R: Add attributes into a LAS object

add_attribute {lidR} | R Documentation

## Add attributes into a LAS object

### Description

A LAS object represents a las file in R. According to the LAS specifications a las file contains a core of defined attributes, such as XYZ coordinates, intensity, return number, and so on, for each point. It is possible to add supplementary attributes.

### Usage

    add_attribute(las, x, name)

    add_lasattribute(las, x, name, desc)

    add_lasattribute_manual(
      las,
      x,
      name,
      desc,
      type,
      offset = NULL,
      scale = NULL,
      NA_value = NULL
    )

    add_lasrgb(las, R, G, B)

    remove_lasattribute(las, name)

### Arguments

`las` | An object of class LAS
`x` | a vector that needs to be added in the LAS object. For `add_lasattribute*` it can be missing (see details).
`name` | character. The name of the extra bytes attribute to add in the file.
`desc` | character. A short description of the extra bytes attribute to add in the file (32 characters).
`type` | character. The data type of the extra bytes attribute. Can be `"uchar", "char", "ushort", "short", "uint", "int", "uint64", "int64", "float", "double"`.
`scale, offset` | numeric. The scale and offset of the data. NULL if not relevant.
`NA_value` | numeric or integer. NA is not a valid value in a las file. At time of writing it will be replaced by this value that will be considered as NA. NULL if not relevant.
`R, G, B` | integer. RGB values

### Details

Users cannot assign names that are the same as the names of the core attributes. These functions are dedicated to adding data that are not part of the LAS specification. For example, `add_lasattribute(las, x, "R")` will fail because `R` is a name reserved for the red channel of a .las file that contains RGB attributes. Use `add_lasrgb` instead.

`add_attribute`

  Simply adds a new column in the data but does not update the header. Thus the LAS object is not strictly valid. These data will be temporarily usable at the R level but will not be written in a las file with writeLAS.

`add_lasattribute`

  Does the same as `add_attribute` but automatically updates the header of the LAS object. Thus, the LAS object is valid and the new data is considered as "extra bytes". This new data will be written in a las file with writeLAS.

`add_lasattribute_manual`

  Allows the user to manually write all the extra bytes metadata. This function is reserved for experienced users with a good knowledge of the LAS specifications. The function does not perform tests to check the validity of the information. When using `add_lasattribute` and `add_lasattribute_manual`, `x` can only be of type numeric, (`integer` or `double`). It cannot be of type `character` or `logical` as these are not supported by the LAS specifications. The types that are supported in lidR are types 0 to 10 (Table 24 on page 25 of the specification). Types greater than 10 are not supported.

`add_lasrgb`

  Adds 3 columns named RGB and updates the point format of the LAS object for a format that supports RGB attributes. If the RGB values are ranging from 0 to 255 they are automatically scaled on 16 bits.

### Value

An object of class LAS

### Examples

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

    print(las)
    print(las@header)

    x <- 1:30

    las <- add_attribute(las, x, "mydata")
    print(las)        # The las object has a new attribute called "mydata"
    print(las@header) # But the header has not been updated. This new data will not be written

    las <- add_lasattribute(las, x, "mydata2", "A new data")
    print(las)        # The las object has a new attribute called "mydata2"
    print(las@header) # The header has been updated. This new data will be written

    # Optionally if the data is already in the LAS object you can update the header skipping the
    # parameter x
    las <- add_lasattribute(las, name = "mydata", desc = "Amplitude")
    print(las@header)

    # Remove an extra bytes attribute
    las <- remove_lasattribute(las, "mydata2")
    print(las)
    print(las@header)

    las <- remove_lasattribute(las, "mydata")
    print(las)
    print(las@header)

[Package lidR version 3.2.2 Index]