MOPEX User's Guide - IRSA

MOPEX User’s Guide
This module performs a projection of input images onto a 2D plane defined by the FIF table,
and an interpolation (see §8.4) of the input pixel values to the output array of pixels of the
user-defined pixel size. It corrects for the optical distortion in the input images, using the
WCS distortion parameters in the input FITS headers. The process is intended to accept
images measuring surface brightness (MJy/sr or microJy/arcsec 2 ) and to yield images in the
same units, but it is not restricted to this. If the input FITS header does not contain an allowed
string specifying units of MJy/sr or microJy/arcsec 2 , then it will assume the input units are
counts.
INPUT
INTERP METHOD: Four interpolation options are available:
1. Default: Each output pixel is a linear weighted sum of input pixels with weights equal
to the area overlap with the output pixel. The optional parameter is Fine Res (int). The
input pixel can be sub-divided with sub-pixel sizes of Input Pixel Size / Fine Res before
projecting onto the output array; a typical value might be 2. The value of each sub-pixel
is a linear interpolation of the input pixels with weights determined by the area overlap
with a pixel the same size as the original but centered on the sub-pixel. So it's a
convolution. The default value of 0 means no sub-dividing. We strongly advise setting
Fine Res = 0 as the Fine Res option is not fully implemented in the presence of bad
pixe ls.
2. Drizzle: Each input pixel is shrunk Drizzle Factor (float) times its origina l size along
each axis, e.g. 0.5. The value of the shrunken pixel is the same as the original pixel. The
shrunken pixels are then projected onto the output pixels with their values distributed into
output pixels according to area overlap. Note: When using Drizzle and creating RMasks
from the data, several of the mosaicking steps are run twice. First, a normal (Default)
interpolation is carried out so that MOPEX can run the outlier rejection scheme for the
original pixels. Once the outlier rejection masks (RMasks) have been created, MOPEX
returns to the Mosaic Interpolate module and re-runs the interpolation with the Drizzle
algorithm, masking out pixels flagged in the RMasks. When using this option, do not
include the Mosaic Reinterpolate Module in the processing flow.
3. Grid: This method is intended to create a crude first-look mosaic quickly. Each input
pixel is filled with Grid Ratio (int) squared grid points. Each grid point is assigned the
value of the pixel it belongs to. Each grid point is projected onto the output frame and the
flux associated with the grid point is added to the output image pixel into which the grid
point was projected. You may not run the Mosaic Reinterpolate module with this option.
Mosaicking (mosaic.pl) 65
Mosaic Modules