  A challenge in isogeometric analysis is constructing analysis-suitable
volumetric meshes which can accurately represent the geometry of a given
physical domain. In this paper, we propose a method to derive a spline-based
representation of a domain of interest from voxel-based data. We show an
efficient way to obtain a boundary representation of the domain by a level-set
function. Then, we use the geometric information from the boundary (the normal
vectors and curvature) to construct a matching C1 representation with
hierarchical cubic splines. The approximation is done by a single template and
linear transformations (scaling, translations and rotations) without the need
for solving an optimization problem. We illustrate our method with several
examples in two and three dimensions, and show good performance on some
standard benchmark test problems.
