Using the Decoders

Configuring the LDM to Run the Decoders

Even though they can run "by hand", LDM-MCIDAS decoders are typically run as actions of the LDM's pqact utility. Five decoders, pnga2area and pngg2gini, nldn2md, proftomd, and zlibg2gini, are used to decode PNG-compressed MCIDAS (Unidata-Wisconsin) and FNEXRAD imagery, NLDN lightning data from SUNY Albany, FSL2 Wind Profiler data, and Zlib-compressed NOAAPORT GINI imagery, respectively. Decoded imagery is usable in all Unidata supported application packages (i.e., GEMPAK, McIDAS, and IDV); non-imagery products are decoded into McIDAS-compatible formats.

Additional decoders included in the LDM-McIDAS distribution do not work on current datastream products, but continue to be included for sites that have archives of Unidata-Wisconsin products included in the IDD before July of 1999:

cdftomd, nids2area, gunrv2, lwfile, lwtmd2, and lwtoa3 decode FSL Wind Profiler, WSI NIDS, and pre-2000 Unidata-Wisconsin datastream products into McIDAS format data files. gunrv2, lwfile, and lwtmd2's use was obsoleted by the removal of GRID, TEXT, and MD files from the Unidata-Wisconsin datastream on July 1, 1999. lwtoa3's use was obsoleted by the switch to use of PNG-compressed images in the Unidata-Wisconsin datastream in August of 2000. cdftomd's use was obsoleted by the introduction of proftomd. nids2area can still be run to create McIDAS AREA files from uncompressed WSI-format NIDS products, but it is recommended that sites receiving WSI NIDS or IDD NEXRAD Level III products use the McIDAS-X 7.8+ NEXRAD LEVEL III ADDE server to access these data files instead.

After the LDM-McIDAS decoders are installed, you need to configure your LDM pqact.conf file to run the LDM-McIDAS decoders that you want to use. Annotated example pqact.conf entries for for the decoders can be found in LDM Pattern-Action File for LDM-MCIDAS Decoders. A stripped down version of this file suitable for inclusion in the LDM's pqact.conf file is available in ldm-mcidas-pqact.conf.all. To transfer this to your machine, hold down the Shift key while pressing mouse button 1 over the link.

The ldm-mcidas-pqact.conf.all entries were written assuming that you want to decode data into the following directories:


Output Data Directory





If you are using these same directory structures, configuring your LDM pqact.conf file should be as simple as copying the ldm-mcidas-pqact.conf.all entries you want to use into ~ldm/etc/pqact.conf, verifying the integrity of pqact.conf, and then sending a HUP signal to your LDM's pqact process (this assumes you are running reasonably current versions of the LDM; if you are not, please contact Unidata User Support for help).

   Type: cd ~ldm/etc
         <edit pqact.conf and add entries from ldm-mcidas-pqact.conf.all>
   Type: ldmadmin pqactcheck
         <correct any errors in pqact.conf>
   Type: ldmadmin pqactHUP

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Send questions/comments to <support-ldm-mcidas AT unidata.ucar.edu>.