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## 1. Introduction

Almost every weather website on the Internet has some sort of NEXRAD data display. Unfortunately almost all of these sites are only fulfilling a single purpose, allowing the user to view an image. Geographical Information Systems (GIS) goes beyond this single purpose model to allow the user to view the image, but then also process it within a GIS system. Processing could involve working with the RASTER data, reprojecting the image, querying the image, or many other things.

This HOWTO covers a mechanism to produce geo-referenced NEXRAD imagery from GEMPAK. As a GIS web mapping example, we use Mapserver to create a simple, but powerfull web application. This HOWTO assumes that you are running a modern version of Linux. Other UNIXs with GNU software installed should work as well.

This HOWTO is geared for those in the UNIDATA community with an active Internet Data Distribution feed and already have GEMPAK installed. If you don't have either of these, you will probably just be interested in the Mapserver sections. The radmapserver-files.tar.gz contains an example RADAR image ready for use with Mapserver or any other raster supporting GIS.

## 1.1 411 on abbreviations

Some of the abbreviations used in this HOWTO.

IEM | Iowa Environmental Mesonet
UNIDATA | University meteorological research group
NEXRAD | Network of Next Generation (WSR-88D) RADAR used by the National Weather Service
NWS | National Weather Service
GEMPAK | General Meteorological Application Package. Useful for dealing with NWS produced formats

Abbreviations

## 1.2 Reading this HOWTO

Some of you reading this may have no interest in generating the composites, but wish to use the composites. Currently, I am not aware of a group generating this data source for free. I have started generating a national base composite reflectivity as a proof of concept.

## 1.3 The Quick and Dirty version

The files used in this howto are available here: https://mesonet.agron.iastate.edu/docs/radmapserver/radmapserver-files.tar.gz.

- Download and install Proj.4 from http://www.remotesensing.org/proj/ .
- Download and compile Mapserver with proj, TIFF and PNG support from http://mapserver.gis.umn.edu . Place the resulting 'mapserv' binary in your webserver's CGI-BIN directory.
- Extract the radmapserver-files.tar.gz archive into your web root.
- Point your browser at http://your.host.name/cgi-bin/mapserv?map=/var/www/htdocs/radmapserver/radmapserver.map&layers=states .

## 1.4 Links

- UNIDATA
- Mapserver
  - Mapserver Docs
  - Mapserver WIKI

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