The file format Open-SPX is a 3d image format developed by interzart around 2000, and released open source with the GPL. I've got some images in that format, which I want to import into a more modern editing program, but I can't find anything that can open/covert them. I've tried searching online, but it looks like interzart is gone, and I couldn't find any evidence of SPX files.
I'm looking for either a way to convert them to a modern format, or source code or documentation showing how I can write something that can read them.