Question concerning calc() function in raster

Sun, Oct 10, 2010 10:07 AM

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,
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Question concerning calc() function in raster

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