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Measure Geometry Thickness

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moonlightkiss02
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Hi
Long time since I posted.

I have an animated horse that I'm trying to measure the thickness of different parts - legs, body, head, ears, etc. I basically want to pump it into color but I'm having a hard time generating a procedural way to measure an attribute for thickness.

The idea is that the thinnest parts change color first.

Any help!?

Thanks!
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moonlightkiss02
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I'm told this is very easy to do in lightwave so I'm wondering how to do it in Houdini.
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circusmonkey
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Not sure what your end goal is and how you are going to use the data. You could use the a vop sop to calculate the bounding box value of some points and colour them based off the bounding box value.

see attached

Attachments:
colourdepth.hip (84.5 KB)

Gone fishing
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eetu
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You could raycast along the viewdirection and see how far the next hit is. Very minimal shader attached.

Attachments:
ee_thickness.png (60.4 KB)
ee_thickness.hip (83.6 KB)

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buki
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it would be nice and a reliable way to do this in sops, it would be very useful
daniel bukovec | senior fx td | weta digital
qLib -- http://qlab.github.io/qLib/ [qlab.github.io]
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mawi
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…deleted post.
Edited by - Dec. 11, 2014 13:13:32
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old_school
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Did a 30 second Google search wrt Lightwave, didn't find much… What I did find was scant reference to thickness being evaluated from a “surface thickness gradient”. No other info so I am assuming that you need to bake a map out by rendering which fires rays??? Assumption here…

Whatever…

The firing rays works very well to evaluate thickness and you don't have to resort to the VOP SOP approach as you do have to correct those “perfect” cases such as fingers where the tips can fire right up to the shoulder anyway, and VOPs this means recursing over neighbours which means point clouds, blah. Just use a couple Attribute Promotes and a smooth.

Done.

See the attached file.

Attachments:
thickness_surafce_evaluation.hip (87.5 KB)

There's at least one school like the old school!
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mawi
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mawi
Take out a vector to camera.
Raycast each point with a intesect3D vop against the geometry.
It will return -1 if it didnt hit anything.

Keep in mind that the length of the direction vector is the max search distance.



But this isnt the “cull hidden points” thread.
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moonlightkiss02
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I definitely want to do it in SOPs and not in a shader. OK, I'm going to start looking at each of your suggestions, thank you!! Be back with you soon!
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moonlightkiss02
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Jeff nailed it! That's exactly what I'm looking for. I'm not very strong with the wrangle sop. I notice in the last wrangle you create a weight float but it never shows up in the spreadsheet. Is that because it then becomes the color?

Thank you!
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old_school
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Excellent vex wrangler question. With the wrangler, I declare a local variable with the type something like this:
float my_variable = 1.0;
When you do that, my_variable will not be exported to the geometry and is only local for the current iteration through the points. It is local to the SOP.

As opposed to this:
@my_bound_variable = 1.0;
will add the float “my_bound_variable” to the geometry as a float type attribute to be used in subsequent SOPs.

It's wise to only add the additional attributes you need later on. You can quickly add geometry bloat.
There's at least one school like the old school!
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moonlightkiss02
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OK, that's cool!

So I ended up putting it into a VOPSOP for a little more artistic control but kept your version to switch between. I'll probably make it an asset for the company I'm at. Seems super handy!

A couple things I noticed:

1)the peak was renamed after the first wrangle and the network still worked for me, which is odd.

2)The horse geometry I've included for some reason didn't play well with the subdivide and point sops. The point sop errors saying it can't evaluate NX, NY, NZ. If I add the normals before the subdivide it works, but I'm not sure why the normals would error out from the subdivide.

Attachments:
thickness_surafce_evaluation_108.hip (1018.2 KB)

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PradeepBarua
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1)the peak was renamed after the first wrangle and the network still worked for me, which is odd.

Because peak value of 0.001 is very minimal and dist is equal to dist minus this value (@dist -= ch(“/obj/sphere_object1/peak_avoid_self_collision/dist”). As there is wrong reference so dist = dist. So you do not notice much difference.
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PradeepBarua
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2)The horse geometry I've included for some reason didn't play well with the subdivide and point sops. The point sop errors saying it can't evaluate NX, NY, NZ. If I add the normals before the subdivide it works, but I'm not sure why the normals would error out from the subdivide.

Your geometry already have vertex normal. That's why point sop errors out.
Just delete vertex normal or promote it to point. If you promote it then you don't need point sop.
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PradeepBarua
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PradeepBarua
Because peak value of 0.001 is very minimal and dist is equal to dist minus this value (@dist -= ch(“/obj/sphere_object1/peak_avoid_self_collision/dist”). As there is wrong reference so dist = dist. So you do not notice much difference.

wow!!! wrangle's semicolon and my close parentheses giving me this sign. never mind
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pelos
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interesting, I am assuming with this you can only get thickness base on the camera angle/per frame?
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grayOlorin
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if you are looking for thickness based on 3D locality and not camera based, I recommend looking up medial axis of 3D meshes. I used something like it to calculate thickness of tree branches to drive stiffness. I put an RFE for this with SESI as a very useful atomic SOP to have for different things, but we did a poor man's implementation at my studio for our purposes.

This is probably one of my favorite papers on it. You do not have to nail it exactly, but even an approximation using the ray SOP may get you there:

http://web.siat.ac.cn/~huihuang/Skeleton/Skeleton_page.html [web.siat.ac.cn]
-G
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littlegreenlantern
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Ooh, that skeleton algorithm sounds like it would be super useful. Is there a way to do this in Houdini currently?
Ben Andersen
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Chassaigne Victor
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Hello

New to VEX , I open jeff file but i don't understant this line “ @dist -= ch(”/obj/sphere_object1/peak1/dist“);”

What doest -= means ?

Thanks

victor.
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BabaJ
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The attribute @dist has a certain value before the line of code you show is executed,

after that line is finished the value of @dist will have had the value from the channel reference ch(“/obj/sphere_object1/peak1/dist”) subtracted from it.

it could have easily been += which would have had the channel reference added,

and if *= multiplied by it.

In the line you reference it is a short form for the same thing as this:
@dist = @dist - ch("/obj/sphere_object1/peak1/dist");
Edited by BabaJ - June 18, 2018 19:02:40
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