library(lidR)

library(sf)
## Linking to GEOS 3.11.0, GDAL 3.5.3, PROJ 9.1.0; sf_use_s2() is TRUE
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## Attaching package: 'sf'
## The following object is masked from 'package:lidR':
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library(sp)
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library(raster)
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##     projection, projection<-
library(terra)
## terra 1.7.71
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library(ggplot2)

library(mapview)

library(tidyverse)
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## ✔ dplyr     1.1.4     ✔ readr     2.1.5
## ✔ forcats   1.0.0     ✔ stringr   1.5.1
## ✔ lubridate 1.9.3     ✔ tibble    3.2.1
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## ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors

Read in tiles

las.data.2014 <- readLAS("/Users/jamesreo/Desktop/Blue Carbon Data/18TWK970955.las")

las.data.2017 <- readLAS("/Users/jamesreo/Desktop/Blue Carbon Data/25162.las")
## Warning: There are 6661036 points flagged 'withheld'.

Filter

filter.las.data.2014 <- filter_last(las.data.2014)

filter.las.data.2017 <- filter_last(las.data.2017)

#clean house to free storage 
rm(las.data.2014)

rm(las.data.2014)
## Warning in rm(las.data.2014): object 'las.data.2014' not found
#Original data for 2017 filtered data is too voluminus, classifying as per Andy's method allows for dsm creation

classified_2017 <- classify_poi(filter.las.data.2017, class = as.integer(9), poi = ~Classification %in% c(40, 41, 45))

Rasterize

dsm2014 <- rasterize_terrain(filter.las.data.2014, res=1, algorithm=tin(), pkg= 'raster')
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dsm2017 <- rasterize_terrain(classified_2017, res=1, algorithm=tin(), pkg= 'raster')
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crs(dsm2014) <- CRS("EPSG:6347")

dsm2014_reproject <- projectRaster(dsm2014, crs = crs(dsm2017))

Attempting to obtain a difference from the above dsm layers will result in an error due to uneven extents, I will attempt to extract by mask dsm2017 to match the extent of dsm2014

resample 2014 dsm to match 2017 grid cells

cropped_2014 <- crop(dsm2014_reproject,dsm2017, snap="near")

dsm2014.resample <- resample(cropped_2014,dsm2017, method="bilinear")

difference_dsm <- dsm2017- dsm2014.resample

writeRaster(dsm2014.resample, "dsm2014resamp2.tif", overwrite=TRUE)
writeRaster(dsm2017,'dsm2017.tif',overwrite=TRUE)
writeRaster(difference_dsm,'difference.tif',overwrite=TRUE)

mapview(difference_dsm)
## Warning in rasterCheckSize(x, maxpixels = maxpixels): maximum number of pixels for Raster* viewing is 5e+05 ; 
## the supplied Raster* has 6250000 
##  ... decreasing Raster* resolution to 5e+05 pixels
##  to view full resolution set 'maxpixels =  6250000 '