SDF + Volume Sample Question

[catchyid]

Hi, 

According to Houdini Docs, IsoSurface (SDF, Ray Intersect) should produce a volume such that if a vortex inside the input mesh it has a negative value, zero at the surface, and positive outside. To test it, I used "Sample Volume" VOP, but I always get the same value?? When I render the volume it's rendered right, so I am not sure what I am doing wrong

In the attached image,  "depth" attribute has a constant value? In the volume sample node, I read the second input so it's sampling the IsoSurface SDF volume...

Thanks,

 

[iamyog]

couple of things:

- did you specify which input to read in your volumeSampleFile1 ? Either change the input dropdown menu to Second Input, or connect Opinput2 to the filename, or promote the parameter and fill the path appropriately

- make sure the output type is set to SDF Volume on the isoOffsetSOP

- do not use addAttribute. From the doc: https://www.sidefx.com/docs/houdini/nodes/vop/addattrib

Quote

This does not change the attribute values. To change the value of the currently processed element, see the Bind Export VOP. To change other elements or other attribute classes, see Set Attribute VOP.

Just replace it by a bindExport.

- Finally... last but not least, you are trying to find the depth of each point of the sphere. They are by definition on the surface of the sphere.
That means you should have the same value for all points: 0 = on surface.
You will however see the depth attribute with values >0. This is because your are sampling a volume that is a representation of your sphere. The higher the resolution of your volume, the closer the depth attribute will be to 0, and the opposite.

[catchyid]

Wow, Thanks The culprit was  addAttribute node, when I used bind things got right. I really appreciate your detailed help