I need to extract the vertices coordinates of the four corners of each rectangle of a layer made up of 729 polygons (= map sheets). I began using Vector/Geometry Tools/Extract Vertices function to create a vertices layer but each rectangle contains 7 vertices - the first and the last are superimposed, I suppose - so I want to eliminate the median vertices and one of the two (the first or the last) vertices superimposed. Moreover the 4 vertices of each rectangle coincide with the vertices of the adjacent rectangles having the same coordinates but different attributes related to the different map sheets.
Now I do not know how to delete the unwanted vertices (I can not use the Processing / Vector General / Delete Duplicate Geometries function because it would also delete the vertices of adjacent rectangles). How to solve this problem?
Extract Vertices
(see Ed Rollason's answer) on one of the polygon, and checkvertex_index
while clicking on each nodes. If you know the order it helps to distinguish which node corresponds to which corner.