Less Basic Things

Extra Dimensions

The LAS Specification version 1.4 defines a standard way to add extra dimensions to a LAS file.

In pylas you can add extra dimensions using the pylas.lasdatas.base.LasBase.add_extra_dim() function

The Allowed base types for an extra dimensions are:

pylas name size (bits) type
u1 or uint8 8 unsigned
i1 or int8 8 signed
u2 or uint16 16 unsigned
i2 or int16 16 signed
u4 or uint32 32 unsigned
i4 or int32 32 signed
u8 or uint64 64 unsigned
i8 or int64 64 signed
f4 or float 32 floating
f8 or double 64 floating

You can prepend the number ‘2’ or ‘3’ to one of the above base type to define an extra dimension that is array of 2 or 3 elements per points. Example: 3u2 -> each points will have an extra dimension that is an array of 3 * 16 bits

Here we are adding a new dimension called “codification” where each value is stored on a 64 bit unsigned integer and an array field of 3 doubles for each points.

import pylas
las = pylas.read("somefile.las")

las.add_extra_dim(name="codification", type="uint64", description="More classes available")

las.add_extra_dim(name="mysterious", type="3f8")

Note

Although the specification of the ExtraBytesVlr appeared in the 1.4 LAS Spec, pylas allows to add new dimensions to file with version < 1.4

Custom VLRs

Provided you have a valid user_id and record_id (meaning that they are not taken by a VLR described in the LAS specification) You can add you own VLRs to a file

Fast & Easy way

The fastest and easiest way to add your custom VLR to a file is to create a pylas.vlrs.rawvlr.VLR, set its record_data (which must be bytes) and add it to the VLR list.

>>> import pylas
>>> vlr = pylas.vlrs.VLR(user_id='A UserId', record_id=1, description='Example VLR')
>>> vlr
<VLR(user_id: 'A UserId', record_id: '1', data len: 0)>
>>> vlr.record_data = b'somebytes'
>>> vlr
<VLR(user_id: 'A UserId', record_id: '1', data len: 9)>
>>> las = pylas.create()
>>> las.vlrs
[]
>>> las.vlrs.append(vlr)
>>> las.vlrs
[<VLR(user_id: 'A UserId', record_id: '1', data len: 9)>]

Complete & Harder way

While the way shown above is quick & easy it might not be perfect for complex VLRs. Also when reading a file that has custom VLR, pylas won’t be able to automatically parse its data into a better structure, so you will have to find the VLR in the vlrs list and parse it yourself one pylas is done.

One way to automate this task is to create your own Custom VLR Class that extends pylas.vlrs.BaseKnownVLR by implementing the missing methods pylas will be able to automatically parse the VLR when reading the file & write it when saving the file.

>>> class CustomVLR(pylas.vlrs.BaseKnownVLR):
...     def __init__(self):
...         super().__init__()
...         self.numbers = []
...
...     @staticmethod
...     def official_user_id():
...         return "CustomId"
...
...     @staticmethod
...     def official_record_ids():
...         return 1,
...
...     def record_data_bytes(self):
...         return bytes(self.numbers)
...
...     def parse_record_data(self, record_data):
...         self.numbers = [b for b in record_data]
...
...     def __repr__(self):
...         return "<MyCustomVLR>"
>>> import numpy as np
>>> cvlr = CustomVLR()
>>> cvlr.numbers
[]
>>> cvlr.numbers = [1,2, 3]
>>> las = pylas.create()
>>> las.vlrs.append(cvlr)
>>> las.vlrs
[<MyCustomVLR>]
>>> las.x = np.array([1.0, 2.0])
>>> las = pylas.lib.write_then_read_again(las)
>>> las.vlrs
[<MyCustomVLR>]
>>> las.vlrs[0].numbers
[1, 2, 3]