spTransform: unable to convert coordinates

On Thu, 23 Aug 2012, Martin Ivanov wrote:

Dear Prof. Bivand,

Here is a minimal working example with SpatialLines and 
SpatialPolygons. With both objects spTransform does not
multiply the transformed coordinates by 180/pi:

crds1 <- matrix(data=c(7, 51, 8, 52, 9, 52, 10, 51), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds2 <- matrix(data=c(8, 48, 9, 49, 11, 49, 9, 48), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds3 <- matrix(data=c(6, 47, 6, 55, 15, 55, 15, 47), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
spLines <- SpatialLines(list(Lines(list(Line(crds1), Line(crds2), 
Line(crds3)), ID="a")));
spLines at proj4string <- CRS("+proj=longlat +ellps=sphere +no_defs");
bbox(spLines);
spLines_tr <- spTransform(spLines, CRS("+proj=ob_tran +o_proj=longlat 
+o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere +no_defs"), 
use_ob_tran=TRUE);
bbox(spLines_tr)
bbox(spLines_tr)*180/pi

crds1 <- matrix(data=c(7, 51, 8, 52, 9, 52, 10, 51, 7, 51), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds2 <- matrix(data=c(8, 48, 9, 49, 11, 49, 9, 48, 8, 48), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
crds3 <- matrix(data=c(6, 47, 6, 55, 15, 55, 15, 47, 6, 47), ncol=2, 
byrow=TRUE, dimnames=list(NULL, c("lon", "lat")));
spPolygons <- SpatialPolygons(list(Polygons(list(Polygon(crds1), 
Polygon(crds2), Polygon(crds3)), ID="a")));
spPolygons at proj4string <- CRS("+proj=longlat +ellps=sphere +no_defs");
bbox(spPolygons);
spPolygons_tr <- spTransform(spPolygons, CRS("+proj=ob_tran 
+o_proj=longlat +o_lon_p=-162 +o_lat_p=39.25 +lon_0=180 +ellps=sphere 
+no_defs"), use_ob_tran=TRUE);
bbox(spPolygons_tr)
bbox(spPolygons_tr)*180/pi


The correct bounding boxes are the second ones. Hence the coordinates 
have also got to be multiplied by 180/pi.

Please check R-forge revision 360 - the argument reversal was done 
correctly for points (so for pixels and grids), but the wrong way 
round for the other two cases. Test now in help page example.

Thanks for your patience,

Roger

Best regards,

Martin






On 08/23/2012 02:37 PM, Roger Bivand wrote:

On Thu, 23 Aug 2012, Martin Ivanov wrote:

Dear Prof. Bivand,

I tested spTransform with a SpatialLines object and it still does 
not multiply the coordinates by 180/pi. With SpatialPixels, 
SpatialPoints and SpatialGrids it works perfectly though. If 
necessary, I will provide a minimal working example.

Please do - I may have left something out. I'm travelling now, so an 
example would help. What about SpatialPolygons objects?

Roger

Best regards,