I am looking for 3D composing and rendering software which has a text-based scene file format. I saw that there was such software that was free open source (e.g. GPL or BSD licensing) a couple years ago, but forgot what that was. I looked at Blender just now, but its format is binary.

The purpose for this is to, in step 1, compose a scene that acts as a template, and in step 2, generate additional elements for the scene, or modify the scene, with specific data used to control those elements. This data will change each time step 2 is done. The purpose is to do a 3D image of certain measured source data. And step 2 needs to be doable w/o the GUI interface so it can be run on servers. Step 2 will be done w/o any human activity (e.g. an hourly cron job, for example).

Any suggestions?

You could use the python interface in Blender -- btw in a lot of situations duplivert is your friend, you can put arbitrary 3d shapes at a lot of data points, fast -- and have blender run your script on load. That'll achieve supplying the new data as text or any format.

Most pure renderers accept textual scene descriptions. Were you thinking of povray?

I know of Povray. I just don't know how to classify it.

What I expect to do is use a 3D composition tool interactively to create the initial mockup of the scene I want, with the pieces that change being given some variations so I can see those changes in the scene file. Once I figure out what changes in that file, I can place that file hard coded into a script/program, and for the changing parts, insert code that gives the variation desired based on the input data. Output with be a similar scene file. That script/program will be run with various data to generate related images that depict that data. I want to do those runs on the server farm.