Hello,

There is a shading derivative vop in SHOP context but I wonder how to get the curvature of a mesh in SOP.

Thanks for your help

Vincent

Measure SOP?

not bad really ! Thanks for the info.

Now is there any chance to explain how to isolate concave and convex curvature in SOP ?

++

Vincent

You can do that inside of vop. For instance by getting a dot product of a point normal and all the vectors pointing towards its neighbours (one by one) then adding these together and calculating their average. If the result is positive, it'c convex, if negative, it's concave. It's not particularly precise, but it did the trick for me.

You can have a look at the vop in the attached hip file. the values are normalised and mapped to colour to see what's going on. If you want to flip the values, just invert the threshold.

very nice

thanks a lot.

++

Vincent

Hi all,

Just trying to get this working with the new for loops in vops and I can't seem to get it happening.
Any ideas what I might be doing wrong here? Just trying to get the basics of it working…



Scene file [peterleary.com]

Thanks,
Pete

I know this is way late, but I was working on the same problem today and this thread came up in a search.

On the for loop, you need to add a float output for the cumulative angle, ie _angle. That will add “_angle_in” and “_angle_out” to the for nodes. After the dot product, you need to add the result to _angle_out on the for_begin before feeding it into the end_for. That will cumulatively add the angles between the original point and each neighbour.

After the for loop, you need to divide your results by the neighbourcount to get the average angle. Finally, use a fit to map the results (which will be -1 for maximum concavity to 1 for maximum convexity) to 0 to 1 for Cd.

Hmmm….kinda looks like a Houdini 16 image was just posted outside of the Houdini 16 forum the week before release, but you wouldn't do that, would you?

Damn! I missed it!!
Hey thanks Pyraxis, you wouldn't have a scene example would you?

Chris, I'm so sorry. I had the release dates mixed up.

Hi peteski, here's a sample scene, hope it helps!

Does somebody know how to use the shading derivative to create a curvature shader?
This is my wrangle version of the curvature pointvop posted here.

Hey thanks for sharing that!

Pyraxis
Hi peteski, here's a sample scene, hope it helps!

Hey man, can you, or someone else, explain me what is going on in the ‘output: _angle’ and its add with the dot.product in the loop node? I can understand all the rest of the process but not these in particular.