[R] Warning message with "projectRaster" (package "raster"): 'from' has no cell values

[David Winsemius]

> On Mar 12, 2016, at 11:27 AM, Marine Regis <marine.regis at hotmail.fr> wrote:
> 
> Hello,
> 
> 
> 
> I have two rasters with different resolution and projection.

Generally posting questions about spatial functions will get faster and better responses on the sig-geo mailing list:

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Otherwise it may take a few days for Roger Bivand to come around and do "clean up" by answering and then using his broom to whisk you over there.

-- 
David.
> 
> 
> 
>> r1
> 
> class       : RasterLayer
> 
> dimensions  : 2510, 5233, 13134830  (nrow, ncol, ncell)
> 
> resolution  : 56, 56  (x, y)
> 
> extent      : 503198, 796246, 4917498, 5058058  (xmin, xmax, ymin, ymax)
> 
> coord. ref. : +proj=utm +zone=18 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0
> 
> data source : in memory
> 
> names       : layer
> 
> values      : 1, 8  (min, max)
> 
> 
> 
>> r2
> 
> class       : RasterBrick
> 
> dimensions  : 3250, 6570, 21352500, 1  (nrow, ncol, ncell, nlayers)
> 
> resolution  : 30, 30  (x, y)
> 
> extent      : 265380.5, 462480.5, 4984457, 5081957  (xmin, xmax, ymin, ymax)
> 
> coord. ref. : +proj=tmerc +lat_0=0 +lon_0=-73.5 +k=0.9999 +x_0=304800 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
> 
> data source : H:\users\rast_temp.tif
> 
> names       : rast_temp
> 
> 
> 
> My objective is to merge the two rasters into a single raster. As the two rasters have different resolution and projection, I have used the function projectRaster (package raster) like this:
> 
> 
> r <- projectRaster(from=r1, to=r2, method="ngb", alignOnly=TRUE)
> 
> 
> 
> However, I got this warning message:
> 
> 
> 
> Warning message:
> 
> In projectRaster(x, crs = projection(y)) : 'from' has no cell values
> 
> 
> 
> and yet, the two rasters have values:
> 
> 
> 
>> hasValues(r1)
> 
> [1] TRUE
> 
> 
> 
>> hasValues(r2)
> 
> [1] TRUE
> 
> 
> 
> When I remove the argument "alignOnly=TRUE", the code seems to work but I don't want that r1 has the same projected extent than r2 (I want to keep the original extent of r1).
> 
> 
> 
> Why do I get this warning message ?
> 
> 
> 
> Thank you very much for your help.
> 
> Marine
> 
> 
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> 
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David Winsemius
Alameda, CA, USA