eps1_texto.f:
277 * Calculate the pixel size conversion factor
278 SIZECONV = 1.0
279 IF (PSIZE.GT.0.0) THEN
280 * Display FWHM, rather than sigma
281 SIZECONV = SIZECONV * 2*SQRT(LOG(2.0))
282 ENDIF
283 IF (ABS(PSIZE).GE.1E-6) THEN
284 * Display in units of arcsec, rather than pixels
285 SIZECONV = SIZECONV * ABS(PSIZE)
286 END IF
Now, am I losing my mind here? I thought that FWHM as defined as
FWHM = sigma * sqrt(8ln2)
= sigma * 2 * sqrt(2ln2)
whereas the above uses
= sigma * 2 * sqrt(ln2)
To investigate further:
- ran gaufit on my mars image: FWHM = 11 x 13 arcsec
- wrote out model
- fitted that with PSF FWHM = 16.2 arcsec
- 16.2 / sqrt(2) = 11.45
so, um, only broken since 1997 then....
--
Tim Jenness
JAC software
http://www.jach.hawaii.edu/~timj
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