I am new to heightfield in houdini 16.5.

I am currently working on river/road generation using houdini.

After watching video from Horizon Zero Dawn, I managed to create something like that.

But there is still a problem: How to get the normal vector of such heightfield?

In Horizon Zero Dawn, they use a negated volume gradient vector add (0,1,0) for normal. This can work, but may not be the right answer.



I convert the height field to polygon, then use a intersect node and primnormal node to get such normal. But this cost too much performance.

Is there a good way to get this normal please?

Back then in that video I was actually playing around with heightfields for the first time

Although the Volume Gradient gives you a nice "normal" when sampling a 3D volume it doesn't with a 2D heightfield.
It seems to not have a vertical Y component.
Actually the values in X and Z are the rate of change in height (Y) over those dimensions.
This is different than the X and Z components of the normal you are looking for.
But we can use the X and Z values to calculate a proper normal.

What you can do is the following in VOPs.

• Use a Volume Gradient VOP to sample the gradient of the heightfield.
  
• Use a Vector To Float VOP to split the components.
  
• Connect the X and Z components to the two Y inputs of Float To Vector VOPs.
  
• On the Float To Vector 1 that has the X as input to Y, set the X to 1.
  
• On the Float To Vector 2 that has the Z as input to Y, set the Z to 1.
  
• You have now created two tangent vectors.
  
• Now connect the two tangent vectors to a Cross VOP...
  
• ...but in reverse order: Float To Vector 2 to 1st input and Float To Vector 1 to 2nd input
  
• The output of the Cross VOP is you normal
  

benS