I'm trying to rotate a model around some axes, but this rotates it around the world origin. I understand that I need to translate the object relative to its own size before rotating it, but I don't know by how much.
I've done it by trial and error until now. How can I automatically read a model's width, height and position?
There are a couple ways.
This way shows how you can do it at runtime by grabbing out all the vertices to build the BoundingBox around the model.
The first answer on this page is super old but the basic idea applies to use a custom processor for your model in the content pipeline so you can compute the BoundingBox and store it in the Tag property of the model.
Generally it's better to do it in the content pipeline and store the data with the model that way your users don't have to wait for those redundant calculations each time they boot the game, but either approach should work.
