[R-sig-Geo] different projection transformation R and gdal commandline

[Chris Reudenbach]

Hi Dominik,

If you use the gdalUtils package  there is no significant difference in 
the results using CLI or  R:

library(gdalUtils)
gdaltransform(s_srs="+proj=longlat +datum=WGS84", t_srs="+proj=lcc 
+lat_1=28 +lat_2=50 +lat_0=39.70001220694445 +lon_0=-98 +x_0=0 +y_0=0  
+ellps=sphere  +a=6370000 +b=6370000 +units=m 
+no_defs",coords=matrix(c(-112.25,33.0), ncol = 2))
          [,1]      [,2] [,3]
[1,] -1306676 -629522.5    0


If I use  spTransform I can reproduce your results:


loc <- c(-112.25,33.0)
loc <- data.frame(matrix(unlist(loc), nrow=1, 
byrow=T),stringsAsFactors=FALSE)
colnames(loc)<-c("lon","lat")
coordinates(loc)<- ~lon+lat
proj4string(loc)<- CRS("+proj=longlat +datum=WGS84 +no_defs")
loc<-spTransform(loc,CRS('+proj=lcc +lat_1=28 +lat_2=50 
+lat_0=39.70001220694445 +lon_0=-98 +x_0=0 +y_0=0 +ellps=sphere 
+a=6370000 +b=6370000 +units=m +no_defs'))
loc at coords
        lon     lat
1 -1306471 -629424

I suggest to focus on the sptransform() function

cheers Chris

 > sessionInfo()
R version 3.2.3 (2015-12-10)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 14.04.3 LTS

locale:
  [1] LC_CTYPE=de_DE.UTF-8       LC_NUMERIC=C LC_TIME=de_DE.UTF-8        
LC_COLLATE=de_DE.UTF-8
  [5] LC_MONETARY=de_DE.UTF-8    LC_MESSAGES=de_DE.UTF-8 
LC_PAPER=de_DE.UTF-8       LC_NAME=C
  [9] LC_ADDRESS=C               LC_TELEPHONE=C 
LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods base

other attached packages:
[1] gdalUtils_2.0.1.7 raster_2.5-2      sp_1.2-2

loaded via a namespace (and not attached):
  [1] rgdal_1.1-3       tools_3.2.3       Rcpp_0.12.3 R.methodsS3_1.7.0 
codetools_0.2-14  grid_3.2.3
  [7] iterators_1.0.8   foreach_1.4.3     R.utils_2.2.0 
R.oo_1.19.0       lattice_0.20-33




Am 15.02.2016 um 21:37 schrieb Dominik Schneider:
> Hi,
> I'm struggling to use a custom projection. I am seeing differences with
> someone using python proj4 bindings and when I compared my R results with
> my commandline results I got even more confused. the coordinate
> transformation is different for the two different methods.
>
> could someone explain to me which one is wrong and why?
> Thanks
>
> R:
> e=c(-112.25,-104.125,33,43.75)
> box=as(extent(e),'SpatialPolygons')
> proj4string(box)='+proj=longlat +datum=WGS84'
> pstring='+proj=lcc +lat_1=28 +lat_2=50 +lat_0=39.70001220694445 +lon_0=-98
> +x_0=0 +y_0=0 +ellps=sphere +a=6370000 +b=6370000 +units=m +no_defs'
> xmin(spTransform(box,CRS(pstring)))
> ## [1] -1306471
> ymin(spTransform(box,CRS(pstring)))
> ## [1] -713442.3
>
> commandline:
> iMac:~ $ gdaltransform -s_srs "+proj=longlat +datum=WGS84" -t_srs
> "+proj=lcc +lat_1=28 +lat_2=50 +lat_0=39.70001220694445 +lon_0=-98 +x_0=0
> +y_0
> =0  +ellps=sphere  +a=6370000 +b=6370000 +units=m +no_defs"
> -112.25 33.
> -1306675.75472246 -629522.472322824 0
>
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>
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