how can i read a use a fits file?

1) reads spectrum array from this file;

2) reads keywords from the header of this file and using these keywords computes the wavelength array according to the formula I provided;

3) plots on the screen spectrum vs. wavelength for the wavelength

file contains the header and a single array (spectrum). Wavelengths can be calculated from the keywords NAXIS1, CDELT1, CRVAL1 in the header:

Wavelength = exp( array[0:NAXIS1-1] * CDELT1+CRVAL1 )

"array[0:NAXIS1-1]" is an integer array from 0 to NAXIS1-1 with a step of 1.

Answer 1

[Asvin Kumar]

I think what you're looking for are the fitsread and fitsinfo functions.

There are examples in the doc pages for the both the functions. Here's another: https://www.mathworks.com/help/matlab/import_export/importing-flexible-image-transport-system-fits-files.html

As mentioned in the fitsinfo doc page, the keywords NAXIS1, CDELT1, CRVAL1 which you're looking for are under the Keywords property of the PrimaryData structure in the returned info structure.

Here's an example adapted from the one linked above:

info = fitsinfo('tst0012.fits')

info =

struct with fields:

Filename: '/local-ssd/asvenkat/MATLAB/toolbox/matlab/demos/tst0012.fits'

FileModDate: '13-Mar-2001 05:07:46'

FileSize: 109440

Contents: {1×5 cell}

PrimaryData: [1×1 struct]

BinaryTable: [1×1 struct]

Unknown: [1×1 struct]

Image: [1×1 struct]

AsciiTable: [1×1 struct]

info.PrimaryData.Keywords

ans =

25×3 cell array

{'SIMPLE' } {'T' } {' Standard FITS file …'}

{'BITPIX' } {[ -32]} {' No. of bits per pixel …'}

{'NAXIS' } {[ 2]} {' No. of axes in matrix …'}

{'NAXIS1' } {[ 102]} {' No. of pixels in X …'}

{'NAXIS2' } {[ 109]} {' No. of pixels in Y …'}

{'EXTEND' } {'T' } {' There may be FITS extensions …'}

{'BLOCKED'} {'T' } {' The file may be blocked …'}

{0×0 char } {0×0 char } {0×0 char }

{'CDELT1' } {[ 3.1000]} {' Coordinate increment …'}

{'CRVAL1' } {[ 1.2991e+03]} {' Coordinate of reference pixel …'}

{'CRPIX1' } {[ 12.3000]} {' Reference pixel in X …'}

{0×0 char } {0×0 char } {0×0 char }

{'CDELT2' } {[ -0.1700]} {' Coordinate increment …'}

{'CRVAL2' } {[ -102.4000]} {' Coordinate of reference pixel …'}

{'CRPIX2' } {[ -2.0318e+03]} {' Reference pixel in Y …'}

{0×0 char } {0×0 char } {0×0 char }

{'OBJECT' } {'Wave 32-bit FP'} {' Name of image …'}

{'ORIGIN' } {'ESO' } {' File was prepared at ESO-Garching …'}

{'DATE' } {'20/08/92' } {' Creation data of this file …'}

{0×0 char } {0×0 char } {0×0 char }

{'COMMENT'} {0×0 char } {' This test file was created by P.Grosbol, ES…'}

{0×0 char } {0×0 char } {0×0 char }

{'COMMENT'} {0×0 char } {' Simple 32-bit FP sine wave pattern for test…'}

{0×0 char } {0×0 char } {0×0 char }

{'END' } {0×0 char } {0×0 char }