iv to stl conversion is most likely related to export of 3D models from SGI Invertor 3D format (.iv) to a generic STL format for 3D printers. You can find several 3d modeling software that allow this particular conversion, especially those that support export for 3D printers. And of course you can also use some dedicated 3D model conversion solution.
Open IV file Open STL file3D viewer and converter with huge file type support
A website STL converter
A command line converter for 3D format
A 3D CAD translation software