I would like to measure the angle between 2 vectors, is there a node to do that ? thanks

You want to take the dot product. Make sure your vectorz are normalized.

gl dude.

http://www.sidefx.com/docs/houdini10.0/expressions/dot [sidefx.com]

http://www.sidefx.com/docs/houdini10.0/vex/functions/dot [sidefx.com]

edit: oh yea, the result is the cosine of the angle so your angle would be the arcosine of the dot product.

To get the angle between two vectors you'll need to perform some operations using the dot (scalar) product between the vectors.

http://en.wikipedia.org/wiki/Dot_product [en.wikipedia.org]

You could do this using hscript, HOM, or VOPs.