Dear List,

I have a list of xy coordinates

> origin.point
[[1]]
           x         y
196 35.65648  4.268407
267 26.97161 -0.921370

[[2]]
            x         y
2396 25.82682 -34.30095
2485 24.36276 -31.83600
...

and I'm tryig to extract raster cell values within the radius like so:

cell.num <- unlist(xyValues(object = rst, xy = origin.point, buffer = 50))

For most coordinates, I get a list of vectors as expected, however, some
fail and produce only (one) NA. The raster serving as object is always the
same. For instance, in the list mentioned above, only coordinate 2 (
xy[[1]][2,]) in list 1 is causing such problems. I have tried rounding the
coordinates to no avail. Unfortunately I'm unable to reproduce the same
behavior outside my function. If I do it manually like so

cell.num1 <- unlist(xyValues(object = rst, xy = matrix(c(35.656483,
4.268407), nrow = 1, ncol = 2), buffer = 50)) #first coordinate

cell.num2 <- unlist(xyValues(object = rst, xy = matrix(c(26.97161,
-0.92137), nrow = 1, ncol = 2), buffer = 50)) #second coordinate

things go through without a problem.

This leads me to believe there is something in or around my custom function.
What is confusing me is the unpredictable behavior which makes it harder for
me to pinpoint the source where everything breaks. I tried following the
xyValues() but debugging S4 methods is not something I'm versed at (yet?!).
I have tried extracting xyValues() with

selectMethod(xyValues, c('RasterLayer', 'matrix'))

but the function calls even more internal functions and here is where I get
stuck.

I guess my questions are: what could be causing xyValues() to produce NA for
particular coordinates (but working fine with others) and - how to debug
xyValues() and it's internals like .xyvBuf, .readCells...? I would really
like to get to the bottom of this and move on.

Cheers,
Roman



-- 
In God we trust, all others bring data.

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