[R-sig-Geo] Strange lines when projecting a world map

[Francesco Carotenuto]

Dear list, as in
the title, I found that when projecting a world map by mollweide projection and
setting a  longitude value, some strange
parallels are drawn. The real problem is that these lines “interact” with a
raster when performing the “over” function.
How can I manage
it?
Here I provide a
simulated example to let you understand what I mean
Thanks. 


#Example of a
world map mollweide projection with a specific longitude value
library(sp)
library(maptools)
library(rgdal)
data(wrld_simpl)
w_pol<-wrld_simpl
w_pol<-spTransform(w_pol,
CRS("+proj=moll +lon_0=66"))
plot(w_pol)
 
# Intersecting a
grid with the projected world map
gr<-expand.grid(x
= seq(-180, 180, length.out = 100), y = seq(-90, 90, length.out = 100))
coordinates(gr)<-~x+y
proj4string(gr)<-CRS("+proj=longlat
+ellps=WGS84 +datum=WGS84 +no_defs")
gr<-spTransform(gr,
CRS("+proj=moll +lon_0=66"))
plot(gr[w_pol,])
 

 
Dr. Francesco Carotenuto (Ph.D.)
Department of Earth Sciences
Federico II University
Largo S. Marcellino 10,
80138 NAPLES (ITALY)
http://francesco-carotenuto.blogspot.it/
http://3dpaleontology.blogspot.it/ 
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