Volume 531, July 2011
|Number of page(s)||13|
|Section||Numerical methods and codes|
|Published online||21 June 2011|
Data compression on the sphere
Institute of Electrical Engineering, Ecole Polytechnique Fédérale de
2 Astrophysics Group, Cavendish Laboratory, J. J. Thomson Avenue Cambridge, CB3 0HE, UK
3 Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
4 Department of Radiology and Medical Informatics, University of Geneva (UniGE), 1211 Geneva, Switzerland
5 Department of Computer Science, University of Otago, Dunedin 9016, New Zealand
6 University of Cambridge Computer Laboratory, J. J. Thomson Avenue, Cambridge CB3 0FD, UK
Accepted: 29 April 2011
Large data-sets defined on the sphere arise in many fields. In particular, recent and forthcoming observations of the anisotropies of the cosmic microwave background (CMB) made on the celestial sphere contain approximately three and fifty mega-pixels respectively. The compression of such data is therefore becoming increasingly important. We develop algorithms to compress data defined on the sphere. A Haar wavelet transform on the sphere is used as an energy compression stage to reduce the entropy of the data, followed by Huffman and run-length encoding stages. Lossless and lossy compression algorithms are developed. We evaluate compression performance on simulated CMB data, Earth topography data and environmental illumination maps used in computer graphics. The CMB data can be compressed to approximately 40% of its original size for essentially no loss to the cosmological information content of the data, and to approximately 20% if a small cosmological information loss is tolerated. For the topographic and illumination data compression ratios of approximately 40:1 can be achieved when a small degradation in quality is allowed. We make our SZIP program that implements these compression algorithms available publicly.
Key words: methods: numerical / cosmic background radiation
© ESO, 2011
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