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

[Mark Connolly]

Thanks.  That works better.

It looks as though the documentation has left and right (implicitly) 
switched?  I am drawing line segments in 3D space using rgl, and I don't 
care so much about the order.  Might be confusing in some cases.


On 02/28/2010 09:49 AM, Edzer Pebesma wrote:
> 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?
>>
>


-- 
Graduate Student, Master of Science
Department of Soil Science
North Carolina State University