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I have a 500m sinusoidal raster that I converted it into an approximately equivalent 500m WGS84 using the raster package in R by using the following script:

library (raster)
library(maptools)
#Load the tif file
TIF <- raster("~/TIF.tif")
plot(TIF)
# Define the SRS of the original tif
SRS <- "+proj=sinu +lan_0=0 +x_0=0 +y_0=0 +R=631007.181 +units=m +no_defs"
#Define the Lat/Long SRS of the output Tif in WGS84
llcrs <- "+proj=longlat +ellps=WGS84 +datum=WGS84"
#Load original tif data
df <- as.data.frame(TIF, xy=TRUE)
#Define Transform
rll <- projectRaster(TIF,crs = llcrs)
#ras_sinu <- raster(nrow=391, ncol=695, ext=extent(-9031818, 4773511, -870816, 4954666), crs=incrs)
#rs <- rasterImage(w, ras_sinu)
plot(rll)
WGS84 <- raster("~/WGS84.tif")
plot(WGS84)

Next I checked whether the number of rows and columns match or not?

 summary(values(TIF))
 Min. 1st Qu.  Median    Mean 3rd Qu.    Max.    NA's 
 0.0    25.0    50.0    50.5    75.0   100.0  230368 
summary(values(WGS84))
Min. 1st Qu.  Median    Mean 3rd Qu.    Max.    NA's 
    0.0    26.0    51.0    50.5    76.0   100.0  454803 

table(is.na(match(values(TIF),values(WGS84))))
FALSE 
271745 
ncell(TIF)
271745
ncell(WGS84) 
496125
ncell(TIF) - ncell(WGS84)
-224380
sum(is.na(TIF[])) - sum(is.na(WGS84[]))
-224435
res(TIF)
463.3127 463.3127
res(WGS84)
0.00577 0.00417

I was checking answers to similar questions and it was mentioned after reprojections, the number of pixels change, hence that is why I am seeing a difference between the two rasters. This I guess means that the resolution of both the rasters is different as well. Is there a way in R to resolve this issue in R (i.e. the reprojected raster in WGS84 has a resolution approximate to 500m)?

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  • Can I use resample(0.009, 0.0045, method="bilinear", filename="", ...) in the raster package in R to get an approximate 500 m raster in Geographic coordinates? Bilinear method because the values of the raster are from 0-100 – Arthur_Morgan Oct 17 '20 at 0:05

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