2012/3/29 Roger Bivand <roger.biv...@nhh.no>
> On Thu, 29 Mar 2012, Raffaele Morelli wrote:
>
> Hi,
>>
>> I am working on a simple kernel2d analisys and would like to create a
>> polymap from a SpatialPolygonsDataFrame, let's stay US states.
>> how can I accomplish this task? can you point me to the right direction?
>>
>
> Why? Please include sample code. I assume that you realise that the poly=
> argument in this function requires a single polygon ring, so you would
> first have to define your window and go from there.
>
I have a SpatialPointsDataFrame all over Italy and I am calculating
kernel2d for each district (24 administrative boundaries, eg. Lazio,
Piemonte, Sicilia, Sardegna...)
# I fetch Italy boundaries and the spdf from postgres with:
districts <- readOGR("PG:dbname=xxxx host=xxx user=xxx password=xxx",
"italy_utm32")
points <- readOGR("PG:dbname=xxx host=xxx user=xxx password=xxx",
"points_utm32")
# I want to calculate kernel 2d for districts then the need to "extract"
the poly for EACH of them using administrative boundaries for poly
argument, so:
regione <- districts[districts$ditricts_id==cod,] # where cod is the
district id
# and then I solved the thread question using:
poly <- as.matrix(district@polygons[[1]]@Polygons[[1]]@coords)
plot(regione, asp=1)
image(kernel2d(as.points(points@coords), poly, h0=5000, nx=450, ny=450),
add=TRUE, col=terrain.colors(10))
plot(regione, lwd=3, border="grey50", add=TRUE, axes=TRUE)
I hope this is clear, apologize for my english :(
Actually I am facing with another issue. Each dictrict can have isles, so I
should guess the number of polygons object for each district
eg.
> str(district@polygons[[1]])
Formal class 'Polygons' [package "sp"] with 5 slots
..@ Polygons :List of 37
......
and I should calculate kernel2d for each isle.
So, how can I guess the list lenght (37 in the example above)?
I tried using
length(regione@polygons[[1]])
with no success...
regards
-r
--
*L'unica speranza di catarsi, ammesso che ne esista una, resta affidata
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