Projection issue with Zoogeographic Realms maps
The bounding box of your data is:
bbox(newRealms)
min max x -180.00000 180.0000 y -55.90223 83.6236 and since -180 is the same longitude as +180, its a coin toss as to what side of the world the projection will end up putting it on (well, not really a coin toss but subject to the approximations of floating point arithmetic and rounding). So any feature that has any point near + or - 180 has a chance of those points being mapped to the other side of the world on the Mollweide projection. This doesn't happen with the lat-long projection because +180 and -180 are stored separately and treated as those numbers without any transformation. Only once you start computing on those numbers (taking sines and cosines, for example) will you get into trouble. This may be the same problem as here: http://r-sig-geo.2731867.n2.nabble.com/Strange-lines-when-projecting-a-world-map-td7585274.html the solution might be to clip the original at -179 and +179 - that should keep points far enough away from the limb of the Mollweide projection. On Wed, Jul 16, 2014 at 8:45 PM, Daniel Varaj?o de Latorre
<danielvdelatorre at gmail.com> wrote:
Dear list, I am trying to change the projection of a SpatialPolygonsDataFrame but there is something wrong going on that I can't figure. The projected map show some lines that shouldn't be there. The shape file was downloaded from here: http://macroecology.ku.dk/resources/wallace/#Gis Here is the very simple code I'm using: setwd(PATH) newrealms<-readShapePoly("newRealms.shp") proj4string(newrealms) <- CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs") moll_crs<-CRS("+proj=moll +ellps=WGS84") newrealms_moll <- spTransform(newrealms, moll_crs) plot(newrealms) plot(newrealms_moll) #unexpected lines Can anyone help me with this? Thanks in advance! Daniel [[alternative HTML version deleted]]
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo