[IDD #FPV-741226]: Few quick questions about ldm and decoder.

Hi Chuan-Yuan,

re:
> I was asking to download the nexrad dataset via ldm server.
> Here is what I found from internet and used in my ldm pact.conf
> 
> NMC3  ^SDUS[45][24] .... (......) /p(...)(...)
> FILE  -strip data/ldm/nexrad/%y%m\1\2.nmc3

Comment:  We prefer to use the primary name for IDD feed type, not
the alternate names.  The primary name for the feed type in this
action is FNEXRAD, and the alternate names are FT13 and NMC3.

The list of IDD feed types shows the correspondence between primary
and secondary names:

Unidata HomePage
http://www.unidata.ucar.edu

  Software -> LDM
  http://www.unidata.ucar.edu/software/ldm

    Documentation
    http://www.unidata.ucar.edu/software/ldm/ldm-current/

      LDM feedtypes
      
http://www.unidata.ucar.edu/software/ldm/ldm-current/basics/feedtypes/index.html

re:
> NEXRAD   ^SDUS[23578][24] .... 
> ([0-3][0-9])([0-2][0-9])([0-6][0-9]).*/p(...)(...)
> FILE  -strip   data/ldm/nexrad/NIDS1/\5/\4/\4_(\1:yyyy)(\1:mm)\1_\2\3
> 
> NEXRAD3  ^SDUS[23578][24] .... 
> ([0-3][0-9])([0-2][0-9])([0-6][0-9]).*/p(...)(...)
> FILE  -close   data/ldm/nexrad/NIDS2/\5/\4/\4_(\1:yyyy)(\1:mm)\1_\2\3
> 
> NEXRAD   ^SDUS[2357][24] .... 
> ([0-3][0-9])([0-2][0-9])([0-6][0-9]).*/p(N0.)(...)
> FILE  -close   data/ldm/nexrad/NIDS3/%y%m\1\2.nexrad

Like my previous comment, the primary name for this feed is NEXRAD3.  While
NEXRAD is an acceptable alternate name, for readability it is better to use the
primary name.

re:
> But I don’t quite understand what it means, could you answer some of my
> questions for me?
> 
> 1. I think, in order to request those of data, I need to request NMC3 and 
> NEXRAD from ldmd.conf
> So, I do this in ldmd.conf
> 
> REQUEST NMC3 ".*" coriolis.met.tamu.edu:388
> REQUEST NEXRAD ".*" coriolis.met.tamu.edu:388
> REQUEST FNEXRAD ".*" coriolis.met.tamu.edu:388

Comments:

- it is better to use the primary names for feed types

  When you switch to consistent use of primary feed type
  names, you will see that the first and third REQUEST lines
  are the same, and so redundant.

- 388 is the default port, so inclusion of :388 is
  not needed

I recommend that you change your REQUEST lines to:

REQUEST NEXRAD3 ".*" coriolis.met.tamu.edu
REQUEST FNEXRAD ".*" coriolis.met.tamu.edu

> But I don’t think NMC3 is working, and it looks like NEXRAD and FNEXRAD
> are the same thing?

I don't know why NMC3 would not work, it should as long as the upstream
machine, coriolis.met.tamu.edu, is receiving the FNEXRAD data, AND it
has an a ALLOW that allows you to REQUEST that data.

When you review the LDM feed types page, you will see that NMC3 is the
same as FNEXRAD, and NEXRAD is the same as NEXRAD3.

re:
> 2. I want to download the data within the domain of southern of USA,
> which is along the Gulf of Mexico. Do I refer it right ? [24]
> I think 2 is the florida, and 4 is the south central of USA

I don't think that the NEXRAD Level III stations are grouped as nicely
as you want/need.  Since you are only interested in a subset of the
available NEXRAD Level III stations, it is probably better to generate
a list of stations that you want to receive data from and then
modify your ldmd.conf REQUEST line to include the list of stations you
want.  Here is a simple example that will REQUEST just the NEXRAD Level
III data from Florida:

REQUEST NEXRAD3 "K(BYX|EVX|JAX|MLB|TBW|TLH)" coriolis.met.tamu.edu

re:
> 3. What is the SDUS[23578] means?

The '[23578]' is a regular expression.  SDUS[23578] is equivalent to
SDUS2 or SDUS3 or SDUS5 or SDUS7 or SDUS8.

re:
> all of the example said “SDUS” and the indicator is 2, 3, 5, 7, and 8.
> I have download the “xr05_X_ref_by_TT.xls”, but still quite not sure
> what those of number means.

I am not familiar with “xr05_X_ref_by_TT.xls”, so I can't comment on
what it means.

re:
> 4. What is “-close” and “-strip” means?
>    for nexrad data, should I use -close or -strip ?

If you performed a new LDM installation, then you should have the
file ~ldm/etc/pqact.conf that contains an explanation of what these
and other flags mean.  If you replaced your pqact.conf file with one
that someone has edited, this information may not be available anymore.
It can always be found in the LDM documentation on our web site.

We recommend that you include the '-close' option in your NEXRAD3
FILE action.  The '-strip' option is not needed.

re:
> 5.    What is \5/\4/\4_(\1:yyyy)(\1:mm)\1_\2\3 standing for?

The '\n' (\1, \2, ...) refers to fields that are enclosed in parentheses
in the pattern-action file entry being used.  For instance:

for:

NEXRAD ^SDUS[23578][24] .... ([0-3][0-9])([0-2][0-9])([0-6][0-9]).*/p(...)(...)
     FILE -strip data/ldm/nexrad/NIDS1/\5/\4/\4_(\1:yyyy)(\1:mm)\1_\2\3

\1 refers to the field that matches ([0-3][0-9])
\2 refers to the field that matches ([0-2][0-9])
\3 refers to the field that matches ([0-6][0-9])
\4 refers to the field that matches the first (...) in /p(...)(...)
\5 refers to the field that matches the second (...) in /p(...)(...)

For a product that has the LDM/IDD Product ID 'KAMA 221622 /pN3UAMA !nids/'
these fields become:

\1 -> 22
\2 -> 16
\3 -> 22
\4 -> N3U
\5 -> AMA

The (\1:yyyy) says to use the day represented in \1 to determine the
year of the data, which is currently 2016. \1:mm will expand to 12
as the current month is December, or month number 12.

re:
> To now, it is all about the LDM.

The best thing for you to do is to work through the LDM workshop materials
on our web site.  The answers to the questions you have posed should become
clear after you have gone through the training materials.

re:
> I do download some da/usr/bin/ld: cannot find -lldmtaset,

I do not understand what you are trying to tell us with this statement.

re:
> and trying to use py-art as the decoder.
> However, I didn’t find out any available documents saying from ldm
> download data to netcdf format, or even plotting.

I do not know of a Python "decoder" that can correctly handle all of
the NEXRAD Level III products delivered in the NEXRAD3 feed of the
IDD.  As far as converting the products to netCDF, most sites work
with the Level III data in its native format.

re:
> Thanks

No worries.

Cheers,

Tom
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Ticket Details
===================
Ticket ID: FPV-741226
Department: Support IDD
Priority: Normal
Status: Closed
===================
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