Ivan Mincik has created a pgAdmin plugin that works as a command-line PostGIS viewer as well. The viewer could be useful for spatial databases administrators using pgAdmin.

It is not intended to add major functionalities to the viewer, but if it is required, it could be extended with all the power of Python and QGIS libraries. The PostGIS Viewer allows to display spatial tables and views from  spatial databases.

PREREQUISITES

Python, PyQt4, PyQGIS and libqt4-sql-psql.

How to install prerequisites in Windows: See this post.
How to install prerequisites in Ubuntu/Linux: For QGIS, see downloads official page. For the other programs use apt-get or Synaptic.

DOWNLOADS

For Ubuntu/Linux download the postgis_viewer.py file.

For Windows download postgis_viewer.py and postgis_viewer.bat

HOW TO USE THE VIEWER FROM A COMMAND LINE

Ubuntu/Linux: Set the execution permission:

 $ sudo chmod 755 postgis_viewer.py 

 $ postgis_viewer.py -h localhost -U postgres -W secreto -s public -t pais -d geodb & 

 $ postgis_viewer.py -h localhost -U postgres -W secreto -s public -t rios -d geodb  

Windows:

Be sure you have the QGIS libraries enabled and run in a command line:

 $ c:\Python25\python.exe postgis_viewer.py -h localhost -U postgres -W secreto -s public -t pais -d geodb &  

INSTALLATION AS A pgAdmin PLUGIN (PostgreSQL 8.4)

Ubuntu/Linux:
Copy the postgis_viewer.py file into one of the folders of the environment variable PATH, for instance, /usr/bin/

 $ sudo cp postgis_viewer.py /usr/bin/  

 $ sudo chmod 755 /usr/bin/postgis_viewer.py  

  Title=View PostGIS layer
  Command=postgis_viewer.py -h $$HOSTNAME -p $$PORT -U $$USERNAME -W $$PASSWORD -d $$DATABASE -s $$SCHEMA -t $$OBJECTNAME
  Description=View PostGIS layer
  Platform=unix
  ServerType=postgresql
  Database=Yes
  SetPassword=Yes 

Windows:

Copy the postgis_viewer.py and postgis_viewer.bat files to C:/Archivos de programa/PostgreSQL/8.4/bin/

Edit C:/Archivos de programa/PostgreSQL/8.4/pgAdmin III/plugins.ini adding the following lines:

  Title=View PostGIS layer
  Command="$$PGBINDIR\postgis_viewer.bat" -h "$$HOSTNAME" -p "$$PORT" -U "$$USERNAME" -W "$$PASSWORD" -d "$$DATABASE" -s "$$SCHEMA" -t "$$OBJECTNAME"
  Description=View PostGIS layer
  KeyFile=$$PGBINDIR\postgis_viewer.bat
  Platform=windows
  ServerType=postgresql
  Database=Yes
  SetPassword=Yes

The postgis_viewer.bat file sets the OSGeo4W environment variables (Qt, Python, QGIS) to allow the execution of postgis_viewer.py The .bat file assumes OSGeo4W is installed in C:/ and PostgreSQL can be found in C:/Archivos de programa/PostgreSQL/8.4/ You should check that file if you get some troubles while running the plugin.

NOTE:  The steps are based on PostgreSQL 8.4 and pgAdmin 1.10.

REFERENCES

• Ivan Mincik's PostGIS Viewer: https://github.com/imincik/QgsPostGIS-Viewer
  
• Send and receive a signal between 2 Qt applications: http://www.qtcentre.org/threads/38453-Send-and-receive-a-signal-between-2-Qt-applications.?p=176716#post176716
• Single Application: http://www.qtcentre.org/wiki/index.php?title=SingleApplication