This dataset consists reprocessing and reformatting the SRTM30 PLUS v8.0 Digital Elevation Model (DEM) dataset developed by Scripps Institute Of Oceanography, University of California San Diego (UCSD) to produce a single raster covering the globe in GeoTiff format and create a full and low resolution hillshading from this DEM. The aim of this derived dataset is to reformat the data to allow easy use with GIS applications.
Full resolution hillshading:
The hillshading was produced by combining the 33 source DEMs using gdal_translate then processing using gdaldem with a z-factor of 0.0001. This output was then formatted as a JPEG compressed GeoTiff file with internal overviews (World_e-Atlas-UCSD_SRTM30-plus_v8_Hillshading.tif).
Low resolution smoothed hillshading:
A lower resolution of the hillshading (World_e-Atlas-UCSD_SRTM30-plus_v8_Hillshading-lr.tif) was also produced for for use when displaying zoomed out global maps. By making the hillshading smoother the bulk features (mountain ranges, etc) are easier to see.
This was generated by subsampling the DEM by two times (down to 21600x10800 pixels) then smoothing it with a pixel Gaussian filter. This was achieved using gdalwarp to subsample the data. Gdalbuildvrt was then used to create a virtual dataset that included a 4 pixel Gaussian filter kernel. The hillshading was then applied to this filtered data source using gdaldem with a z-factor of 0.0003, which 3 times stronger than the high resolution version of this dataset.
