[R-sig-Geo] [FORGED] circular spatial polygon

[Loïc Dutrieux]

This is also possible with rgeos

library(sp)
library(rgeos)

x <- 673593.21
y <- 673593.21

sp0 <- SpatialPoints(coords = data.frame(x=x, y=y),
                     proj4string = CRS('+proj=utm +zone=20 +south
+ellps=WGS84 +datum=WGS84 +units=m +no_defs'))
sp1 <- gBuffer(sp0, byid=TRUE, width = 15, quadsegs = 2)
plot(sp1)


Cheers,
Loïc

On 12/09/2017 16:57, Rolf Turner wrote:
> 
> On 13/09/17 08:48, Kátia Emidio wrote:
> 
>> Dear all,
>> My question is how to create a circular spatial polygon, with 8 arcs
>> of 45
>> degrees, and radius measuring 15m. Having in the centre point the UTM
>> coordinates, zone 20S.
>>
>> x= *673593.21*
>> y= *673593.21*
> 
> "Circular polygon" is a contradiction in terms.  If a shape is a polygon
> then it is *not* a circle.  (Of course in real life we use polygons with
> large numbers of sides to *approximate* circles.  But 8 is not large!)
> 
> You can create an octagon with the required centre and radius using
> *spatstat* via:
> 
>     oct <- disc(radius=15,centre=c(673593.21,673593.21),npoly=8)
> 
> Does that provide (at least a start on) what you want?
> 
> cheers,
> 
> Rolf Turner
>