<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>Actually, NAXIS2 = 0 in the primary array of the UV visibility data files, so there is no primary data array. The real data is in the following binary table. The weird value for NAXIS1 was apparently deliberately chosen to serve as a signal to the processing software that this file contains visibility data. </div><div><br>On Jun 2, 2016, at 9:45 AM, Arnold Rots <<a href="mailto:arots@cfa.harvard.edu">arots@cfa.harvard.edu</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><div dir="ltr"><div><div><div><div><div><div>Let me make sure I get this right:<br></div>I suspect you mean that the second axis is one pixel long.<br></div>If it were zero pixels long, there would be no pixels in the image at all.<br></div>I note that this mechanism (single-pixel axes) has been used extensively<br></div>in radio astronomy to specify the polarization and frequency of 2-D images.<br><br></div>Cheers,<br><br></div> - Arnold<br></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr">-------------------------------------------------------------------------------------------------------------<br>Arnold H. Rots Chandra X-ray Science Center<br>Smithsonian Astrophysical Observatory tel: +1 617 496 7701<br>60 Garden Street, MS 67 fax: +1 617 495 7356<br>Cambridge, MA 02138 <a href="mailto:arots@cfa.harvard.edu" target="_blank">arots@cfa.harvard.edu</a><br>USA <a href="http://hea-www.harvard.edu/~arots/" target="_blank">http://hea-www.harvard.edu/~arots/</a><br>--------------------------------------------------------------------------------------------------------------<br><br></div></div></div>
<br><div class="gmail_quote">On Thu, Jun 2, 2016 at 1:04 AM, William Pence <span dir="ltr"><<a href="mailto:William.Pence@nasa.gov" target="_blank">William.Pence@nasa.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p><tt>On 6/1/2016 11:14 AM, Demitri Muna wrote:
</tt></p><blockquote type="cite"><tt>
There is a significant difference between documenting use of
the FITS format and incorporating it into the standard. As an
example, I recently came across UV data, which immediately
crashed my FITS viewer, and then this in the AIPS File Format
Memo:
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<p><span style="font-size:10.000000pt;font-family:'CMR10'">In the UV-tables
form, the visibility data are written as a FITS
binary table, normally placed after the other
table extensions. The primary HDU has an </span><span style="font-size:10.000000pt;font-family:'CMSY10'">AIPS </span><span style="font-size:10.000000pt;font-family:'CMR10'">conventional form meant
primarily to be so odd as to
act as a reliable identifier. The primary HDU
asserts that the primary data has two axes, the
first of which
has 777777701 values while the second has zero
values. This is su</span><span style="font-size:10.000000pt;font-family:'CMR10'">ffi</span><span style="font-size:10.000000pt;font-family:'CMR10'">cient to tell all FITS readers
that the
primary data set is not a random groups data set
and otherwise contains no data. </span></p>
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<div>This may be convention, but it's *lying*. I'm
sure that there are untold numbers of FITS files of UV data
that use this convention. Should it be part of the standard?
Absolutely not.</div>
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</tt><p></p>
</span><tt>It is legal for a FITS image to have one or more zero length
axes as well as other non-zero length axes, so these UV visibility
data do conform to the requirements of the FITS standard and are
not lying. One could say that these 2D images really are
777777701 pixels wide, but because they are 0 pixel high they are
hard to see. :-)<br>
</tt><tt><tt><span style="font-size:10.000000pt;font-family:'CMR10'"></span></tt><br>
-Bill<br>
<br>
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