The Local Maximum stage identifies points that are locally maximum. The window size is
fixed and circular. This stage does not modify the point cloud. It produces a derived product
in vector format. The function local_maximum_raster applies on a raster instead of the point cloud
Arguments
- ws
numeric. Diameter of the moving window used to detect the local maxima in the units of the input data (usually meters).
- min_height
numeric. Minimum height of a local maximum. Threshold below which a point cannot be a local maximum. Default is 2.
- filter
the 'filter' argument allows filtering of the point-cloud to work with points of interest. For a given stage when a filter is applied, only the points that meet the criteria are processed. The most common strings are
Classification == 2","Z > 2","Intensity < 100". For more details see filters.- ofile
character. Full outputs are always stored on disk. If
ofile = ""then the stage will not store the result on disk and will return nothing. It will however hold partial output results temporarily in memory. This is useful for stage that are only intermediate stage.- use_attribute
character. Specifies the attribute to use for the operation, with "Z" (the coordinate) as the default. Alternatively, this can be the name of any other attribute, such as "Intensity", "gpstime", "ReturnNumber", or "HAG", if it exists. Note: The function does not fail if the specified attribute does not exist in the point cloud. For example, if "Intensity" is requested but not present, or "HAG" is specified but unavailable, the internal engine will return 0 for the missing attribute.
- record_attributes
The coordinates XYZ of points corresponding to the local maxima are recorded. It is also possible to record the attributes of theses points such as the intensity, return number, scan angle and so on.
- raster
LASRalgorithm. A stage that produces a raster.
Value
This stage produces a vector. The path provided to `ofile` is expected to be `.gpkg` or any other format supported by GDAL. Vector stages may produce geometries with Z coordinates. Thus, it is discouraged to store them in formats with no 3D support, such as shapefiles.
Examples
f <- system.file("extdata", "MixedConifer.las", package = "lasR")
read <- reader()
lmf <- local_maximum(5)
ans <- exec(read + lmf, on = f)
ans
#> Simple feature collection with 177 features and 0 fields
#> Geometry type: POINT
#> Dimension: XYZ
#> Bounding box: xmin: 481260 ymin: 3812921 xmax: 481349.8 ymax: 3813011
#> z_range: zmin: 2.42 zmax: 32.07
#> Projected CRS: NAD83 / UTM zone 12N
#> First 10 features:
#> geom
#> 1 POINT Z (481309.9 3812944 2...
#> 2 POINT Z (481294.7 3813011 16)
#> 3 POINT Z (481307.2 3813000 2...
#> 4 POINT Z (481281.9 3813003 2...
#> 5 POINT Z (481278.4 3813002 2...
#> 6 POINT Z (481265.3 3812996 1...
#> 7 POINT Z (481261.8 3812999 1...
#> 8 POINT Z (481302.9 3812929 2...
#> 9 POINT Z (481260.7 3812939 2...
#> 10 POINT Z (481262.9 3812935 1...
chm <- rasterize(1, "max")
lmf <- local_maximum_raster(chm, 5)
ans <- exec(read + chm + lmf, on = f)
# terra::plot(ans$rasterize)
# plot(ans$local_maximum, add = T, pch = 19)