SZIP

"SZIP is a utility for compressing data defined on the sphere.

Large data-sets that are measured or defined inherently on the sphere arise in a range of applications. Examples include, astronomical observations that are made on the celestial sphere, such as the cosmic microwave background (CMB) [see left image], and environmental illumination maps [see right image below] and reflectance functions used in computer graphics.

Technological advances in observational instrumentation and improvements in computing power are resulting in significant increases in the size of data-sets defined on the sphere. For example, current and forthcoming observations of the anisotropies of the CMB are of considerable size. Recent observations made by the NASA WMAP satellite contain approximately three mega-pixels, while the forthcoming ESA Planck mission will generate data-sets on the sphere with approximately fifty mega-pixels. The efficient and accurate compression of data on the sphere is therefore becoming increasingly important for both the dissemination and storage of data. 

SZIP was developed as a first step towards meeting these challenges. The compression algorithms implemented in SZIP are similar in flavour to JPEG 2000 compression of digital images. A wavelet transform (on the sphere) is applied as an energy compression stage, followed by entropy encoding. Further technical details are discussed below. SZIP is freely available for academic purposes and may be obtained by completing the download form below. We hope you enjoy SZIP and please get in contact if you have and requests for improvements in future versions.

SZIP provides an implementation of algorithms developed 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. Both lossless and lossy compression algorithms are included.  "

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