[Kst] [Bug 123699] fails to create INDEX from .fits file binary extention

Theodore Kisner tskisner.public at gmail.com
Sat Jun 17 06:25:28 CEST 2006

I sent this to the bug tracking system, but it hasn't shown up for a couple 
hours, so I have revised it a bit and sent it to the list...

On Friday 16 June 2006 14:22, netterfield at astro.utoronto.ca wrote:
| The problem is significant: A fits file has no concept of frames.  But kst
| wants to know how many frames a data source has so it knows what it can ask
| for.  It must be that now the data source generates NF from the size of the
| first data object in the file, so it would be expected that it would also
| generate INDEX from the first data object in the file.  Anything else, and
| we have bigger fish to fry (like over or under reading fields).

Isn't this is the *whole point* of specifying the desired field in the call to 
KstDataSource::frameCount(field)?  In general, fields within a datasource are 
not required to have the same frame count.  If a specific datasource wants to 
require that (e.g. dirfile), then fine, but it is not a general requirement.

| I suggest that for the short term, we generate INDEX and NF from the first
| data object in the file.

why?  why can't the datasource return as many index samples as requested?  The 
datasource should query each "real" field to determine its length.  If we 
cannot support this scenario, then (in my opinion) our datasource model is 
fundamentally broken.  We should never use the length of the INDEX field to 
determine the number of samples/frames.  

The index field is just a dummy placeholder when we want to plot data vectors 
versus sample number.  At some level, the INDEX functionality should be built 
into the basecurve so we don't have to deal with it over and over again in 
the datasources.

| For the long term, I think we need to some how break a fits file into
| sub-data sources each with equal sized fields as Piolib apparently does.

This is not the method I'm using in libfitstools and the fitsgeneral 
datasource.  I think it is better to have the fitsgeneral datasource present 
a fieldlist/matrixlist of all data in a given FITS file.


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