CODEWITHSUNDEEP
rgeospatialpolygonspatialr-raster
Tani
Tani

Reputation: 1

How do I calculate the shortest distance between a spatial point and a raster grid cell of a certain value?

I have a spatial points file which has a list of coordinates for sample sites. I need to find how close each of these sample sites is to highly human-modified areas. I'm using the global human modification index (https://sedac.ciesin.columbia.edu/data/set/lulc-human-modification-terrestrial-systems), which is in raster format. For each point (sample site), I need to find the shortest distance to the nearest raster grid cell that has a value > 0.7. Is there a way in R to select the nearest grid cell with a value > 0.7 and then calculate the distance between this (probably the central point of the cell?) and my other points?

I have too many sites to calculate the distance manually.

So, my final dataframe would have a column for site number, latitude, longitude, and distance to high human modification.

I may opening a whole other can of worms by saying that I preferably need the distance in km - can I do this by converting the CRS of my points and raster to UTM with units=m first?

Thanks in advance!

Upvotes: 0

Views: 402

Answers (1)

Yelle Vosteen
Yelle Vosteen

Reputation: 1

I created a vector out of the specific values of the raster and applied the distance() to that so:

# Extract the values larger than 0.7 from the raster
value_lt <- ifel(cell_value >0.7 ,1, NA)

# Convert to a polygon
value_lt_sf <- value_lt %>%
  as.polygons()

# calculate distance of points to the polygon
dist_to_value <- distance(points, value_lt_sf)

Upvotes: 0

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