[R-sig-Geo] Reordering geographical coordinates clockwise to make a polygon

[Edzer Pebesma]

Look for argument check_ring_dir in the documentation of sf::st_read.

On 11/5/18 2:02 PM, Patrick Giraudoux wrote:
> Dear listers,
> 
> There is an interesting post here: 
> https://stackoverflow.com/questions/6989100/sort-points-in-clockwise-order 
> dealing on the issue. However, I would like to know if a function has 
> been already developped in a R package.
> 
> I am coping with a young colleague's shapefile where borders of polygons 
> have been drawn as lines quite inconsistently. To change this 
> SpatialLinesDataFrame into a SpatialPoints object is easy. The idea is 
> to  select the points  bordering each polygon (delete the others), 
> define the point set as a Polygon, then rebuild step by step a 
> SpatialPolygonsDataFrame with all its (~25) polygons. It would be much 
> quicker than to redraw one by one the 5160 data points (two times on 
> borders shared by two polygons).
> 
> The problem is that the points must be reordered clockwise (the way 
> lines making the  borders is all except clockwise) before making them a 
> polygon.
> 
> Any function already developped for that ?
> 
> Cheers,
> 
> Patrick
> 
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Edzer Pebesma
Institute for Geoinformatics
Heisenbergstrasse 2, 48151 Muenster, Germany
Phone: +49 251 8333081

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