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

Nicolas Brisset nicolas.brisset at eurocopter.com
Mon Jun 19 15:36:32 CEST 2006

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------- Additional Comments From nicolas.brisset eurocopter com  2006-06-19 15:36 -------

On Friday 16 June 2006 21:52, Barth Netterfield wrote:
| The reason to have a single length per field is to handle asyronously 
| arriving real time data in count from end mode (ie, the #1 requirement 
| for kst), to make sure that the X vectors and the Y vectors stay synced.
| Because of this, in fact, currently, fields within a data source are 
| required to have the same frame count.  NF is a property of a datasource.

Yes, we've beaten on this issue a ton for dirfiles, but it seems to me that synchronicity is a datasource-dependent feature which doesn't make sense for some datasources. 

| Perhaps the best solution is to let the data source decide - it can 
| know which is appropriate.

I thought this was why we had the "field" argument to the frameCount function?  
The datasource can choose whether to use it or ignore it.

| -kst learns to read NF on a per field basis, not a per data source basis.

I am obviously confused- doesn't it already do this???  As far as I can tell from grep'ing through the sources, every call to KstDataSource::frameCount includes the field parameter- and thus the datasource can take advantage of it.  

What am I missing?  Obviously the dirfile source can ignore the field parameter, but other datasources can use it already.

| -Data sources that need to are responsible to make sure that NF is the 
| same for all fields.  Data sources that don't need to don't (eg: 
| dirfiles can have a bool in the format file which tells getdata what 
| to do here)  We keep datasource->update() in order for syncronized 
| data sources to determine their one and only NF.  non-sycronized data 
| sources don't have to do anything here.

Exactly- the dirfile source is synchronous, but other sources don't have to be.  This is how the code works *right now*.  

| -INDEX always returns what you ask for, without wondering if the data 
| exists for any other fields.


| Seem sensible?

I think so :-)  Also, it *would* be possible for a datasource to have mechanisms for synchronous updates with fields of varying length- but such things are left up to the datasource (as they should be).


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