Content-type: text/html Manpage of regrid


Section: User Commands (1)
Index Return to Main Contents


regrid - Regrid an image dataset  




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,
  * 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.  


The input image name. No default.
The output image name. No default.
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.
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.
If "tin" is unset, this gives the reference value, reference pixel, pixel increment, and number of pixels for the axes selected by keyword "axes" of the output image, respectively.

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.

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 or
            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 between B1950 and
Output map projection. Possible values are "sin", "tan", "arc", "ncp", "car" or "gls". Note that the NCP projection has a singularity at the equator. The default is not to change the output projection.
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.
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.

grid.for,v 1.4 2011/06/27 21:30:32 pteuben Exp $




This document was created by man2html, using the manual pages.
Time: 18:35:38 GMT, July 05, 2011