gCentroid shifting centroid towards concentration of points

Question

I have a SpatialPointsDataFrame defining SD boundary, however when I compute the center with gCentroid it's shifted.

c. = rgeos::gCentroid(c.) %>% as.data.frame()

Why isn't it plotting it at the center?

Gimlet

if you apply gCentroid to the bounding box does it still plot like that? – Taffrail

good idea, let me try – Gimlet

however, the draw back of finding the centroid of the bounding box is that it won't be very well placed for 'strangely' shaped polygons – Gimlet

Answer 1

It is because the mass of points is higher in the lower right corner. If you transform your object to a SpatialPolygons object (making it one shape) then it works:

poly <- SpatialPolygons(Srl = list(Polygons( srl = list(Polygon(coords = coordinates(dat))), ID = 1)))
gCentroid(spgeom = poly)

plot(poly)
axis(1)
axis(2)
points(gCentroid(poly)) 

Td