Hi Alexandre, it seems to me this is a job for function 'focal' rather then 'extract'. Even if so, I'm not sure about the speed it would take.
Cheers Hugo ASANTOS via R-sig-Geo <[email protected]> escreveu no dia domingo, 18/11/2018 à(s) 14:10: > Dear R-sig-geo Members, > > I've like to use R and raster package (extract() function) for > pixel calculations (SD, Skewness and Kurtosis in 1 unit radius of a > buffer) in a geoTiff raster, but my original geoTiff image has > 6244(nrow), 8721(ncol) and 54453924 (ncell) dimensions. This image size > causes slow computation process or computer lock, for example in my code > below: > > ### <code r> > #Packages > library(raster) > library(moments) #Measures of Skewness and Kurtosis > > ## Create artificial raster for my geoTiff simulation - dimensions of > my original geoTiff: 6244, 8721, 54453924 (nrow, ncol, ncell) > r <- raster(nc=8721, nr=6244) > r <- setValues(r, round(runif(ncell(r))* 255)) > > #Extract all pixel coordinates in raster > coord_r<-coordinates(r) > > #Extract standard deviation, skewness and kurtosis > Buffer<-1 > SD<-function (x, na.rm = TRUE) > { > if (is.matrix(x)) > apply(x, 2, sd, na.rm = na.rm) > else if (is.vector(x)) > sqrt(var(x, na.rm = na.rm)) > else if (is.data.frame(x)) > sapply(x, sd, na.rm = na.rm) > else sqrt(var(as.vector(x), na.rm = na.rm)) > } > desv_pad_R<-extract(r, coord_r, buffer = Buffer, fun = SD) > str(desv_pad_R) > sk_R <-extract(r,coord_r,buffer=Buffer, fun=skewness, na.rm = TRUE) > str(sk_R) > k_R <-extract(r,coord_r,buffer=Buffer, fun=kurtosis, na.rm = TRUE) > str(k_R) > # <END code> > > There are different approaches (eg. integration with SAGA GIS or > GRASS, convert image to ASCII) for my problem? > > Thanks in advanced, > > Alexandre > > -- > ====================================================================== > Alexandre dos Santos > Proteção Florestal > IFMT - Instituto Federal de Educação, Ciência e Tecnologia de Mato Grosso > Campus Cáceres > Caixa Postal 244 > Avenida dos Ramires, s/n > Bairro: Distrito Industrial > Cáceres - MT CEP: 78.200-000 > Fone: (+55) 65 99686-6970 (VIVO) (+55) 65 3221-2674 (FIXO) > > [email protected] > Lattes: http://lattes.cnpq.br/1360403201088680 > OrcID: orcid.org/0000-0001-8232-6722 > Researchgate: www.researchgate.net/profile/Alexandre_Santos10 > LinkedIn: br.linkedin.com/in/alexandre-dos-santos-87961635 > Mendeley:www.mendeley.com/profiles/alexandre-dos-santos6/ > > _______________________________________________ > R-sig-Geo mailing list > [email protected] > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
