Hi,
My first advise is to point you to the vignette about "handling
shape les in the spatstat package" .Go to section 3.2.5 "Objects of
class SpatialPolygons".
In short, you could do something like this:
BaltCity2<-readShapePoly("baltcity_mdsp83m.shp")
play2<-ppp(play$X_m,play$Y_m, window=as.owin(BaltCity2))
...if you want to combine all polygons inside baltcity_mdsp83m.shp in
just one window. See the section section 3.2.5 "Objects of class
SpatialPolygons" for the other option (having different windows from
each indiviual polygon).
As you can see, I also removed the "meter to miles" conversion because
it's unnecesary if both the shapes and the play$X_m and play$Y_m
coordinates are in the same units (metres)
HTH,
Marcelino
El 07/03/2013 4:51, Abby Rudolph escribió:
Hi,
I was given the following code to determine whether the spatial distribution of
attribute=1 is significantly different from the spatial distribution of
attribute=0
given that the points (overall) are not randomly distributed in space.
BaltCity2<-readShapePoly("baltcity_mdsp83m.shp")
summary(BaltCity2)
x<-BaltCity2@polygons[[1]]@Polygons
x
summary(x)
# this shows that the baltimore polygon is a single shape
# the Baltimore shapefile is projected in meters, so the following code
converts meters to miles
coords<-slot(x[[1]],"coords")
coords<-coords[167:1,]
coords<-coords[-1,]
coords.mi<-coords*0.000621371192
summary(coords.mi)
play2<-ppp(play$X_m*0.000621371192,play$Y_m*0.000621371192,
window=owin(poly=list(x=coords.mi[,1],y=coords.mi[,2])))
I am able to get the program to work when I use the Baltimore shapefile because
the polygon is a single shape.
However, when I apply this code to data I have collected from New York City, I
have problems. I am wondering if the problem is the result of the NYC
shapefile having multiple polygons and water gaps. I have been attempting this
code with two different NYC shapefiles. The first is from NYC Bytes. I
brought it into ArcMap and projected it into meters.
When I plot the following in R, the points from my data file map onto the
shapefile and both are in meters
plot(NYCBB)
u<-RDS_TSO$RDS_new==0
points(RDS_TSOm$X_m[u],RDS_TSOm$Y_m[u],pch=5,col="yellow")
points(RDS_TSOm$X_m[!u],RDS_TSOm$Y_m[!u],pch=5,col="red")
However, when I use the code below to convert the meters to miles:
x<-NYBorough@polygons[[1]]@Polygons
x
# there are 8910 rows in x
summary(x)
# x is 5 different shapes compared to one like in the baltimore example above
Length Class Mode
[1,] 1 Polygon S4
[2,] 1 Polygon S4
[3,] 1 Polygon S4
[4,] 1 Polygon S4
[5,] 1 Polygon S4
coords<-slot(x[[1]],"coords")
coords
# Now there are only 47 rows - with the baltimore data there was no reduction -
I suspect it is being limited in some way
coords<-coords[19:1,]
coords
coords<-coords[-1,]
coords
NYBorough.coords.mi<-coords*0.000621371192
NYBorough.coords.mi
then, when I try to convert my data x,y coordinates from meters to miles and
create a shape with the NYBorough owin, I get a warning that all of the points
fall outside the window
RDS<-ppp(RDS_TSOm$X_m[u]*0.000621371192,RDS_TSOm$Y_m[u]*0.000621371192,
window=owin(poly=list(x=NYBorough.coords.mi[,1],y=NYBorough.coords.mi[,2])))
I received the following warning:
Warning message:
In ppp(RDS_TSOm$X_m[u] * 0.000621371192, RDS_TSOm$Y_m[u] * 0.000621371192, :
217 points were rejected as lying outside the specified window
This is puzzling, because when they are plotted using the following code, they
overlap
plot(NYBorough)
points(RDS_TSOm$X_m[u],RDS_TSOm$Y_m[u],pch=5,col="yellow")
and there are only 217 points in this group, so it appears that they are all
rejected.
I've also tried downloading the TIGER files from the US Census and merging all
5 boroughs, projecting the data in arcmap into meters and opening in R.
I get the same warning with both shapefiles.
Does it seem like the error is resulting from the shapefile I am using or some
other error in the code?
Any help would be very much appreciated.
Thanks!
Abby
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Marcelino de la Cruz Rot
Depto. de Biología Vegetal
Universidad Politécnica de Madrid
Madrid, España
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