[ Basic Info | References | User Guide ]
Basic Information on regrid
Task: regrid
Purpose: Regrid an image dataset
Categories: map analysis
REGRID regrids an image by interpolating. The output coordinate
system can be specified by a template image or by
axis descriptors. Blanked input pixels are excluded from the
interpolation. Regridding of any combination of the first three
axes of an image is supported.
REGRID correctly handles conversion
* Between different projection geometries (e.g. SIN,NCP,TAN etc).
* Between equatorial and galactic coordinates.
* From a B1950 input to J2000 output and visa versa,
as well as B1950 to B1950, and J2000 to J2000.
* Between radio/optical velocity definitions and LSR/barycentric
velocity rest frames.
Nearest neighbour `interpolation' is used for axes smaller in size
that 5 pixels. Otherwise an cubic interpolation is used.
Key: in
The input image name. No default.
Key: out
The output image name. No default.
Key: axes
Specify axes to regrid. For example, axes=1,2 will regrid
axes 1 and 2, or axes=2,3 will regrid axes 2 and 3.
The default is all axes.
Key: tin
Input template image. The axis descriptors of the regridded
image, for those axes specified by keyword "axis", are those
of the template image.
If neither a template nor a set of "descriptors" (see below) are
given, the input is used as an initial template.
Key: desc
If "tin" is unset, then this gives the reference value, reference
pixel, pixel increment, and number of pixels for the axes
selected by keyword "axes" of the output image, in the same order
that they are given.
Note that for RA/DEC axes, the reference values are in radians, and
the increments are in radians on
the sky. Thus, dRA = dX / cos(dec) and dDEC = dY where you
specify dX and dY.
Defaults are no axis descriptors.
Key: options
Extra processing options. Several can be given, separated by commas.
Only the minimum characters to avoid ambiguity is needed.
noscale Produce a cube where the RA/DEC cell size does not scale
with frequency/velocity.
offset The coordinate system described by the template or
descriptors is modified (shift and expansion/contraction)
by an integral number of pixels so that it completely
encloses the input.
nearest Use nearest neighbour interpolation rather than the
default higher order interpolation scheme.
galeqsw Switch the output coordinate system between equatorial
and galactic.
equisw Switch the equinox of the output bwtween B1950 and J2000.
Note that REGRID always produces galactic coordinates in
the B1950 frame.
Key: project
This allows the projection of the output to be changed. Possible
values are "sin", "tan", "arc", "ncp", "car" or "gls". Note that
the NCP projection has a singularity at the equator. The default is
to not change the output projection.
Key: rotate
Set the rotation between the sky and the image to be this angle,
in degrees. The positive value of the angle gives an eastward
rotation of the sky grid relative to the pixel grid.
The default is not to change the rotation from that of
the template, or to have no rotation when there is no template.
Key: tol
Interpolation tolerance. Tolerate an error of as much as "tol" in
converting pixel locations in the input to the output. The default is
0.05. It must be less that 0.5.