| CDF question [message #5405] |
Wed, 27 December 1995 00:00  |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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Please excuse me if this is a little outside the scope of this newsgroup, but I
couldn't find one specifically for Common Data Format.
I'm reading some FITS binary table files that were converted from CDF format.
The original CDF files have descriptions such as
!----------------------------------------------------------- --
! Variable Data Number Record Dim
! Name Type Elements Variance Variance
! ------- ---- -------- -------- --------
"LAT_SPACE" CDF_REAL8 1 T F
! Attribute Data Value
! Name Type
!----------- ----- ------
"FIELDNAM" CDF_CHAR { "Heliographic Lat of the Craft" }
"VALIDMIN" CDF_REAL8 { -1.570796327 }
"VALIDMAX" CDF_REAL8 { 1.570796327 }
"SCALEMIN" CDF_REAL8 { -1.570796327 }
"SCALEMAX" CDF_REAL8 { 1.570796327 }
"LABLAXIS" CDF_CHAR { "Helio Lat" }
"UNITS" CDF_CHAR { "rad" }
"FORMAT" CDF_CHAR { "F7.3" }
"DEPEND_0" CDF_CHAR { "Epoch" }
"FILLVAL" CDF_REAL8 { -1.0E31 }
"VAR_TYPE" CDF_CHAR { "data" }
"DICT_KEY" CDF_CHAR { " " }.
It appears that the data in the FITS binary table file has the same resolution
as that given in the FORMAT statement, rather than the full resolution of the
Real*8 data type. In the above example, the numbers are quantized to 0.001
radians, even though the double precision numbers are theoretically much more
precise than this.
I'm not very familiar with CDF, so I have some simple questions:
1. Are all CDF files written out to the resolution given by the FORMAT
statement? Or is there a mode of writing CDF files that automatically
applies this quantization?
2. If not, is it possible that the process of reading the CDF file
unintentionally quantized the values? In other words, is there a mode of
reading CDF files that automatically applies this quantization?
3. Failing the above two possibilities, is it standard practice for CDF files
written by some of the groups here at Goddard to write out data to a
quantization given by the FORMAT specification.
Please excuse these possibly naive questions.
Thank you,
Bill Thompson
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