Tutorial: Converting VDB files to NanoVDB via OpenVDB in C++

Mon, 27 Jun 2022 00:00:00 +0000

VDB files are commonly used for storing volumetric density grids, such as clouds or smoke. Blender, Embergen, Houdini are a few sources of such data. More recently there is a sparse specification, called NanoVDB, storing sparse voxel octrees (SVOs) that is a more optimized representation for GPU rendering.

I’m outlining steps for Ubuntu, but these libraries are supported on Windows as well with a bit more setup.

build / install OpenVDB check here for cmake instructions
open your terminal and install libtbb
```
sudo apt install libtbb-dev
```
OpenExr is a dependency of OpenVDB, so this should already be built w/your version of OpenVDB

Here are the interesting excerpts from the OpenVDB library that you need to convert between VDB and NanoVDB:

...
#include "nanovdb/util/OpenToNanoVDB.h"
#include "nanovdb/util/IO.h"
...
 openvdb::initialize();
 openvdb::io::File file(argv[1]);
 file.open();

 openvdb::GridBase::Ptr baseGrid;
 for (openvdb::io::File::NameIterator nameIter = file.beginName();
 nameIter != file.endName(); ++nameIter) {
 // TODO: deal with other channels if you have them
 if (nameIter.gridName() == "density") {
 baseGrid = file.readGrid(nameIter.gridName());
 }
 }
 file.close();

 openvdb::FloatGrid::Ptr srcGrid = openvdb::gridPtrCast<openvdb::FloatGrid>(baseGrid);
 auto handle = nanovdb::openToNanoVDB(*srcGrid);

 // Write the NanoVDB grid to file
 nanovdb::io::writeGrid(argv[2], handle);
...

Find the complete source for my basic CLI example converting an input vdb file to a nanovdb file at https://github.com/bmahlbrand/openvdb2nanovdb-util

Openvdb | Ben Ahlbrand CV

Tutorial: Converting VDB files to NanoVDB via OpenVDB in C++