The GDAL Plugin provides access to all the raster and vector formats support by GDAL and OGR. You can find a complete list of raster and vector formats here:
All GDAL/OGR drivers are prefixed with "gdal_". For example, the GDAL driver code for the ERDAS Imagine file format is "HFA". The equivalent driver in OSSIM is "gdal_HFA". Here's an example of how to use the HFA driver in orthoigen:
ossim-orthoigen -w gdal_HFA input.tif output.img
Note that there is some overlap between formats supported via GDAL and the other plugins (e.g. jpeg, png, nitf, tif, etc.). Let's take PNG as an example. The PNG Plugin uses ossim_png. GDAL's png driver is called gdal_PNG. In orthoigen you can specify which writer to use using the -w argument. Example:
ossim-orthoigen -w ossim_png input.tif output.png
ossim-orthoigen -w gdal_PNG input.tif output.png
If the writer argument is not specified, OSSIM will use whichever plugin appears first in the ossim_prefs file. As a general rule of thumb, the GDAL plugin is approximately 2 times slower than the native ossim plugins.