Beginner Question, Calulate Y Length

[Dubtronics]

Hi,

I am trying to calculate the y distance of a cached fluid sim in a tank. and I would like to have a color going from from black at the bottom and white at the top. The idea is to then use this in Mantra to drive the roughness of the transparency or the tint to create an ocean shader. I am trying to do this using a vopsop, I have tried various methods that other people have tried and I can only get it partially right. most of the time it seems to be calculating the distance from the center rather than the Y distance. In the file attached I get the gradient at an angle rather than straight up. 

I am totally new to this and any help would be appreciated.
 

points_from_volume.hip

[3dome]

I'm at work so cant download the file but have you tried using the bounding box to drive the color? in a wrangle it would be something like

vector min, max = {0,0,0};
getbbox(0, min, max);
float remap = fit(@P.y, min.y, max.y, 0, 1);
@Cd = remap;

Edited March 29, 2018 by 3dome
forgot line of code

[konstantin magnus]

Alternatively:

@Cd = vector(relbbox(0, @P)).y;

 

[Dubtronics]

Thank you, I will try that. I tried something similar but i wasnt able to get the gradient  just a solid color.  I wanted to try to do it in VOP because i feel more comfortable with a node base approach rather than  VEX code.

[konstantin magnus]

5 hours ago, Dubtronics said:

try to do it in VOP

 

vertical_gradient.hipnc

[Dubtronics]

Thanks for different methods really helps me to understand the way things work.