Session 8 Code

Author

Carolyn Koehn

Playing with resolution:

Code

library(terra)

terra 1.7.78

Code

r <- rast(xmin=-4, xmax=9,
          ncols=10)
res(r)

[1] 1.3 1.0

Code

r2 <- rast(xmin=-4, xmax=9,
           resolution = c(1.3, 1))
ncol(r2)

[1] 10

Code

r3 <- rast(xmin=-4, xmax=5,
           ncols=10)
res(r3)

[1] 0.9 1.0

Code

empty_rast <- rast()

Practice questions

Code

# Question 1
rr <- rast(xmin=-5, xmax=5, ymin=-5, ymax=5, res=2)

# By looking at the help file, we realized that res overrides nrows/ncols
# This code uses the default global extent
rr2 <- rast(nrows=5, ncols=5, res=2)

Code

# Question 2
values(rr) <- runif(25)

# The "values were recycled" error clues us in that we don't have 25 cells
values(rr2) <- runif(25)

Warning: [setValues] values were recycled

Code

# Question 3
origin(rr)

[1] 1 1

Code

# Question 4
values(rr)[adjacent(rr, cells=12)] <- NA
plot(rr)

Code

# You can do this in two steps 
# by making an object to hold the adjacent cell numbers
adj <- adjacent(rr, cells=12)
values(rr)[adj] <- NA

For more information on subsetting, see the Software Carpentries R for Reproducible Data Analysis: Subsetting Data lesson.

Code

# Question 5
plot(distance(rr))


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Extra practice

To run examples of functions, go to the help file and scroll down to the “Examples” section. You can either copy-paste the code into your file or click the link that says “run examples.”

Code

# Question 2

fire_rast <- rast("/opt/data/data/assignment03/wildfire_hazard_agg.tif")
plot(distance(fire_rast))