Message-ID: <CAG4NReLNe1J9t=XBUot3ZMVdtS8-4dRT3wDt2qBOd0LUAxEXbA@mail.gmail.com>
Date: 2012-01-30T08:48:55Z
From: Agustin Lobo
Subject: Different result from sptransform() and ptransform()
In-Reply-To: <alpine.LRH.2.02.1201291946140.32011@reclus.nhh.no>
Roger,
While the explanation of the error is clear, I am actually not sure
about the practical consequences.
What I understand is that we must not use ptransform() by now (and use
spTransform() instead), and
that ptransform() will be fixed in the future. Am I right?
Thanks
Agus
2012/1/29 Roger Bivand <Roger.Bivand at nhh.no>:
> On Sat, 28 Jan 2012, Agustin Lobo wrote:
>
>> Right, grid1km is the polygon object from whence cents comes from and
>> I copied the wrong line.
>> Sorry for the confusion.
>
>
> The confusion is in proj4 in the ptransform() function, as:
>
>
>> centslonlat<- spTransform(cents,CRS("+init=epsg:4326"))
>> coordinates(centslonlat)[1:3,]
>
> ? ? ? ? ? ?X ? ? ? ?Y
> [1,] 1.315311 42.23956
> [2,] 1.327326 42.24060
> [3,] 1.339342 42.24163
>>
>> ptransform(data = coordinates(cents),
>
> ?src.proj = CRSargs(CRS("+init=epsg:3035")),
> ?dst.proj = "+proj=longlat +ellps=WGS84 +datum=WGS84"
> ?)[1:3,]*57.29577951308232
> ? ? ? ? [,1] ? ? [,2] [,3]
> [1,] 1.315311 42.23956 ? ?0
> [2,] 1.327326 42.24060 ? ?0
> [3,] 1.339342 42.24163 ? ?0
>
> ptransform() omits to test for geographical coordinates in the dst.proj=
> argument, and consequently does not multiply by RAD_TO_DEG. The correct code
> is in rgdal/src/projectit.cpp, from line 255. ptransform() is more recent
> than project() in proj4, so the fact that it isn't the same (either source
> or destination as longlat) got overlooked.
>
> Hope this clarifies,
>
> Roger
>