distances values from a point exhibit a hexagon-like distribution

Can someone explain to me why values of distances from a point are not in a
uniform, circle-like fashion, but rather form a hexagon shape (see
image<http://imagepaste.nullnetwork.net/viewimage.php?id=1075>)?
Here is the code I'm using to produce this plot (kudos to
Robert<http://r-sig-geo.2731867.n2.nabble.com/assigning-raster-cell-values-based-on-predefined-criteria-td4929775.html#a4929775>).
Raster projection is "+projs = NA".

rst.poly <- polygonsToRaster(circle.polygon, rst) #circle.polygon is the
polygon I'm overlaying, rst is the raster
rst.lines <- linesToRaster(circle.polygon, rst)
rst.lines[rst.lines > 0] <- 0
rst.point <- pointsToRaster(rst, xy[[i]][j,]) #xy is the point from where
the distances are calculated
rst.cover <- cover(rst.point, rst.lines)
rst.grid <- gridDistance(rst.cover)
rst.grid[!is.na(rst.lines)] <- NA
plot(rst.grid)


Cheers,
Roman


--
In God we trust, all others bring data.

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