Using wavelet transforms in 3d mapping

The Naval Research Laboratory's Digital Mapping, Charting and Geodesy Analysis Program is investigating the application of wavelet technology to terrain approximation in 3D mapping. The wavelet transform allows us to obtain the frequency content of gridded elevation data while retaining the spatial context. We use a 2D discrete wavelet transform (DWT) to reduce Digital Terrain Elevation Data to low and high frequency components. The low frequency components represent widespread fluctuations in terrain and over large areas give a very close approximation to the oriainal data set. Each application of a wavelet transform gives us a 75% reduction in the amount of data that must be displayed. A level 2, 2D DWT allows us to represent large amounts of terrain data with only 6.25% of the original data. A reverse transform on the reduced data set makes possible the restoration of any level up to the original data with only minor loss, making the application suitable for multi-resolution systems. This application is also ideal for time-critical applications. Processing 1,073,179 DTED elevations down to 67,304 takes approximately one-half second. Optimized triangulated irregular network algorithms are reported to require over 45 seconds for a similar sized data set. We describe the application of wavelet technology to Intemet-based 3D mapping. In addition to custom 2D maps that may consist of vector, raster and gridded data, users may generate 3D maps by area-of- interest.