MOPEX Online Manual
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Overlap Modules: Compute Overlap Correction
Output Directory Keyword: OVERLAP_CORR_DIR
Default Output Directory: <output_dir>/Overlap_Corr
Depends on: Input files; Mosaic Interpolate
Important Notes: Running this module does not automatically apply the overlap correction. In order to apply the correction and output the corrected BCDs, the trigger apply_overlap_correction must be set in the namelist (see Overlap Namelist Options).
PURPOSE
This module computes the correction needed to set the background of overlapping images to a constant value. Optionally, it applies the correction to the input BCD images and creates corrected images for input to the Mosaicker.
PARAMETER BLOCK
-
&COMPUTEOVRLAPCORRIN
TOP_THRESHOLD = 3,
BOTTOM_THRESHOLD = 3,
MIN_IMG_NUM = 4,
&END
INPUTS
TOP_THRESHOLD: (float) Number of sigma above the mean to detect outliers among the computed offsets.
BOTTOM_THRESHOLD: (float) Number of sigma below the mean to detect outliers among the computed offsets.
MIN_IMG_NUM: (int) Minimum number of overlapping images to perform outlier rejection.
OUTPUTS
Overlap Correction Table (offsets.tbl): A table of calculated offsets for each input DCE is the primary output of the Overlap flow.
Corrected Images (overlapCorrectoin_*.fits): If Apply Overlap Correction is selected, a new FITS stack is output, with the background-matching offsets applied.
These outputs are written to the Overlap_corr subdirectory.
DISCUSSION
The background matching algorithm calculates an offset to apply to each image in order to set their backgrounds to a constant value. After the initial calculation, the offsets are examined, and outliers are rejected, as long as the minimum number of images are present. The other inputs to this module control how much of an outlier an offset has to be in order to be rejected. A rejected outlier will not be used in determining the overall offset level for all frames, but will still be applied to the corresponding data frame to bring the background to the same offset as the other input frames.
The offsets and their uncertainties are written in the header of the corresponding output FITS files. The keywords are OVRLPDC and OVRLPDCD. They keyword OVRLPOUT is set to 1 if the offset was determined to be an outlier. A table, offset.tbl, is also created, containing the offsets and their uncertainties for all the files. The outliers column is used to indicate whether the offset in that row was determined to be an outlier. Below is a sample output table:
|Image_id| Offset | del_Offset | outliers |
| int | real | real | int |
1 0.13305403 0.00988516 1
2 0.09888604 0.00963296 0
3 0.01376509 0.00964912 0
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