The service: Polygon ring cutout
This not (yet?) standardized extension to OGC WCS and WCPS allows
clipping against polygon provided in WKT (Well-Known Text) representation.
Polygons can self-intersect, and multi-polygons are possible (such as for areas with many lakes).
The clip() function operates along space and time,
it can alternatively discard the exterior or the interior.
The result of this WCPS query is a 2-D image considering only the polygon interior, overlaid on a base map.