Minutes from 69th OpenVDB TSC meeting, Nov 3rd, 2020, (EDT)

Attendees: *Nick* A., *Jeff* L., *Ken* M., *Dan* B.

Additional Attendees: Johannes Meng (Intel), JT Nelson (Blender),
Andre Pradhana (DW), Bruce Cherniak (Intel)

Regrets: *Peter* C.

Agenda:

1) Confirm quorum
2) Secretary
3) Timezones
4) OpenVDB Grid Layout (Cell centered vs Node centered)
5) Next Meeting

1) Quorum was confirmed.

2) Secretary was Nick Avramoussis

3) Timezones

Agreed to move with daylight savings - i.e. whatever the meeting invite says!

4) Node Value Locations (Cell centered vs Node centered)

A user has run into issues where the distinction between how values may
potentially be stored in OpenVDB numerical grids vs OpenVDB Points grids was not
clear. The problem is essentially that methods to retrieve node bounding
information from a given VDB do not necessary respect the positioning of cell
values. This is especially true for CoordBBoxs whose integer coordinates can
either represent the minimum to maximum-1 bounds (Node centered) OR the
minimum-0.5 to maximum+0.5 bounds (Cell centered). The distinction between the
two is left to the underlying algorithm. Comments were made in regards to the
position information of points within a PointDataGrid. Points are stored
relative to the cell center; that is their voxel offsets are between -0.5,+0.5
and not 0,1. This difference is irrelevant when considering the fast discarding
of candidate nodes; instead one must account for the differences of a volume
modeling a continuum and a points grid with discrete data stored potentially
throughout a given cell. Jeff observed that the ray intersection code could
potentially be incorrect for cell centered values. All agreed that better
documentation is a must. Nick, derived or specialized implementation of bounding
boxes which represent either state with clearer API methods would also help show
this distinction. Ken to investigate further and draw up images representing the
problem for further discussion and to hopefully include in the docs.

5) Next Meeting

Next meeting is November 10th, 2020. 1pm-2pm EDT (GMT-4).
