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.

@项目：AVAP——基于坡面峰值（Aspect Peaks）的区域视域（Region's viewshed）分析工具
@用途：本脚本用于计算区域级视域，而非单点观测者视域。具体而言，若将观测者置于指定受限空间（如多边形区域）内的任意位置，可分析外部更大范围地表中哪些区域无法被其观测到，反之亦然。过往版本的视域分析工具受限于海量计算耗时与其他技术约束，无法完成此类任务。
#注意：最终的视域计算环节需依赖GDAL（Geospatial Data Abstraction Library）3.1.0及以上版本，其余流程可在更低版本的运行环境中执行。