Hi, After reading in an OpenVDB 4 file with point data, how does one

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How to create PointPartitioner from data that is read in ?,about academysoftwarefoundation/openvdb

Comments (3)

danrbailey commented on May 22, 2024

I'm currently working on getting the code samples and documentation ready for submission into OpenVDB, so that should help explain this better. In short, the PointPartitioner is only for use with a PointIndexGrid where the attribute data is stored in a linear external array.

Here's a super-simple example for iterating over position data in a PointDataGrid:

for (auto leafIter = grid.tree().cbeginLeaf(); leafIter; ++leafIter) {
    auto handle = openvdb::points::AttributeHandle<Vec3f>::create(leafIter->constAttributeArray("P"));
    for (auto iter = leafIter->beginIndexOn(); iter; ++iter) {
        const Vec3d voxelCoord = iter.getCoord().asVec3d();
        const Vec3d positionVoxelSpace = handle->get(*iter);
        const Vec3d positionWorldSpace = grid.transform().indexToWorld(positionVoxelSpace + voxelCoord);
        std::cerr << "Position: " << positionWorldSpace << std::endl;
    }
}

Hope that helps.

Dan

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nyue commented on May 22, 2024

Thank you.

In your code

leafIter->constAttributeArray("P")

How do you know there will be an attribute call "P" ?

How does one programmatically find all the other attribute names ?

Cheers

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danrbailey commented on May 22, 2024

"P" is a mandatory attribute.

For simple inspection, you can use some of the convenience methods on the PointDataLeaf:

bool test1 = leafIter->hasAttribute("P");
bool test2 = leafIter->hasAttribute(/*index=*/4);

Otherwise, you'll need to go through the Descriptor:

const AttributeSet::Descriptor& descriptor = leafIter->attributeSet().descriptor();
for (const auto& namePos : descriptor.map()) {
    const Name& name = namePos.first;
    const size_t index = namePos.second;
    const Name& valueType = descriptor.valueType(index);
}

Although the API doesn't enforce this, by convention we assume that the Descriptor is the same across all LeafNodes.

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