Keeping camera above the terrain

Hi,

I now have my terrain and Camera and I can now rome over my small terrain..

Unfortunately .. some time my camera penetrates the terrain...

I know that i could do collision detection and know whether my camera is falling below the terrain or not...

Is there any better method... I thought to calculate the normal for all the traingles in the terrain and put them in an array later use this as a lookup table while moving my camera...

I want a good performance and a better FPS....

Please suggest me ... Any help would be appreciated...

Thanks,
Pradeep