# question about projectpixelto3dray

Hi

I have a question about the function projectPixelTo3dRay, according to the API the return value is a 3d ray passing through (u,v).

But what does that mean? Why Z is 1? How I can calculate the point where it intersects the ray with the floor (Z = 0)?

Thanks

Thanks domhege, but how I can transform between the camera system and the system floor? you know any example?

Use the tf library. Obviously someone, somewhere must compute this transformation, i.e. where is the camera relative to the floor.