Thread: Cfitsio?

Hi All,
I was wondering if anyone had any experience with CFITSIO. I have a FITS file with random grouped data. I would like to extract this data and, among other things, put it into a more accessible format.

I have been trying to use the command: fits_read_grppar_[flt] (fitsfile *fptr, long group, long firstelem, long nelements, > DTYPE *array, int *status ) without much success. I think I am most confused about the "long group" input. The documentation for this command is fairly scarce, and I do not know if the data is even in a group, or what the default input would be.

The reference for the above command is here. Thanks,

Dillon

I think you'll have to be more specific about your question. Syntax? Semantics? What?

Ok, so, I was able to figure it out. Thanks for all your help, tabstop, and thanks for warning me about potential problems QuantumPete. For anyone who is interested, I'll explain what I found out below.

A FITS file with random group data will have a NAXIS1 parameter of 0, i.e. the primary data unit in the primary Header-Data Unit appears to have no rows. This makes it difficult to view with standard fits viewer software (I never found a program that could, although fv was the best).

Also in the primary header is the number of groups in the random grouped data. There is a keyword, GROUPS, which tells you how many groups that data is stored in. The "long groups" that I was confused about primarily, is then just the number of any particular group. If you need to extract all of the data contained in the file, you can simply loop through the groups, and read the data into whatever you need. The nelements is then the number of entries in the group, which you can get by multiplying the NAXIS2 and NAXIS3 keywords together. The DTYPE *array is where you are extracting the data into (with DTYPE being a generic keyword which is replaced with whatever data type the group contains). The status variable is an error-check which is set to zero at the beginning of any script utilizing cfitsio. If anything goes wrong with a particular routine, status is then set to a non-zero value, which helps debugging.

So, using what I found, one simply just supply a pointer to the fits file, and the group number, and the random grouped data will be extracted. Let me know if you want to know anymore, but it kind of resolved to be more of a FITS problem than a problem with C. Thanks again for all of your help though.

Dillon