Draw a polygon over PNG image R

Question

I have a PNG image wich I have opened in R and in order to give coordinations converted into a SpatRast object with the following code:

library(terra)
r <- rast("yanomamis.png")
#Warning: [rast] unknown extent

## drop the alpha channel 
r <- r[[1:3]]
## declare the R,G,B channels
RGB(r) <- 1:3
ext(r) <- c( -70.18066, -55.6897, -0.5009, 4.89839 )
crs(r) <- "+proj=longlat +datum=WGS84" 

Which resulted in:

r
#class       : SpatRaster 
#dimensions  : 503, 1328, 3  (nrow, ncol, nlyr)
#resolution  : 0.01091187, 0.01073417  (x, y)
#extent      : -70.18066, -55.6897, -0.5009, 4.89839  (xmin, xmax, ymin, ymax)
#coord. ref. : +proj=longlat +datum=WGS84 +no_defs  
#source      : yanomamis.png 
#colors RGB  : 1, 2, 3 
#names       : yanomamis_1, yanomamis_2, yanomamis_3 

My goal is to draw over this plot and save the drawing as a shape file, which I thought I could accomplish with the function draw from the terra package.

However, when I try to execute the code, Im not able to draw anything over the plot.

Can anyone see what am I missing?

Answer 1

To be able to draw on a map in R-Studio, it needs to be plotted in the plot window.

Since you are using a ".Rmd" (Rmarkdown) file, you need to select "Chunk Output in Console" (select the "gear" menu next to "knitr" menu).

An Rmarkdown file seems an odd choice if you are looking for this type of interaction. You could use a simple R code (".R") file instead. Or you could run plot(r) in the R console.