Volume sample rgb 'vel'

[saka]

hi,

please tell me, how to paint volume shadding with volume fields.

I have used volume_sample_rgb that the channel is "vel",

but it shows "black" only.

houdini geometry with VDB_Cache , or Arnold_prosedural loading VDB_Cache,

both is same black.

i can shade with "vel" in viewport,it seems to be well.

thanks.