R spatial project: Jamaica Bay Lidar

tile 25160

task 1:

Chose tile ‘25160’ for 2017 which was roughly 1/4 of the 2014 tile ‘18TWK970955’. Created two dtms using the tin algorithm from lidR package. Then clipped 2014 tile by extent of 2017 tile and subtracted the two to get my first deposition/erosion result tile. Unsure if the results are 100% correct, but using mapview and zooming out a little, I can see it is at least in the right projection area in line with the basemap.

#reference bounding box numbers from metadata havent used yet
bbox <- c(-74.257499, 40.491252, -73.698030, 40.916459)

t2_2017 <-readLAS('25160_2017.las')
t2_2017_lr <- filter_poi(t2_2017, ReturnNumber == NumberOfReturns)
# Majority water pixels are classified under 40, 41, 45 values(should be 9) so needs reclassifying before interpolation
t2_2017_lr <- classify_poi(t2_2017_lr, class = as.integer(9), poi = ~Classification %in% c(40, 41, 45))
writeLAS(t2_2017_lr, file = 't2_2017_lr.las')
t2_2017_tin <- rasterize_terrain(t2_2017_lr, res=1, algorithm=tin(),pkg = 'raster')
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writeRaster(t2_2017_tin,'t2_2017_tin.tif', overwrite=TRUE)

t2_2014 <-readLAS('18TWK970955_2014.las')

t2_2014_lr <- filter_poi(t2_2014, ReturnNumber == NumberOfReturns)
st_crs(t2_2014_lr) <- 6347
# couldn't find proper projection for 2017 las data, 6347 just happened to line up w basemap and 2017 data, but wasn't correct crs code
writeLAS(t2_2014_lr, file = 't2_2014_lr.las')
t2_2014_tin <- rasterize_terrain(t2_2014_lr, res=1, algorithm=tin(), pkg= 'raster')
writeRaster(t2_2014_tin,'t2_2014_tin.tif', overwrite=TRUE)

#needed to crop 2014 to the extent of 2017, 2014 tile was larger
#project tin crs to match 2017 tin crs
t2_2014_tin2 <- projectRaster(t2_2014_tin, crs= crs(t2_2017_tin))
t2_2014_tin2 <- crop(t2_2014_tin2, t2_2017_tin)
#extents weren't perfectly matched up between 2014/2017 tins so had to resample
t2_2014_tin2 <- resample(t2_2014_tin2, t2_2017_tin, method = "bilinear")
writeRaster(t2_2014_tin2,'t2_2014_tin_cropped.tif', overwrite=TRUE)

# create the deposition/erosion layer from raster map algebra subtraction
t2_tin_depo <- t2_2017_tin - t2_2014_tin2
writeRaster(t2_tin_depo,'t2_tin_depo.tif', overwrite=TRUE)

#simple mapview plot of output tile
t2_tin_depo %>% mapview()