4

I have a raster file where all pixels either are 0 (background) or 1 (see below, available at https://drive.google.com/file/d/1s2g8srXSTL6t-znF9nWbwK8f0C0K5FNk/view?usp=sharing).

I want R to find all regions of connected pixels and give them a unique ID. Then, I want to generate a shapefile via rasterToPolygons with one polygon for each region.
From what I can see, clump does the region grouping well. My code so far is:

test <- raster("C:/Users/.../sinks.tif")
regions <- clump(test)
regions_shp <- rasterToPolygons(regions, na.rm = T)

But that rasterToPolygons gives me a single polygon for every pixel and does not take into account the clump ID. What am I doing wrong?

enter image description here

3

You can use the dissolve argument, which dissolves all features with same value into polygon (or multi-polygon)

library(raster)

test <- raster("sinks.tif")
regions <- clump(test)
regions_shp <- rasterToPolygons(regions, na.rm = T, dissolve = T)

regions_shp

result of regions_shp:

class       : SpatialPolygonsDataFrame 
features    : 887 
extent      : -1010199, -978803.9, -92699.52, -39895.62  (xmin, xmax, ymin, ymax)
crs         : +proj=aea +lat_1=25 +lat_2=50 +lat_0=37 +lon_0=87 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0 
variables   : 1
names       : clumps 
min values  :      1 
max values  :    887 
| improve this answer | |
  • thanks a lot, I was looking for that! – Florian Mlehliv Jan 27 at 10:48

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