Compressing digital elevation models with wavelet decomposition

Wavelet decomposition is a well-known technique to compress image data. Here, we have used wavelet decomposition to compress digital elevation models, DEM. The objectives for compressing DEMs are obtaining manageable and small data sets, and reducing data access time. In the paper, different aspects of wavelets as a base for data compression are described. The (de-)compression scheme consists of three steps: wavelet decomposition, quantization, and de-/encoding. A few selected techniques to carry out these steps are presented here. Wavelet decomposition does not destruct or compress data. In the decomposition, data are re-organised in a way that facilitates compression. In the quantization step, data can be destructed. It is shown that the quantizer can be constructed to obtain high compression ratios and a low degree of destruction of data. An adaptive quantizer that considers the distribution of data gives the best result. Performance measures for the 50x50 m DEM of all of Sweden are presented.