This is not for the faint of heart, and should not be needed in 1.5.0 onwards releases since we have a fallback system based on a property file. These instructions are here mainly for the curious that wants to know a little more about the EPSG database subsystem.

Since the implementation of the HSQL database in the WCS branch of Geoserver for storing EPSG projection codes,
specifying a custom projection is a bit more tricky than simply making an entry in the epsg.properties file.

To define my projection, I edited the EPSG.sql file. This file is used to create the cached EPSG database.

1. Change into your geoserver/WEB-INF/lib directory
2. Uncompress the gt2-epsg-h.jar file:

   jar xvf gt2-epsg-h.jar

    
    
    
    

3. Open the org/geotools/referencing/factory/epsg/EPSG.sql file with a text editor. To add a custom projection, these entries are essential:
   • an entry in the EPSG_COORDINATEREFERENCESYSTEM table:

     (41111,'WGC 84 / WRF Lambert',1324,'projected',4400,NULL,4326,20000,NULL,NULL,'US Nat. scale mapping.','Entered by Alex Petkov','Missoula Firelab WRF','WRF','2000-10-19','',1,0),

      
      
      
      
     where:
     1324 is the EPSG_AREA code that describes the area covered by my projection
     4400 is the EPSG_COORDINATESYSTEM code for my projection
     20000 is the EPSG_COORDOPERATIONPARAMVALUE key for the array that contains my projection parameters

   • an entry in the EPSG_COORDOPERATIONPARAMVALUE table:

     (20000,9802,8821,40,'',9102), //latitude of origin
     (20000,9802,8822,-97.0,'',9102), //central meridian
     (20000,9802,8823,33,'',9110), //st parallel 1
     (20000,9802,8824,45,'',9110), //st parallel 2
     (20000,9802,8826,0.0,'',9001), //false easting
     (20000,9802,8827,0.0,'',9001)  //false northing

      
      
      
      
     here 9802 is the EPSG_COORDOPERATIONMETHOD key for the Lambert Conic Conformal (2SP) formula

   • an entry in the EPSG_COORDOPERATION table:

     (20000,'WRF Lambert','conversion',NULL,NULL,'',NULL,1324,'Used for weather forecasting.',0.0,9802,NULL,NULL,'Used with the WRF-Chem model for weather forecasting','Firelab in Missoula, MT','EPSG','2005-11-23','2005.01',1,0)

      
      
      
      
     where
     1324 is the EPSG_AREA code that describes the area covered by my projection
     9802 is the EPSG_COORDOPERATIONMETHOD key for the Lambert Conic Conformal (2SP) formula

4. Observe the commas. If you enter a line that is at the end of an INSERT statement, the comma is omitted (make sure the row before that has a comma at the end).
   Otherwise, add a comma at the end of your entry. After all edits, save the file and exit.
5. Compress the gt2-epsg-h.jar file:

   jar -Mcvf gt2-epsg-h.jar META-INF org

    
    
    
    

6. Remove the cached copy of the EPSG database, so that can be recreated. On my Linux machine, it resides in my /tmp directory:

   rm -rf /tmp/Geotools/Databases/HSQL

    
    
    
    

7. Restart Geoserver

Hopefully now the new projection will be successfully parsed. To verify that indeed my work succeeded, I listed the recognized projections by going to http://localhost:8080/geoserver/srsHelp.do

Here is the reported entry for my projection in the browser:

!projection.png!