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Reference Guide
FITS_tutorial8.C File Reference

Detailed Description

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Open a FITS file with columns containing variable-length arrays.

ABOUT THE DATA: To illustrate such a case we use a Redistribution Matrix File (RMF) conform with the HEASARC OGIP specifications OGIP definition https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/spectra/ogip_92_007/ogip_92_007.html RMF defintion https://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_92_002/cal_gen_92_002.html#tth_sEc3.1

Variable-length arrays are used to return the non-null row elements of a sparse matrix containing the probability of detecting a photon of a given energy at a given detector channel.

The test data file, rmf.fits, is taken from the test data of the sherpa X-ray analysis tools https://cxc.harvard.edu/sherpa/ the original file is available under the repository https://github.com/sherpa/sherpa-test-data

void FITS_tutorial8()
// let us read the first header data unit, opening the file with a FITS viewer
// we see that the following cells contain variable-length arrays with values
// row 215 column "F_CHAN": (1, 68)
// row 215 column "N_CHAN": (66, 130)
// row 215 column "MATRIX" : (5.8425176E-6, 7.290097E-6, 8.188037E-6, 9.157882E-6, 1.018355E-5, ..)
TString dir = gROOT->GetTutorialDir();
TFITSHDU* hdu = new TFITSHDU(dir + "/fitsio/rmf.fits", 1);
int rownum = 214; // FITS tables are indexed starting from 1
TString colname1 = "F_CHAN";
TString colname2 = "N_CHAN";
TString colname3 = "MATRIX";
printf("reading in row %d, column %s \n", rownum+1, colname1.Data());
TArrayD *arr1 = hdu->GetTabVarLengthVectorCell(rownum, colname1);
printf("(%f, %f) \n", arr1->At(0), arr1->At(1));
printf("reading in row %d, column %s \n", rownum+1, colname2.Data());
TArrayD *arr2 = hdu->GetTabVarLengthVectorCell(rownum, colname2);
printf("(%f, %f) \n", arr2->At(0), arr2->At(1));
// printing only the first 5 values in the array
printf("reading in row %d, column %s \n", rownum+1, colname3.Data());
TArrayD *arr3 = hdu->GetTabVarLengthVectorCell(rownum, colname3);
printf("(%e, %e, %e, %e, %e, ...) \n", arr3->At(0), arr3->At(1), arr3->At(2), arr3->At(3), arr3->At(4));
reading in row 215, column F_CHAN
(1.000000, 68.000000)
reading in row 215, column N_CHAN
(66.000000, 130.000000)
reading in row 215, column MATRIX
(5.842518e-06, 7.290097e-06, 8.188037e-06, 9.157882e-06, 1.018355e-05, ...)
Cosimo Nigro

Definition in file FITS_tutorial8.C.

Double_t At(Int_t i) const
Definition: TArrayD.h:79
const char * Data() const
Definition: TString.h:369
Definition: TString.h:136
TArrayD * GetTabVarLengthVectorCell(Int_t rownum, Int_t colnum)
Get the variable-length array contained in a cell given by (row>=0, column name)
Definition: TFITS.cxx:1583
Definition: TFITS.h:35
Definition: TArrayD.h:27
#define gROOT
Definition: TROOT.h:406