\ *rho* ] ] [ |-F|\ **f**\ \|\ **n**\ \|\ **v** ] [ |-G|\ *outfile* ] [ |SYN_OPT-I| ] [ |-M|\ [**h**]\ [**v**] ] [ |-N|\ *trackfile* ] [ |SYN_OPT-R| ] [ |-Z|\ *level*\ \|\ *obsgrid* ] [ |SYN_OPT-V| ] [ |SYN_OPT-bi| ] [ |SYN_OPT-d| ] [ |SYN_OPT-e| ] [ **-fg** ] [ |SYN_OPT-i| ] [ |SYN_OPT-o| ] [ **-r** ] [ |SYN_OPT-x| ] |No-spaces| Description ----------- **talwani3d** will read the multi-segment *modeltable* from file or standard input. This file contains contours of a 3-D body at different *z*-levels, with one contour per segment. The segment header must contain the parameters *zlevel rho*, which states the *z* contour level and the density of this slice (individual slice densities may be overridden by a fixed density contrast given via **-D**). We can compute anomalies on an equidistant grid (by specifying a new grid with **-R** and **-I** or provide an observation grid with elevations) or at arbitrary output points specified via **-N**. Chose from free-air anomalies, vertical gravity gradient anomalies, or geoid anomalies. Options are available to control axes units and direction. Required Arguments ------------------ *modeltable* The file describing the horizontal contours of the bodies. Contours will be automatically closed if not already closed, and repeated vertices will be eliminated. .. _-I: .. include:: ../../explain_-I.rst_ .. _-R: .. |Add_-R| unicode:: 0x20 .. just an invisible code .. include:: ../../explain_-R.rst_ Optional Arguments ------------------ .. _-A: **-A** The *z*-axis should be positive upwards [Default is down]. .. _-D: **-D**\ *unit* Sets fixed density contrast that overrides any setting in model file, in kg/m^3. .. _-F: **-F**\ **f**\ \|\ **n**\ \|\ **v** Specify desired gravitational field component. Choose between **f** (free-air anomaly) [Default], **n** (geoid) or **v** (vertical gravity gradient). .. _-G: **-G**\ *outfile* Specify the name of the output data (for grids, see GRID FILE FORMATS below). Required when an equidistant grid is implied for output. If **-N** is used then output is written to stdout unless **G** specifies an output file. .. _-M: **-M**\ [**h**]\ [**v**] Sets units used. Append **h** to indicate horizontal distances are in km [m], and append **z** to indicate vertical distances are in km [m]. .. _-N: **-N**\ *trackfile* Specifies locations where we wish to compute the predicted value. When this option is used there are no grids and the output data records are written to stdout. .. _-V: .. |Add_-V| unicode:: 0x20 .. just an invisible code .. include:: ../../explain_-V.rst_ .. _-Z: **-Z**\ *level*\ \|\ *obsgrid* Set observation level either as a constant or give the name of a grid with observation levels. If the latter is used the the grid determines the output grid region [0]. .. |Add_-bi| replace:: [Default is 2 input columns]. .. include:: ../../explain_-bi.rst_ .. |Add_-d| unicode:: 0x20 .. just an invisible code .. include:: ../../explain_-d.rst_ .. |Add_-e| unicode:: 0x20 .. just an invisible code .. include:: ../../explain_-e.rst_ **-fg** Geographic grids (dimensions of longitude, latitude) will be converted to km via a "Flat Earth" approximation using the current ellipsoid parameters. .. |Add_-h| replace:: Not used with binary data. .. include:: ../../explain_-h.rst_ .. include:: ../../explain_-icols.rst_ .. include:: ../../explain_-ocols.rst_ .. |Add_nodereg| unicode:: 0x20 .. just an invisible code .. include:: ../../explain_nodereg.rst_ .. include:: ../../explain_core.rst_ .. include:: ../../explain_colon.rst_ .. include:: ../../explain_help.rst_ .. include:: ../../explain_distunits.rst_ Examples -------- To compute the free-air anomalies on a grid over a 3-D body that has been contoured and saved to body.txt, using 1.7 g/cm^3 as the density contrast, try :: gmt talwani3d -R-200/200/-200/200 -I2 -G3dgrav.nc body.txt -D1700 -Fg To obtain the vertical gravity gradient anomaly along the track in crossing.txt for the same model, try :: gmt talwani3d -Ncrossing.txt body.txt -D1700 -Fv > vgg_crossing.txt Finally, the geoid anomaly along the same track in crossing.txt for the same model is written to n_crossing.txt by :: gmt talwani3d -Ncrossing.txt body.txt -D1700 -Fn -Gn_crossing.txt References ---------- Kim, S.-S., and P. Wessel, 2016, New analytic solutions for modeling vertical gravity gradient anomalies, *Geochem. Geophys. Geosyst., 17*, `http://dx.doi.org/10.1002/2016GC006263 `_. Talwani, M., and M. Ewing, 1960, Rapid computation of gravitational attraction of three-dimensional bodies of arbitrary shape, *Geophysics, 25*, 203-225. See Also -------- :doc:`gmt.conf `, :doc:`gmt `, :doc:`grdmath `, :doc:`gravfft `, :doc:`gmtgravmag3d `, :doc:`grdgravmag3d `, :doc:`talwani2d `