COMMENTS FOR GRD2VTK AND GRD2VTK_CART AND OTHER VTK RELATED AWK SCRIPTS

source: http://www-udc.ig.utexas.edu/external/becker/software/grd2vtk.tgz

author: thorsten becker, UT Austin, thwbecker@post.harvard.edu

contains code by Christian Moder - LMU, and "sphere" by Jon Leech

license: gnu public license, no guarantees whatsoever.

WARNING: research code, not well documented nor tested

$Id: README,v 1.1 2018/01/18 14:42:06 twb Exp twb $

Contains grd2vtk, grd2vtk_cart and a bunch of awk scripts

• gmtpoly2vtk.awk: converts GMT -m polygons to VTK

• hypo2vtk.awk: converts lon-lat-z-mag eq data to spheres in VTK

• vtk_make_beachball.awk: make VTK beach ball - from Christian Moder

• lonlatvevn2vtk.awk: converts ve vn velocities to VTK vectors

• grd2vtk and grd2vtk_cart

PURPOSE: convert single or a set of "3D" GMT/netcdf grd files to (e.g. paraview) VTK format

grd2vtk operates on geographic coordinate system, using global or regional grd files. For global grids, it extracts triangular/wedge elements at a given refinement using "sphere" tesselation of the sphere. For regional grids, it uses irregular hexahedrons.

grd2vtk_cart uses Cartesian, regular grids and creates a rectilinear VTK object

INSTALL: 1) unpack tar file

 2) place .awk scripts into your $AWKPATH/

 3) place scripts 

 grd2vtk grd2reg grd2inc oneline grd2max grd2absmax lc grd2nx grd2ny

 into your script directory (in your $PATH), and make executable 

 4) type "make" to compile helpers programs

 asciiint2bebin asciifloat2bebin sphere

 and place those in your $PATH

 The first two are for converting integers and floats to big
 endian binary format, the latter generates a spherical
 tesselation and is copyright by Jon Leech (leech @
 cs.unc.edu)
 
 5) read and modify the main grd2vtk and grd2vtk_cart scripts
    to adjust for the usage of the "sphere" output. the script
    assumes you have a bunch of sphere produced coordinates
    stored in files already.

USAGE: grd2vtk globaltopo.grd OR grd2vtk_cart dv

   see script comments and source for options

1. grd2vtk

For global grids, the grd2vtk script uses "sphere" by Jon Leech to generate a set of triangular elements on the surface of the sphere and then GMT grdtrack to extract scalars from the grd files. For regional grids, irregular hexes are extracted. Both data sets are then converted into vtk (either POLYDATA for a single grd, or UNSTRUCTURED_GRID for a set of 3D levels), making output binary big endian (small C programs to do that are included) or ascii.

the idea is that the grd files are geographic but removing -fg in the script should fix the global aspect. this script appears to work for global topography, e.g., or regional and global seismic tomography.

if GMT is installed properly, the script also produces a VTK version of a coast line file.

2. grd2vtk_cart

the grd2vtk_cart script relaxes the geographic assumption, and assumes that the grd files are Cartesian and creates a rectilinear vtk grid. it only works for sets of grds, not a single grid.

please read through the scripts to work out what they do, i don't have time right now to make this more user-friendly and documented. the script will have to be modified wrt. to the location of sphere's output, or the file I/O has to be replaced with a call to sphere on the fly.

if anyone finds this useful and fixes bugs or adds documentation, i'd appreciate an updated version.

hope this is helpful

thorsten

01/18/18