A little while ago I wrote about using the i option to combine smaller
octrees into a larger one. This is described in chapter 8 of the Radiance
text, section 8.5 on large data sets. Page 467 give the following example:

oconv -f fl.lgt st.lgt cl.lgt -i e_twr.oct -i w_shr.oct ... > bridge.oct

My experience with this approach is that you will get an error message
complaining that the file "-i" cannot be found. If you reverse the arguments
to avoid this message by placing the i options first followed by -f and the
.lgt files (or rad files in my case), then only the last i option (say
w_shr.oct) is included in the output octree (bridge.oct in this case). The
only way of combining octrees that works for me is the approach of using the
octrees as instances as described on the same page 467 in the text. Could
someone clarify how the i option can be used?