  For numerical simulations of cosmic-ray propagation fast access to static
magnetic field data is required. We present a data structure for
multiresolution vector grids which is optimized for fast access, low overhead
and shared memory use. The hierarchy information is encoded into the grid
itself, reducing the memory overhead. Benchmarks show that in certain scenarios
the differences in deflections introduced by sampling the magnetic field model
can be significantly reduced when using the multiresolution approach.
