Unidata - To provide the data services, tools, and cyberinfrastructure leadership that advance Earth system science, enhance educational opportunities, and broaden participation. Unidata
    •      
  advanced  
 
Previous: Introduction Next: Introduction: GEMPAK Capabilities Table of contents Frames User Manual GEMPAK Online Tutorial > Introduction

3.0 Introduction: What is GEMPAK?

What is GEMPAK?

GEMPAK, the GEneral Meteorology PAcKage, is a suite of applications programs for the analysis, display and diagnosis of geo-referenced data. GEMPAK was orginially developed by the Severe Storms Laboratory at the Goddard Space Flight Center of NASA starting in the early 1980's. The Unidata program center release of GEMPAK/N-AWIPS incorporates several additions developed both locally and at COMET to enhance the use of realtime data aquired through the IDD, as well as instructional case studies.

How does GEMPAK work?

As a software package, GEMPAK is made up of application programs, libraries, graphics routines, and device drivers. Each time GEMPAK is used to analyze and display data some or all of these components are used. For example, the user (you) runs an application program like SFMAP, the surface mapping program. In order to do the scientific data analysis that GEMPAK is so well known for, the application program calls on a suite of library routines which do everything from parsing your input to calculating complicated grid diagnostics.

When the graphic is ready to be constructed, the application program (SFMAP) starts up a separate graphics program. This GPLT graphics process handles all the graphics processing including mapping, symbol drawing, and coordinate transformations. When the graphic is ready to be output, a third process called the device driver starts up. The device driver could be any one of several GEMPAK drivers available. For example, it could be a process to draw the picture to an XWindow (XW), or it could be a process to write out instructions to a Postscript file (PS).

Each of the three processes (the application program SFMAP, the graphics process GPLT, and the device driver XW) are separate, and communicate with each other using message queues. Message queues behave like mail boxes. One process leaves a message in the mail box for the other process. Upon receipt of a message, the other process acts on the information in the message, and perhaps sends a message back to the first process, or to another process via another mail box.

When you are finished using one application program, SFMAP, you can exit the program and the SFMAP process and it's mail box go away. Then you can run another GEMPAK program, perhaps GDCNTR the gridded data contouring program, and it will hook up with the already running GPLT and XW processes. In this way, many different GEMPAK programs can use the same graphics and device driver processes. This functionality allow you to construct overlays, and well as multi-paged Postscript files. The GPLT graphics process and the device driver will continue to run in the background of your computer until you tell them to go away. You can do this by running another GEMPAK program called GPEND (for GraPhics END).

 


Previous: Introduction Next: Introduction: GEMPAK Capabilities Table of contents Frames User Manual GEMPAK Online Tutorial > Introduction

 
 
  Contact Us   •   Site Map   •   Search   •   Terms and Conditions   •   Privacy Policy   •   Participation Policy
 
National Science Foundation (NSF) UCAR Office of Programs University Corporation for Atmospheric Research (UCAR)   Unidata is a member of the UCAR Office of Programs, is managed by the University Corporation for Atmospheric Research, and is sponsored by the National Science Foundation.
P.O. Box 3000   •   Boulder, CO 80307-3000 USA   •   Tel: 303-497-8643   •   Fax: 303-497-8690