R: Decimate a LAS object

decimate_points {lidR} | R Documentation

## Decimate a LAS object

### Description

Reduce the number of points using several possible algorithms.

### Usage

    decimate_points(las, algorithm)

### Arguments

`las` | An object of class LAS or LAScatalog.
`algorithm` | function. An algorithm of point decimation. `lidR` have: random, homogenize, highest, lowest and random_per_voxel.

### Value

If the input is a `LAS` object, returns a `LAS` object. If the input is a `LAScatalog`, returns a `LAScatalog`.

### Working with a `LAScatalog`

This section appears in each function that supports a LAScatalog as input.

In `lidR` when the input of a function is a LAScatalog the function uses the LAScatalog processing engine. The user can modify the engine options using the available options. A careful reading of the engine documentation is recommended before processing `LAScatalogs`. Each `lidR` function should come with a section that documents the supported engine options.

The `LAScatalog` engine supports `.lax` files that significantly improve the computation speed of spatial queries using a spatial index. Users should really take advantage a `.lax` files, but this is not mandatory.

### Supported processing options

Supported processing options for a `LAScatalog` (in bold). For more details see the LAScatalog engine documentation:

- chunk size: How much data is loaded at once.

- chunk buffer: This function guarantee a strict wall-to-wall continuous output. The `buffer` option is not considered.

- chunk alignment: Align the processed chunks.

- progress: Displays a progression estimation.

- output files*: Mandatory because the output is likely to be too big to be returned in R and needs to be written in las/laz files. Supported templates are `{XLEFT}`, `{XRIGHT}`, `{YBOTTOM}`, `{YTOP}`, `{XCENTER}`, `{YCENTER}` `{ID}` and, if chunk size is equal to 0 (processing by file), `{ORIGINALFILENAME}`.

- select: The function will write files equivalent to the original ones. Thus `select = "*"` and cannot be changed.

- filter: Read only points of interest.

### Examples

    LASfile <- system.file("extdata", "Megaplot.laz", package="lidR")
    las = readLAS(LASfile, select = "xyz")

    # Select points randomly to reach an overall density of 1
    thinned1 = decimate_points(las, random(1))
    #plot(grid_density(las))
    #plot(grid_density(thinned1))

    # Select points randomly to reach an homogeneous density of 1
    thinned2 = decimate_points(las, homogenize(1,5))
    #plot(grid_density(thinned2))

    # Select the highest point within each pixel of an overlayed grid
    thinned3 = decimate_points(las, highest(5))
    #plot(thinned3)

[Package lidR version 3.2.2 Index]