I created polygons from a raster on which I ran an edge detection filter. I turned the edges into a polygon layer (multipart splitted into single parts). The intention was to have circular polygons at the end, but now there many single polygons forming one circle but are not touching each other, so I cannot connect these. The single yellow polygon in the figure below is an example.
Can anybody tell me how to connect all polygons in order to form a circle? The polygon is available as a download here. I work in SAGA, GRASS, or QGIS, or in R.