how to calculate gradient tangent ?


#1

I’ve got a gradient vector field generated with -gradient -a[0,1,2]
but I’m looking for the tangent of that.
I mean if my vector is V(x,y) coordinates I’m looking for T=V crossproduct [0,0,1] that should be tangential to V.
I hope this make sense.
how could I do that ?
luc


(David Tschumperlé) #2

I’m not sure what you want to do precisely, but you can easily compute the cross product between a vector-valued image (with 3 channels) and [0,0,1], like this:

$ gmic input image3channels.jpg fill "cross(I,[0,0,1])"

#3

yes.this is exactly what I needed.thanks a lot , fill was the missing element.I got it now!


(David Tschumperlé) #4

Note also that for this particular case :

[ X Y Z ] x [ 0 0 1 ] = [ -Y X 0 ]

So computing this particular cross product is faster with:

fill "[ -G R 0 ]"

#5

bien vu.thanks David