20030707: on the fly reconfiguration of LDM ldmd.conf NNEXRAD request

>From: David Fitzgerald <address@hidden>
>Organization: Millersville University of Pennsylvania
>Keywords: 200307071518.h67FI6Ld009772 LDM

Dave,

re: no existence of 2km N0R national composite in FNEXRAD
>Thanks, thats what I thought.

>One more question for you.  I would like to develop a web interface that
>would allow our faculty members to add or delete radar sites of their
>choosing to our ldm feed.  Of course, the program will have to make changes
>to the ldmd.conf file (at least).

If your network pipe is big enough, and you have enough disk space, and
your machine is fast enough to file the products as they come in, you
could simply request everything.  This would keep you from having to
stop and restart the LDM after each change to the ldmd.conf request.
There is another way, however.  See below.

>I am thinking along the lines of how the FNEXRAD
>floater sites are picked by Eric Horst via the Unidata web site and the map
>of radar sites. >Does something like this already exist?

Not that I know of.  At least, we have not developed such a
facility/procedure.

>If so
>may I take the code and modify it for our own use?  If no one has done this
>before, I would be glad to share the code with the community.   Eventually I
>would like our faculty to be able to add any feed they wish, not just radar,
>and have the program automatically make changes to the ldmd.conf/pqact.conf
>files.

Interesting project...

>To get started, may I use the code for the FNEXRAD floater?

I am not sure that this is what you really want or need.  The creation
of the FNEXRAD floater stream depends on all of the NEXRAD Level III
stations and products already being available on the machine that
originates the FNEXRAD stream.  A web interface allows a site to select
the floater sites' IDs, and these are written to an ASCII file in
~ldm.  A different routine runs out of cron to see if the list of
floater sites has changed, if it has, a program (executable code) that
puts the Level III floater products into the FNEXRAD stream is stop and
restarted with a different set of site IDs.  The LDM is not stopped and
restarted since all of the NEXRAD products needed are flowing through
the machine already.

It seems to me that your job would be somewhat different.  You would
have to build:

- web selection of desired sites

- generation of a modified ldmd.conf file
- create a facility that would validate your ldmd.conf entries
- stop and restart the LDM

-- OR --

- run a separate rpc.ldmd routine that requests the specific stations
  from your upstream host.  You would setup this separate invocation to
  write to the same LDM queue (so that duplicate products would be
  detected and eliminated), but since it would not be in the same
  process group as the "mainstream" LDM routines (those started by
  virtue of an 'ldmadmin start'), it would be up to you to monitor
  this invocation to make sure that it continues to run AND gets
  shut down if you need to remake the queue, or make changes to the
  feed request.

If your intention is create a facility that would allow your users
to select all of the streams to be ingested, then you would in essence
be moving away from using ldmadmin to start the data requests.  This
seems doable albeit a little messy.

>Thanks!

I could send along the various scripts and program source code that
we run to create the FNEXRAD floater stream, but it might just confuse
the issue.  If you still want it/them, I will have to touch base with
other folks here to get the full list of code to send.  Please let
me know.

Tom