Grid points within polygon: previous solution does not work for me

Question

For some reason I can't get the solution provided by @RichPauloo to work and do appreciate some help.

I have a SpatialPolygonsDataFrame called "spdf" (in the dropbox link below) https://www.dropbox.com/s/ibhp5mqbgfmmntz/spdf.Rda?dl=0

I used the code from below post to get the grid data within the boundary.

Create Grid in R for kriging in gstat

library(sp)
grd <- makegrid(spdf, n = 10000)

colnames(grd) <- c('x','y');

outline <- spdf@polygons[[1]]@Polygons[[1]]@coords

library(splancs)

new_grd <- grd[inout(grd,outline), ]

Here is what I get:

• Black dots are "grd" from makegrid

• Blue dots are "outline" as boundary

• Red dots are"new-grd" as the grid within the boundary

As you can see it does not capture all the data within the boundary? What am I doing wrong?

Answer 1

Try this:

# packages
library(sp)

# make grid
grd <- makegrid(spdf, n = 100)
colnames(grd) <- c('x','y') # assign names to columns

# check the class
class(grd)

# transform into spatial points
grd_pts <- SpatialPoints(coords = grd, 
                         proj4string=CRS(as.character(NA)))

# check the class again
class(grd_pts)

# show that points fall outside of polygon
plot(spdf)
points(grd_pts)

# subset for points within the polygon
grd_pts_in <- grd_pts[spdf, ]

# visualize
plot(spdf)
points(grd_pts_in)

# transform grd_pts_in back into a matrix and data frame
gm <- coordinates(grd_pts_in) # matrix
gdf <- as.data.frame(coordinates(grd_pts_in)) # data frame