How to create circular polygon and add it to shapefile as a layer?

Question

I have such data of points which could be stored with their radii.

cdf = rbind(matrix(c(100, 200, 10), ncol = 3), matrix(c(400, 300, 20), ncol = 3))
di = c("1", "2")

spcs <- list()
for (c in 1:dim(cdf)[1]) {
  spc <- spCircle(radius = cdf[c,3], centerPoint = c(x=cdf[c,1], y=cdf[c,2]), spID = di[c])
  spcs <- c(spcs, spc)
}

Now, how to add it as a polygon (as other "normal" polygons) to the whole processing of creation of shapefile layers?

I do with typical polygons this way:

sps <- SpatialPolygons(spcs)
sdf <- SpatialPolygonsDataFrame(sps, data.frame(x = rep(NA, length(sps)), row.names = di))

rgdal::writeOGR(obj = sdf, dsn = title, layer = name, 
                  driver = "ESRI Shapefile", overwrite_layer = FALSE, verbose = TRUE)

but here the format is not the same. For example:

Error in SpatialPolygons(spcs) : no slot of name "area" for this object of class "SpatialPolygons"

How to add it as polygon

Answer 1

If you read the documentation for spCircle, specifically the Value section:

    Value:

         A list with the following components...

    spCircle : The "‘SpatialPolygons’" polygon object.

    location : The "‘SpatialPoints’" point object.

you'll see it returns a list with two components. It looks like you want the polygon object. In your loop make a list with just the spc$spCircle component instead of the entire spc object:

> spcs <- list()
> for (c in 1:dim(cdf)[1]) {
   spc <- spCircle(radius = cdf[c,3], centerPoint = c(x=cdf[c,1], y=cdf[c,2]), spID = di[c])
   spcs <- c(spcs, spc$spCircle)
 }

Now spcs a list of 2 SpatialPolygons objects each of length 1. To combine them into a SpatialPolygonsDataFrame with two rows you first have to row-bind them into a single SpatialPolygons object of length 2. Then you can SpatialPolygonsDataFrame them with some attributes:

> SpatialPolygonsDataFrame(do.call(rbind,spcs),data.frame(id=1:2,cdf))
class       : SpatialPolygonsDataFrame 
features    : 2 
extent      : 90.00503, 420, 190.0013, 319.9975  (xmin, xmax, ymin, ymax)
crs         : NA 
variables   : 4
names       : id,  X1,  X2, X3 
min values  :  1, 100, 200, 10 
max values  :  2, 400, 300, 20