I have a problem in computing the centroids of certain polygons in QGIS (via the geometry tools): for certain polygons - with a strange and rather long shape - the centroids computed are off the polygon. Look, for instance, at the polygon marked in red, in the picture below:
Its centroid (pointed at by the blue arrow) is actually falling outside the polygon of interest. This occurs for a handful of (yet annoying) other polygons.
I am relatively new to QGIS, so I don't think whether this problem is due to the projection of the shapefile with the polygons (WGS 84). I tried anyway by re-projecting the map with WGS84/UTM Zone 31, which corresponds to Belgium (the country I'm looking at).