AstroPy - findlimb.py

Description

This program looks for the bright limb of a planet in the rows of a raw image. It depends upon the saturated crescent having negative values. This program is used in the alignment programs which follow.

Usage

findlimb.py fits-file [thresh dir interval0 interval1 min_count]

   'thresh' is the fraction (0.0 to 1.0) of the row max that a peak must be.
   Default = 0.75.

   'dir' is the orientation of the bright limb. 0 = sun to the right, 1 = sun to the left.
   Default = 0.

   'interval0' is the number of pixels to the left of each peak.
   'interval1' is the number of pixels to the right of each peak.
   Default = [50, 5].

   'min_count' is the minimum number of negative values which must be in the crescent side of the peak.
   Default = 5.

The program looks for peaks in each interval = [peak-interval0, peak+interval1] that are >= thresh * row.max(), and such that there are no negative values in the sun side of the interval, and >= min_count negatives in the planet (crescent) side. The program contains a function which can be called from other programs:

findLimbInRow(row, thresh=0.75, dir=0, interval=(50, 5), minCount=5)
   row is a 1d numpy array.

Examples

This program works reasonably well on most raw images having the sun on either side:

> findlimb.py 090807/raw/im1648.a.fits 0.75 1 5 50 5
Row   0: []
Row  32: []
Row  64: []
Row  96: []
Row 128: [74]
Row 160: [59]
Row 192: [53]
Row 224: [51]
Row 256: [51]
Row 288: [59]
Row 320: [69]
Row 352: [91]
Row 384: [118]
Row 416: [168]
Row 448: []
Row 480: []

To use on an image with the other orientation (sun at right), set dir = 0 and reverse the values of interval0 and interval1 (or use the default values):

> findlimb.py 072407/raw/im0215.a.fits 0.75 0 50 5 5
Row   0: []
Row  32: []
Row  64: []
Row  96: [434]
Row 128: [467]
Row 160: [487]
Row 192: [501]
Row 224: [504]
Row 256: [505]
Row 288: [503]
Row 320: [498]
Row 352: [486]
Row 384: []
Row 416: []
Row 448: []
Row 480: []