Region's (area) viewshed using aspect peaks (RVAP or AVAP)

@Project: AVAP - Area Viewshed (Region's viewshed) using Aspect Peaks @Purpose: This script is for calculating a viewshed for an area instead of an observer point. It means that if the observer is placed anywhere on a given confined space (e.g. a polygon), which parts of the greater surface of the outside are still invisible to him or vice versa. With previous versions of viewshed, such a task was impossible due to a massive calculation time and other limitations. #Note: the final viewshed calculation needs Gdal>=3.1.0 but the rest could be run on lower versions.