Transcript Reading and Writing FITS Files

Reading and Writing FITS Files
General tools:
In IDL:
fits_info – Summarizes FITS file primary data and extensions
Example: fits_info, 'hsi_spectrum_20020421_004040.fits'
mrdfits – Reads an extension in a FITS file
Calling sequence: data = mrdfits(file, ext, header)
Example: data = mrdfits('hsi_spectrum_20020421_004040.fits‘, 0, header)
headfits – Reads header from an extension of a FITS file
Example: header = headfits('hsi_spectrum_20020421_004040.fits', exten=1)
mwrfits – Writes an extension in a FITS file
FITS object – Under construction
$SSW/gen/fits directory contains many IDL tools to read/write FITS files
Astronomy Library at GSFC documentation on SSW FITS I/O
FV tool from HEASARC at GSFC
Free software tool you can download
Graphical interface for examining FITS files easily
Allows for plotting of rows/columns in FITS files
IDL> fits_info,'hsi_spectrum_20020421_004040.fits
hsi_spectrum_20020421_004040.fits has 3 extensions
Primary header: 26 records
No data
Extension 1 -- 'RATE '
/
Header : 67 records
Binary Table ( 792 820 )
Extension 2 -- 'ENEBAND '
/Extension name
Header : 52 records
Binary Table ( 970 1 )
Extension 3 -- 'HESSI Spectral Object Parameters' /
Header : 300 records
Binary Table ( 173821 1 )
IDL> data = mrdfits('hsi_spectrum_20020421_004040.fits', 1, header)
MRDFITS: Binary table. 5 columns by 820 rows.
IDL> help,data
DATA
STRUCT
= -> <Anonymous> Array[820]
IDL> help,data,/st
** Structure <3c6dce0>, 5 tags, length=800, data length=792, refs=1:
RATE
FLOAT Array[97]
ERROR
FLOAT Array[97]
LIVETIME
FLOAT
0.910374
TIME
DOUBLE
52385.028
TIMEDEL
FLOAT
4.62963e-005
IDL> help, header
HEADER
STRING
IDL> prstr, header
= Array[67]
XTENSION= 'BINTABLE'
/Written by IDL: Mon Jul 12 10:42:49 2004
BITPIX =
8/
NAXIS =
2/
NAXIS1 =
792 /Number of bytes per row
NAXIS2 =
820 /Number of rows
PCOUNT =
0 /Random parameter count
GCOUNT =
1 /Group count
TFIELDS =
5 /Number of columns
COMMENT
COMMENT *** End of mandatory fields ***
COMMENT
DATE = '2004-07-12'
/
ORIGIN = 'HESSI '
/High Energy Solar Spectroscopic Imager
OBSERVER= 'unknown '
/Usually the name of the user who generated file
TELESCOP= 'HESSI '
/High Energy Solar Spectroscopic Imager
OBJECT = 'Sun '
/
DATE_OBS= '2002-04-21T00:40:40.000' /
DATE_END= '2002-04-21T01:35:20.000' /
GEOAREA =
356.310 /
DETUSED = 'SEGMENTS: 1F|2F|3F|4F|5F|6F|7F|8F|9F' /
SUMFLAG =
1 /Spectra summed over detectors
SUMCOINC=
0/
COINCIDE=
0 /Anti-coincident spectra
RESPFILE= 'hsi_srm_20020421_004040.fits' /
TIMESYS = 'MJD '
/
TIMEUNIT= 'd
'
/
MJDREF = '
'
/Undefined for HESSI.
TIMEZERI=
52385 /
TIMEZERF=
0.028240741 /
…
…
New FITS object
Use is similar to RHESSI objects
Use SET, GET, GETDATA to read FITS file
Under construction – basics are available now, more methods will be added
Example:
o = fitsread( filename = 'test_cube_small.fits' )
print, o->getstatus()
print, o-> getfield( extension = 1, 'cbe_det_eff$$avg' )
o->set, extension = 1
print, o->get( /extension )
print, o->getdata( /header )
data = o->getdata()
obj_destroy, o
RHESSI Spectrum FITS files
GUI:
In the Spectrum Widget, set up your parameters, press the ‘Write Output File’ Button. You’ll see this
widget:
CLI:
Create and set parameters in a spectrum object and call filewrite method. Options to filewrite are:
/buildsrm – If set, write an SRM file in addition to the spectrum file
/autoname – If set, autoname FITS files based on time of data
all_simplify = 0, 1, 2, or 3. Specifies type of SRM to calculate:
0 = full matrix
1 = off diagonal terms are an approximation
2 = diagonal terms only
3 = diagonal terms only and all are set to 1
srmfile = name of SRM FITS file to write
specfile = name of spectrum FITS file to write
Example: o -> filewrite, /buildsrm, /autoname, all_simplify=2
RHESSI Spectrum FITS Files (cont)
Spectrum and SRM FITS files are used as input to OSPEX and SPEX to proceed with spectroscopy analysis
Detectors must be summed (sum_flag set to 1 in object) in FITS files for use in OSPEX, SPEX
To analyze separate detectors, write a separate file for each detector (for now)
Energy bins must be defined in terms of keV, not channel numbers, for use in OSPEX, SPEX
SRM file will contain SRM for all attenuator states during spectrum time interval
OSPEX will automatically choose the correct one for each fit time interval
SPEX will only use first one (corresponding to attenuator state at start of spectrum time interval)
Use hsi_break_srm to break up the SRM file into separate SRM files for each attenuator state for use in
SPEX.
No mechanism for using a FITS file to create a spectrum object currently
IDL> fits_info,'hsi_srm_20020421_004040.fits'
hsi_srm_20020421_004040.fits has 5 extensions
Primary header: 12 records
No data
Extension 1 -- 'SPECRESP MATRIX' /Extension name
Header : 61 records
Binary Table ( 402 107 )
Extension 2 -- 'EBOUNDS '
/Extension name
Header : 49 records
Binary Table ( 1164 1 )
Extension 3 -- 'SRM Object Parameters' /
Header : 95 records
Binary Table ( 2093 1 )
Extension 4 -- 'SPECRESP MATRIX' /Extension name
Header : 61 records
Binary Table ( 402 107 )
Extension 5 -- 'SPECRESP MATRIX' /Extension name
Header : 61 records
Binary Table ( 402 107 )
IDL> srm1 = mrdfits('hsi_srm_20020421_004040.fits', 1, header1)
MRDFITS: Binary table. 6 columns by 107 rows.
IDL> help,srm1
SRM
STRUCT
= -> <Anonymous> Array[107]
IDL> help,srm1,/st
** Structure <3247e80>, 6 tags, length=404, data length=402, refs=1:
ENERG_LO
FLOAT
3.00000
ENERG_HI
FLOAT
4.00000
N_GRP
INT
1
F_CHAN
INT
0
N_CHAN
INT
97
MATRIX
FLOAT Array[97]
IDL> print,fxpar(header1, 'FILTER')
0
IDL> srm4 = mrdfits('hsi_srm_20020421_004040.fits', 4, header4)
MRDFITS: Binary table. 6 columns by 107 rows.
IDL> print,fxpar(header4, 'FILTER')
1
IDL> srm5 = mrdfits('hsi_srm_20020421_004040.fits', 5, header5)
MRDFITS: Binary table. 6 columns by 107 rows.
IDL> print,fxpar(header5, 'FILTER')
3
RHESSI Image FITS files with GUI
GUI:
Writing Image FITS file
• In the Image widget, select option to create FITS file when generating image
• Select any RHESSI image panel in the GUI, and click File /Export Data / Write Fits file
Reading Image FITS file
• Click File / Import FITS file
RHESSI Image FITS files with CLI
Writing Image FITS Files
Create an image object, set parameters, and call fitswrite method
Example: o -> fitswrite, fitsfile=‘xxx.fits’
Currently for single images only, image cube requires use of hsi_multi_image object
Reading Image FITS Files
hsi_image_fitsread – returns image data, object, info/control parameters, plots images. Many options.
Example: image = hsi_image_fitsread()
hsi_fits2map – reads image file and creates an array of map structures
Example: hsi_fits2map, fitsfile, map
However:
• New and improved image object software will be online very soon
• New hsi_image will handle single image and image cube
• New hsi_image will read data either from telemetry files or from an image FITS file
OSPEX FITS Files
OSPEX stores results of analysis in FITS files
OSPEX GUI:
•Click File / Save Fit Results / In FITS file to write FITS file
•Click File / Import Fit Results to read FITS file
OSPEX CLI:
•Use savefit method to write FITS file
Example: ospex_obj -> savefit
•Use restorefit method to restore import results in FITS file into OSPEX object
Example: ospex_obj -> restorefit
•Use spex_read_fit_results to read FITS file into structure
Example: structure = spex_read_fit_results(file)