Round off problem in hedit

Philip Massey wrote on Jun 28, 2006

Hi, Mike et al---

I have an image that has astrometric parameters that were added via tfinder,
specifically numbers like:

CRVAL1 = 0.349583333333341
CRVAL2 = -15.295722222222
CRPIX1 = 1079.04400338829
CRPIX2 = 1242.12076751727
CD1_1 = 1.11412107413711E-4
CD1_2 = 8.17548433351806E-8
CD2_1 = 1.04285743207307E-7
CD2_2 = 1.11512925113402E-4

I'd like to transfer these to a different image, but when I go to hedit them
as
hedit otherimage.fits CD1_1 1.11412107413711E-4 add+ ver- show+
what I instead get is:
add test.fits,CD1_1 = 1.114121E-4

Is there someway I can add these values and keep all the digits?
Alternatively, is there some way I can add specific keywords from one
image to another?

thanks,
phil

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Mike Fitzpatrick wrote on Jun 28, 2006

Hi Phil,

This has been reported before but apparently never changed. HEDIT only implements a real-valued keyword addition and not double-precision, so the roundoff is occurring. One workaround is to use the ASTHEDIT task instead, e.g.

as> asthedit pix ""
asthedit> dummy = 1.23456789012345
asthedit> quit
as> hselect pix dummy yes
1.23456789012345

This task does use double-precision, see the help page for details. You might also look at HFIX as a way to run any sort of command/host script on the header file so you could simply treat the header as a text file an update all the keywords in bulk. It might not apply directly here, but when I first read your message I was thinking the WCSCOPY task would help as well.

Cheers,
-Mike

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Last post on Jun 28, 2006