Is there a way to show or calculate a histogram of a volume ?
I found a histogram function in the openvdb header files, but it doesnt seem to be accessible through houdini nodes …

You can probably do it in a Volume VOP by summing up the results into a new (detail) array attribute. I haven't looked at the OpenVDB histogram method but one needs to define the buckets that you want to sum over since it so clear for floating point values as it is for integer values.

This is much faster than it has a right to be.

I merge a 256 point line with my volume. Then in a volume vop, run setpointattrib() to accumulate each point of the line according to the density*256.


int pt = @density * 255;
pt = clamp(pt, 0, 255);

vector displace = {0, 1, 0};
displace /= 1000*1000;
setpointattrib(0, ‘P’, pt, displace, “add”);

Wow !
A histogram in the viewport ! I am astonished.

I am playing around with a python sop which uses numpy histogram to generate the buckets, but I could not get the resulting data into the GUI
I was trying to write the values into a ramp parameter of the pysop to show the histogram.

Just to bump this topic one more time. Is there a way to access the openvdb histogram function in houdini without c++ / hdk ?