# [R-sig-Geo] How to translate coordinates from cylindrical to a Lambert Azimuthal Equal Area Projection

Ivailo ubuntero.9161 at gmail.com
Tue Apr 23 22:45:34 CEST 2013

```On Tue, Apr 23, 2013 at 7:41 PM, Barry Rowlingson
<b.rowlingson at lancaster.ac.uk> wrote:
> Okay, maybe all you want to do is work out where your raster projects to?
...

Huge thanks, Barry! I haven't thought of the problem in this way, but
your approach is definitely more simple and practical than the one I
vaguely imagined ;-)

> (But as I keep banging on, your grid in epsg:3035 won't line up with
> lat-long lines in that box)
>
> The other thing you can do is use spTransform to work out where the
> four corners of your raster transform to.

Yes, having read further to find a way solving my problem I realized
that both grids won't match exactly! Your example demonstrated that
quite succinctly; now I'll be careful while selecting the corners of
the possible extent as planned (in GE)...

> This corners function gets the four corner coordinates of a raster:
>
> corners <- function(r){
>   e = extent(r)
>   x=c(xmin(e),xmin(e),xmax(e),xmax(e))
>   y=c(ymin(e),ymax(e),ymin(e),ymax(e))
>   SpatialPoints(data.frame(x=x,y=y),proj4string=CRS(projection(r)))
> }
>
> and returns a SpatialPoints object in the original coordinate system:
>
>  > corners(re)
> SpatialPoints:
>            x       y
> [1,] 3577016 3714447
> [2,] 3577016 3827378
> [3,] 3654874 3714447
> [4,] 3654874 3827378
> Coordinate Reference System (CRS) arguments: +init=epsg:3035 +proj=laea
> +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m
> +no_defs
>
> Let's see where these transform to:
>
>  > spTransform(corners(re),CRS("+init=epsg:4326"))
> SpatialPoints:
>              x        y
> [1,] -1.972778 55.97462
> [2,] -2.290917 56.97278
> [3,] -0.738697 56.08479
> [4,] -1.025412 57.08626
> Coordinate Reference System (CRS) arguments: +init=epsg:4326
> +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0
>
> Useful?

Super useful, indeed -- thanks again for your great input, Barry!

Cheers,
Ivailo
--
UBUNTU: a person is a person through other persons.

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