lidR (version 1.6.1)

grid_catalog: Apply a grid function over a catalog

Description

This function applies over an entire catalog any user-defined function that returns a lasmetrics object. Used internaly by grid_metrics, grid_terrain, grid_canopy and other grid_* functions when the input is a LAScatalog, it ensures continuous rasterization of the dataset and performs pre- and post-processes. This function can be seen as a straightforward 'grid-specific' version of catalog_apply, which is even more generic.

Usage

grid_catalog(catalog, grid_func, res, select = "*", filter = "",
  start = c(0, 0), ...)

Arguments

catalog

A LAScatalog

grid_func

A function that returns a lasmetrics object. This function must follow a specific template (see details and examples)

res

numeric. Resolution of the grid

select

character. The 'select' parameter from readLAS.

filter

character. The 'filter' parameter from readLAS.

start

numeric. The 'start' parameter from grid_metrics

...

Any other parameter required by grid_func

Value

Returns a data.table containing the metrics for each cell. The table has the class "lasmetrics" enabling easy plotting.

Details

The user-defined function grid_func must respect a template. Like in grid_metrics, grid_terrain or grid_canopy, the user-defined function must have a parameter called x that will receive a LAS object and a parameter res that will receive the resolution of the grid. The parameter start is optional.

Examples

# NOT RUN {
# This example computes the mean elevation of points above 5 m over an entire
# catalog, after removing all points in lakes into a shapefile.

LASfile <- system.file("extdata", "Megaplot.laz", package="lidR")
shapefile_dir <- system.file("extdata", package = "lidR")

ctg = catalog(LASfile)
tiling_size(ctg) <- 160

lakes = rgdal::readOGR(shapefile_dir, "lake_polygons_UTM17")

my_grid_metrics = function(x, res, spdf)
{
  lasclassify(x, spdf, "inpoly")
  x = lasfilter(x, !inpoly)
  grid_metrics(x, mean(Z), res)
}

mean = grid_catalog(ctg, my_grid_metrics, 20,
                    select = "xyz", filter = "-drop_z_below 5",
                    spdf = lakes)

# }