[R-sig-Geo] Question concerning calc() function in raster

[Robert J. Hijmans]

Hi Rainer,

1) .calcLayers is only used for functions that operate on a matrix;
not in other cases. Perhaps calc does not work correctly in some cases
(for some functions), and to investigate that it would be useful to
know what you are trying to accomplish.

2) yes that was wrong and now fixed. Thanks!

Best,
Robert


On Sun, Oct 10, 2010 at 11:43 AM, Rainer M Krug <r.m.krug at gmail.com> wrote:
> Hi
> I have two questions concerning the function calc() (more accurately
> .calcLayers()) (I append the code of the function below) :
> 1) The value given to the function fun() is a matrix, containig the values
> for many calls from all layers - this is not clear from the help page, and
> probably should be changed as it complicates the development of fun()
> functions. It effectively assumes, that the function fun() does vectorize
> the input parameter, which is in most cases when more complicated
> calculations are done, not the case (at least not for me). I would suggest
> to put it up to discussion, if this behaviour should be changed.
> 2) Is the (!canProcessInMemory(x, 2)) correct? I would actually assume, that
> the processing in one piece is only done, when canProcessInMemory() is
> TRUE?
> Cheers and thanks a lot for this really hice package (I am back and using it
> again),
> Rainer
>
> .calcLayers <- function(x, fun, filename='', ...) {
> filename <- trim(filename)
> outraster <- brick(x, values=FALSE)
> if (!canProcessInMemory(x, 2)) {
> v <- t( fun( t( getValues(x) )) )
> if (filename != '') {
> outraster <- writeRaster(outraster)
> }
> return( setValues(outraster, v) )
> }
> if ( filename == '') {
> filename <- rasterTmpFile()
> }
> outraster <- writeStart(outraster, filename=filename, ...)
> tr <- blockSize(outraster)
> pb <- pbCreate(tr$n, type=.progress(...))
> for (i in 1:tr$n) {
> sv <- t( fun( t( getValues(x, row=tr$row[i], nrows=tr$nrows[i]) )) )
> outraster <- writeValues(outraster, sv, tr$row[i])
> pbStep(pb)
> }
> outraster <- writeStop(outraster)
> pbClose(pb)
> return(outraster)
> }
>
> --
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>
> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation Biology,
> UCT), Dipl. Phys. (Germany)
>
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>
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>