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

[Edzer Pebesma]

Well, they're called first and second, and a bit later they're named 
"left" and "right", it nowhere says that "left" is first, or second.

As you say, there's little point in making the distinction anyway; give 
me a case where it is confusing and I'll change it.
--
Edzer

Mark Connolly wrote:
> 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?
>>>
>>
>
>

-- 
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