Hello,

When I attempt to project polygons of the world's continents (from proj=longlat to proj=wag4), projection is successful using rgdal's -spTransform-

cont=readShapeSpatial("continents")

proj4string(cont)="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"

cont_proj=spTransform(cont,CRS("+proj=wag4 +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"))

But when I plot the projected spatial polygons, there are horizontal "scratches" stretching across the plot. They occur where polygons "wrap" around the xmin and xmax of the extent.

I have tried -nowrapRecenter- (maptools) prior to transformation (hoping it might "break" the polygons producing the error), but it doesn't seem to solve the issue. Package "maps" has a 'wrap' argument that I notice eliminates this problem when plotting, but there are not enough projections available for me to use that package.

This doesn't seem like an exotic problem, so I'm sure someone has dealt with it before...

Thanks in advance,
Kevin

Kevin Ummel
Senior Visiting Associate, Center for Global Development
MESPOM Candidate, University of Manchester





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