Create square grids and export them as shapefile or table - r

Question

I would like to use the Google Earth Engine in order to extract data for certain countries. I need the data in the form of square grids, so I would like to create those square grids for a certain country, add them to the shapefile and then import the shapefile into the Earth Engine. I already found some code to create the square grids (Create a grid inside a shapefile), but now I have two problems.
First, I need to export the square grids so that I can import them to the Earth Engine. I'm very open to alternatives to the shapefile.
Second, the subsequent code works for some countries (like France), but not for others (like Thailand).
library(raster)
shp = getData(country = "FRA", level = 0)
shp = spTransform(shp, CRSobj = "+proj=utm +zone=32 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0")
plot(shp)
cs = c(10000, 10000)
grdpts = makegrid(shp, cellsize = cs)
spgrd = SpatialPoints(grdpts, proj4string = CRS(proj4string(shp)))
spgrdWithin = SpatialPixels(spgrd[shp,])
plot(spgrdWithin, add = T)
Replacing "FRA" by "THA" in line 2 leads to an error in spTransform.

Answer 1

That fails because you are using utm zone 32. You need to use the zone based on the longitude of the country. You can see them here
You can automate finding a zone with ceiling((longitude+180)/6)
library(raster)
s <- getData(country = "FRA", level = 0)
Get the centroid. In this case you can do
centr <- coordinates(s)
If there are multiple polygons, you can do something like this
centr <- apply(coordinates(s), 2, mean)
Compute the UTM zone. (note that you had 32 for France, which is not good)
zone <- ceiling((centr[1] + 180)/6)
zone
#[1] 31
And then use it like this
crs <- paste0("+proj=utm +datum=WGS84 +unit=m +zone=", zone)
st <- spTransform(s, crs)
For Thailand you would get
s <- getData(country = "THA", level = 0)
centr <- apply(coordinates(s), 2, mean)
zone <- ceiling((centr[1] + 180)/6)
zone
#[1] 47
However, this is not an approach that would work for all countries. UTM zones are 6 degrees wide, and many countries span multiple zones (Russia takes the cake with 28 zones). So depending on your goals, you may want to use another coordinate reference system (crs).
After that, an alternative way to get square polygons is to create a RasterLayer with the extent of s, and a resolution of choice. But I doubt that this is the best way to get data out of GEE. I would suggest uploading the country outline instead.
r <- raster(st, res=10000)
r <- rasterize(st, r, 1)
x <- as(r, "SpatialPolygons")
# write to file
shapefile(x, "test.shp")
# view
plot(x)