[daip] question about VLANT

[Eric Greisen]

Bryan Butler wrote:
> 
> eric,
> 
> i can't find a precise enough description of the algorithm to apply 
> baseline corrections.  it's not described either on the web page where 
> you can retrieve them, or in the VLANT help file.  i could parse the 
> code, but thought you might know the answer right away and save me some 
> time.
> 
> let me explain my confusion.
> 
> the baseline file contains lines like:
> 
> ;MOVED OBSDATE   Put_In_ MC(IAT)  ANT  PAD    Bx      By      Bz
> ;
>         JAN06     JAN06  20:30     8   N12  0.000   0.000   0.010
> JAN03   JAN10     JAN11  19:21    20   N18 -0.0017  0.0020 -0.0020
> 
> 
> now, for the second line, it's pretty obvious what observations to apply 
> the correction to (although, i have to say that there is still ambiguity 
> because of the unkown *time* of the move on jan03, but let's ignore that 
> for now).
> 
> but for the first line, there is no identification of a move date, so 
> how can you be clear on how far back from jan06 20:30 to make the 
> corrections?
> 
>     -bryan

The collection of VLA.ant.yyyy files is viewed as a continuous stream of 
information and the moved date will appear somewhere probably in the 
previous year - antenna positions are checked after moving but also at 
later dates if they do not move further.  If the putin time is after the 
observation and the antenna number and station match, the correction is 
added to the sum of the corrections.  If a moved date appears after the 
observation, then the antenna is removed from the list of those allowed 
to get corrections.  At the end, the task looks to see if the list still 
has antennas that could get corrections and says so if there are any.
There are usually 3 since some antennas only move when they go into the 
barn for maintenance or upgrade.

I found the description on the web pages a bit confusing but it is in 
fact adequate.  What was not adequate until I got involved were the 
correction files.  The ones now in the system have been themselves fixed 
by me and there is at least one range of dates in which it was not 
possible to determine what people had done - VLANT knows that range 
which was short and a long time ago.

Eric