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

[Dominik Schneider]

Hi Chris,
Thanks for confirming this. I'm not surprised that gdalUtils gives the same
answer as the gdal utilities - my understanding is that gdalUtils is
basically the equivalent to calling the commandline utilities via system().
I'm hoping that someone can shed light on spTransform since I use that a
lot for transforming points and polygons.
ds


On Mon, Feb 15, 2016 at 2:50 PM, Chris Reudenbach <reudenbach at uni-marburg.de
> wrote:

> 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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>>
>

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