The (2D)
four-point interpolation that is used in regridding
is based on the one in *cmhog/movie.src*, but includes correct interpolations
for points near the Y axis that need contributions from the phantom "mirror"
points (recall that the files are assumed to contain X>0 information only,
the X<0 plane is assumed from point symmetry around the origin).

It is also
possible to simply average the polar grid values into cartesian cells,
using the **pic=t** method, but this will generally result in variable amount
of smoothing and depending on the distribution of points in Rad-Phi can
cause moire patterns.

**in=***hdf_sds*- Input file (HDF SD). No default.
**out=***image*- Output file, in
*image(5NEMO)*format. **select=***frame_no*- Select which SDS from the file (1=first). See also
**zvar=**below. [Default:**1**]. **nx=***X_pixels*- Number of pixels in X. [Default:
**256**] **ny=***Y_pixels*- Number
of pixels in Y [Default:
**256**]. **xrange=***xmin:xmax*- Range in X [Default:
**-16:16**]. **yrange=***ymin:ymax*- Range in Y [Default:
**-16:16**]. **zvar=***grid_var*- Gridding variable. Normally left alone, unless certain allowed mathematical
expressions on the direct griddable variables (as defined by
**select=**) need to be overriden. Allowed are**vr**(select=1),**vt**(select=2),**den**(select=3),**vx**,**vy**,**vm**and**vp**. Note that**vm**and**vp**are special cases of a linear combination of**vx**,**vy***vm = (vx-vy)/sqrt(2)*and*vp = (vx+vy)/sqrt(2)*, just to get an idea of the velocity field under a "middle" position angle. Default: not used, select= is used. **pic=t|f**- Use the Particle In Cell method of gridding?
This method is similar, but not as sophisticated as
*snapgrid(1NEMO)*. The alternative, and also the default method, is 4-point interpolation from the corner cell in polar coordinates in which the cartesian cell center lies. [Default:**t**]. **mirror=t|f**- Mirror points? [Default:
**t**]. **symmetry=odd|even|automatic**- Override symmetry properties of the variable to be gridded. This option
is not used yet. See also
**mirror=** **it0=**- Shifts the values in theta by
**it0**pixels. This is equivalent by rotating the image counterclockwise by that many pixels. Useful for double bars and manually rotating the frame of reference (Maciejewski et al). [Default:**0**] **phi1=**- The first operation is a rotation. This angle (in radians) will be added to the angles. Do not ues for serious work, as it only applies to density fields. Default: 0
**scale2=**- The second operation is a scaling. All angles are multiplies by this number.
**phi3=**- The
third, and last, operation is a rotation again. This angle (in radians)
will be added to the angles after the previous two. It was added for convenience,
since in principle
**phi1**and scale2 can get you anywhere on the plane. The resulting formulae is:

Default: 0

hdfgrid hdf001 - select=3 nx=256 ny=256 xrange=-8:8 yrange=-8:8 |\ ccdmath - - "log(%1)" |\ ccdmath - - "ifeq(%1,0.0,$dmin,%1)" |\ ccdfits - tmp$$ fitstiff tmp$$ movie1.$i.tiff datamin=-1 datamax=2 lut=dsSeveral interesting peculiarities are to be noted: (1) ccdmath is called twice, because of a bug in combining the two;

25-May-95V1.0 Created for IAU157 moviePJT 12-dec-99V1.3 added it0= shifting arrays to fake a rotation, for WitoldPJT 27-aug-02V1.5 added mirror= to allow for full grid simulationsPJT 3-dec-04V2.0 increased MAXRANK to handle 2+1 dim input filesPJT 15-dec-04V2.1 added pic=, and documented the new phi1,scale2,phi3 transformationsPJT