Voids are points of the SRTM data tiles that contain no data, this happens to bad radar scatter and on some places such as the Alps, shown on the sample, the voids clearly disturb the terrain perception.
DG SRTM Void Killer works by mixing SRTM and GTOPO30 data, it detects a void (lack of elevation data) and then it gets the information of an user supplyed GTOPO30 tile.
before: after: As you can see the result is surprisingly fine, althought the poorest resolution of GTOPO30 data set, the terrain perception is anyway realistic, as you can see on a 3D view of the same area:Fig.
1 Correction using GTOPO Only. Fig. 2 Correction using SRTM Interpolation Only. Fig. 3 Correction using Both GTOPO and Interpolation. This simple method, is far more realistic and reliable than complicated interpolation methods that don`t use real terrain data to fill the voids, althought those techniques often make more rich; terrain rendering, voids distribution is not sparse, usually, as seen on this sample, voids often are grouped and cover a great area, this can understimate entire mountains!
DG-Void Killer uses GTOPO30 a world wide 1km real-terrain data to fill the voids, and any area will be recovered with much greater realism. Mixing both GTOPO30 Data Set and using Advanced Interpolation Techniques on the SRTM Tile, makes the terrain reliability great as well as the the look, for improved realism.