how to convert vdb with constant resolution from .obj model?

[boringfish]

Hello everyone. Now I am trying to convert obj to vdb like that:

int exteriorWidth = 1.0f;
int interiorWidth = 1.0f;
openvdb::math::Transform::Ptr transform = openvdb::math::Transform::createLinearTransform(1.0 / (512 - 1));
openvdb::FloatGrid::Ptr sdfgrid = openvdb::tools::meshToSignedDistanceField<openvdb::FloatGrid>(*transform, mesh.points, mesh.triangles, std::vector<openvdb::Vec4I>(), exteriorWidth, interiorWidth);

The obj is normalized. I want the max dim of the transformed vdb (ActiveVoxelBoundingBox) to have the constant 512 resolution. However, this max dim is always 511 or even 513. So, how can I get the constant 512 resolution sdf vdb? Thank you very much!