Directx 9 Terrain collision

Question

I searched and I found some tutorials how to do terrain collision but they were using .raw files, I'm using .x. But, I think i can do same thing they did. They took x,y,z values of an object can checked it against every single triangle in the terrain. It makes sense but It look like it will be slow. It is just like picking checking against every single triangle is slow.
Is there faster way to do it and good?
UPDATE
My terrain is not flat, if it was i would use bounding boxes.

Answer 1

Last time I did this, I used the Bullet library, and it worked great. It has various collision shapes to choose from, optimised for different scenarios, including general triangle meshes and heightfields. You can use the library's collision routines without the physics.

Answer 2

One common way to significantly reduce the time it takes to detect collisions is to organize the space into an octree , which will allow you to very quickly determine whether or not a collision could occur in a particular node. Generally speaking, it's easier to accomplish these sorts of tasks with a game engine.