In Quake, this is really left up to the mapper. The Quake BSP compiler starts bisecting volumes from the origin (0, 0, 0). So, in order to produce a more balanced and BSP-friendly map, the mapper should center their geometry, on all three axis, around the origin.
I think a similar strategy could apply to your problem. Find the absolute bounds (mins and maxs) of your BSP nodes, and calculate the point in the center. That is where you should begin partitioning your tree. Now, unless your map is perfectly symmetrical, you will never achieve a perfectly balanced tree. But, for practical purposes, this gets you relatively close.
In Quake, this is really left up to the mapper. The Quake BSP compiler starts bisecting volumes from the origin
(0, 0, 0). So, in order to produce a more balanced and BSP-friendly map, the mapper should center their geometry, on all three axis, around the origin.I think a similar strategy could apply to your problem. Find the absolute bounds (mins and maxs) of your BSP nodes, and calculate the point in the center. That is where you should begin partitioning your tree. Now, unless your map is perfectly symmetrical, you will never achieve a perfectly balanced tree. But, for practical purposes, this gets you relatively close.