Vector Field File Format Conversion: avf2ovf

The avf2ovf program converts vector field files from any of the recognized formats (OVF, VIO) into the OVF format.

Launching
The avf2ovf launch command is:

tclsh oommf.tcl avf2ovf [standard options] \
   [-clip xmin ymin zmin xmax ymax zmax] [-flip flipstr] \
   [-format <text|b4|b8>] [-grid <rect|irreg>] [-info] [-keepbb] \
   [-mag] [-ovfversion version] [-pertran xoff yoff zoff] [-q] \
   [-resample xstep ystep zstep order] [-rpertran rxoff ryoff rzoff] \
   [-subsample period] [infile [outfile]]

where

-clip xmin ymin zmin xmax ymax zmax

The 6 arguments specify the vertices of a bounding clip box. Only mesh points inside the clip box are brought over into the output file. Any of the arguments may be set to ``-'' to use the corresponding value from the input file, i.e., to not clip along that box face.

-flip flipstr

Provides an axis coordinate transformation. Flipstr has the form A:B:C, where A, B, C is a permutation of x, y, z, with an optional minus sign on each entry. The first component A denotes the axis to which x is mapped, B where y is mapped, and C where z is mapped. The default is the identity map, x:y:z. To rotate 90^o about the z-axis, use ``-flip y:-x:z'', which sends x to the + y axis, y to the -x axis, and leaves z unchanged.

-format <text|b4|b8>

Specify output data format. The default is ASCII text; b4 selects 4-byte binary, b8 selects 8-byte binary. (The OVF format has an ASCII text header in all cases.)

-grid <rect|irreg>

Specify output grid structure. The default is rect, which will output a regular rectangular grid if the input is recognized as a regular rectangular grid. The option ``-grid irreg'' forces irregular mesh style output.

-info

Instead of converting the file, print information about the file, such as size, range, and descriptive text from the file header.

-keepbb

If the -clip option is used, then normally the spatial extent, i.e., the boundary, of the output is clipped to the specified clip box. If -keepbb (keep bounding box) is given, then the spatial extent of the output file is taken directly from the input file. Clipping is still applied to the data vectors; -keepbb affects only the action of the clip box on the boundary.

-mag

Write out a scalar valued field instead of a vector value field, where the scalar values are the magnitude | v(r)| of the vector values at each point r.

-ovfversion version

Specify the output OVF version, either 1 (default) or 2.

-pertran xoff yoff zoff

Translates field with respect to location coordiates, by amount (xoff, yoff, zoff), in a periodic fashion. For example, if (xoff, yoff, zoff) is (50e-9, 0, 0), then a vector v at position (rx, ry, rz) in the original file is positioned instead at (rx + 50e-9, ry, rz) in the output file. If the spatial extent of the x coordinate in the input file runs from xmin to xmax, and if rx + 50e-9 is larger than xmax, then v will be placed at rx + 50e-9 - xmax + xmin instead. Translations are rounded to the nearest full step; aside from any clipping, the output file has the exact same spatial extent and sample locations as the original file. If both translation and clipping are requested, then the clipping is applied after the translation.

-q

Quiet operation -- don't print informational messages.

-resample xstep ystep zstep <0|1|3>

Resample grid using specified step sizes. Each step size must exactly divide the grid extent in the corresponding direction, after any clipping. (That is, the export mesh consists of full cells only.) The last argument specifies the polynomial interpolation order: 0 for nearest value, 1 for trilinear interpolation, or 3 for fitting with tricubic Catmull-Rom splines. This control is only available for input files having a rectangular grid structure. Default is no resampling.

-rpertran rxoff ryoff rzoff

Similar to -pertran, except the offsets (rxoff, ryoff, rzoff) are interpreted as offsets in the range [0, 1] taken relative to the spatial extents of the x, y, and z coordinates. For example, if xmax - xmin = 500e-9, then an rxoff value of 0.1 is equivalent to an xoff value of 50e-9.

-subsample period

Reduce point density in output by subsampling input with specified period along x, y, and z axes. For example, if period is 2, then the output will have only 1/8th as many points as the input. This control is only available for input files having a rectangular grid structure. Default value is 1, i.e., no subsampling.

infile

Name of input file to process. Must be one of the recognized formats, OVF 0.0, OVF 1.0, OVF 2.0, or VIO. If no file is specified, reads from stdin.

outfile

Name of output file. If no file is specified, writes to stdout.

The -clip option is useful when one needs to do analysis on a small piece of a large simulation. The -info option is helpful here to discover the extents of the original mesh. The -clip option can also be used with -resample to enlarge the mesh.

The -flip option can be used to align different simulations to the same orientation. It can also be used to change a file into its mirror image; for example, ``-flip -x:y:z'' reflects the mesh through the yz-plane.

If multiple operations are specified, then the operation order is clip, resample, subsample, flip, and translate.

The -format text and -grid irreg options are handy for preparing files for import into non-OOMMF applications, since all non-data lines are readily identified by a leading ``#,'' and each data line is a 6-tuple consisting of the node location and vector value. Pay attention, however, to the scaling of the vector value as specified by ``# valueunit'' and ``# valuemultiplier'' header lines.

For output format details, see the OVF file description.

Known Bugs
If the input file contains an explicit boundary polygon (cf. the boundary entry in the Segment Header block subsection of the OVF file description) then the output file will also contain an explicit boundary polygon. If clipping is active, then the output boundary polygon is formed by moving the vertices from the input boundary polygon as necessary to bring them into the clipping region. This is arguably not correct, in particular for boundary edges that don't run parallel to a coordinate axis.

OOMMF Documentation Team
May 11, 2021