Spatial Points to Polygons query-CodePudding

I have a question regarding converting spatial data in R and bringing it from R into QGIS.

I have a GeoTiff of Antarctic sea ice concentration, downloaded from the link below:

There are pink(s) interior to sic2 as these presumably are holes in sea ice that have the same value as northernmost contour that could perhaps be further removed by testing for within.

CodePudding user response：

I think this is what you are looking for.

library(terra)
r <- rast("asi-AMSR2-s3125-20221113-v5.4.tif")

# crop to the area of interest
e <- ext(-1975000, 1975000, 2e 05, 4350000)
re <- crop(r, e)

# get contour and save to file
v <- as.contour(re, levels=15)
writeVector(v, "contour_lines.shp")

Contours are normally lines (neither points nor polygons). But if you wanted a polygon you could do

x <- ifel(x <15 | x>100, NA, 1)
p <- as.polygons(x)
writeVector(p, "contour_polygons.shp")