Code examples for the NGTS wiki page

catalogue_hdu_example.py

'''
Read in the catalogue RA and DEC positions and plot as a scatter plot
'''
 
from astropy.io import fits
import matplotlib.pyplot as plt
 
with fits.open("example.fits") as hdulist:
    catalogue = hdulist['catalogue'].data
    ra = catalogue['ra']
    dec = catalogue['dec']
 
plt.plot(ra, dec, 'k.')
plt.show()

extract_fwhm.py

'''
Read in the FWHM as a function of time from the imagelist hdu, and plot the time series
'''
from astropy.io import fits
import matplotlib.pyplot as plt

with fits.open("example.fits") as hdulist:
    imagelist = hdulist['imagelist'].data
    mjd = imagelist['tmid']
    fwhm = imagelist_hdu['fwhm']
    
mjd0 = int(mjd.min())
mjd -= mjd0

plt.plot(mjd, fwhm, 'k.')
plt.show()

image_hdu_example.c

#include <stdio.h>
#include <fitsio.h>
 
void check_fits_error(int status);
 
int main() {
    fitsfile *fptr;
    int status = 0, i = 0;
    long naxes[] = {0, 0};
    long napertures = 0, nimages = 0;
    float *image_data = NULL;
    long chosen_aperture = 100;     // Which aperture to extract
    long fpixel[] = {chosen_aperture + 1, 1};
 
    fits_open_file(&fptr, "example.fits", READONLY, &status);
    check_fits_error(status);
 
    // Move to the flux hdu
    fits_movnam_hdu(fptr, IMAGE_HDU, "flux", 0, &status);
    check_fits_error(status);
 
    // Get the image dimensions
    fits_get_img_size(fptr, 2, naxes, &status);
    check_fits_error(status);
 
    nimages = naxes[0];
    napertures = naxes[1];
 
    printf("Found %ld images and %ld apertures\n", nimages, napertures);
 
    // Read the flux lightcurve
    image_data = malloc(nimages * sizeof(float));
    fits_read_pix(fptr, TFLOAT, fpixel, nimages, NULL, image_data, NULL, &status);
    check_fits_error(status);
 
    for (i=0; i<nimages; i++) {
        printf("%f\n", image_data[i]);
    }
 
    /* And so on reading the other image hdus
     * ...
     */
 
    // Cleanup
    free(image_data);
    fits_close_file(fptr, &status);
    check_fits_error(status);
 
    return 0;
}
 
void check_fits_error(int status) {
    if (status) {
        fits_report_error(stderr, status);
        exit(status);
    }
}

image_hdu_example.py

'''
This code reads in the example fits file, extracts the chosen aperture index from 
the file and plots the lightcurve with errors.

The method below avoids reading in the full (potentially large) images into memory.
'''
from astropy.io import fits
import matplotlib.pyplot as plt

chosen_aperture_index = 100
s = slice(chosen_aperture_index, chosen_aperture_index + 1)

with fits.open("example.fits") as hdulist:
  hjd = hdulist['hjd'].data[s].flatten()
  flux = hdulist['flux'].data[s].flatten()
  fluxerr = hdulist['fluxerr'].data[s].flatten()

plt.errorbar(hjd, flux, fluxerr, ls='None', marker='.')
plt.show()