[R-sig-Geo] bug in process definition for retrieving point pair indexes from varigramCloud

[Edzer Pebesma]

Mark, the documentation falsely assumes all computers have 32 bits 
integers; yours seems not -- compare the .BigInt with sqrt(2^64). To see 
how the point pairs are obtained, look at:

 > gstat:::as.data.frame.variogramCloud
function (x, row.names, optional, ...)
{
    .BigInt = attr(x, ".BigInt")
    x$left = x$np%%.BigInt + 1
    x$right = x$np%/%.BigInt + 1
    x$np = NULL
    class(x) = "data.frame"
    x
}

so the .BigInt attribute is the divisor; 1 is added because the arrays 
are set up in the C code, starting at 0.
--
Edzer

Mark Connolly wrote:
> gstat reference states
>
> If cloud is TRUE: an object of class variogramCloud, with the field np 
> encoding the numbers of the point pair that contributed to a variogram 
> cloud estimate, as follows. The first point is found by the integer 
> division of np by 2^16, the second point by the remainder of that 
> division.
>
> For
> Classes ‘variogramCloud’ and 'data.frame': 3275 obs. of 6 variables:
> $ np : num 8.59e+09 8.00 8.59e+09 1.29e+10 1.29e+10 ...
> $ dist : num 18.8 79.2 77.8 78.7 100.1 ...
> $ gamma : num 0.781 0.845 12.903 5.611 0.344 ...
> $ dir.hor: num 0 0 0 0 0 0 0 0 0 0 ...
> $ dir.ver: num 0 0 0 0 0 0 0 0 0 0 ...
> $ id : Factor w/ 1 level "var1": 1 1 1 1 1 1 1 1 1 1 ...
> - attr(*, "direct")='data.frame': 1 obs. of 2 variables:
> ..$ id : Factor w/ 1 level "var1": 1
> ..$ is.direct: logi TRUE
> - attr(*, ".BigInt")= num 4.29e+09
>
>
> v[1,] yields:
> dist gamma dir.hor dir.ver id left right
> 1 18.75474 0.78125 0 0 var1 6 3
>
>
> v$np[1] %/% 2^16 yields:
> 131072
>
> Which is != 6
>
> Am I misinterpreting the documentation?
>

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster 
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251 
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de 
http://www.52north.org/geostatistics      e.pebesma at wwu.de