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*********************************************
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*********************************************
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This basic tutorial explains how to use libLAS to read and write
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LIDAR data encoded in LAS file format from Python.
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=============================================
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=============================================
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1. Reading LAS data in Python is a simple as opening the file with the
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file.File class and using the iterator to chug through the points.
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.. code-block:: python
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>>> from liblas import file
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>>> f = file.File('file.las',mode='r')
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... print 'X,Y,Z: ', p.x, p.y, p.z
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2. You can also read specific points from a file:
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.. code-block:: python
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>>> from liblas import file
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>>> f = file.File('file.las', mode='r')
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<liblas.point.Point object at 0x7377f0>
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File versions and formats
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------------------------------------------------------------------------------
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The LAS format, as of this writing, provides three different file format
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versions (1.0, 1.1, and 1.2) and four different point format verions (0, 1, 2, 3).
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It is important that you be mindful of the minor_version and the dataformat_id
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when working with files. If the dataformat_id is not correct for the type of
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data you want to store (color, time, or color + time), none of that data will
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be read or written, even though placeholders will exist on the liblas.point
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.. csv-table:: Point format versions and their properties
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:header: "dataformat_id", "Time", "Color"
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You control whether or not color, time, or color + time is stored in the
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file by setting the dataformat_id in the header that you use to create
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the file.File. This has to be done when you instantiate the file, it
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cannot be changed after the fact. Attempting to do so may result in
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.. csv-table:: Base properties of all points regardless of dataformat_id
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=============================================
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=============================================
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Headers, points, VLRs, colors, and GUIDs are *copies*, not references in
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the libLAS Python bindings. After opening a LAS file, you can fetch
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the header with the following property:
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.. code-block:: python
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<liblas.header.Header object at 0x737790>
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------------------------------------------------------------------------------
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There are many properties of the header that you can get and set:
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.. code-block:: python
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>>> h.major_version, h.minor_version
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[289020.90000000002, 4320942.6100000003, 166.78]
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[290106.02000000002, 4323641.5700000003, 215.48000000000002]
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>>> h.point_records_count
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>>> from liblas import guid
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'00000000-0000-0000-0000-000000000000'
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00000000-0000-0000-0000-000000000000
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5cb59173-124b-476b-9729-bafa87cfb27c
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5cb59173-124b-476b-9729-bafa87cfb27c
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'5cb59173-124b-476b-9729-bafa87cfb27c'
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# only works if you have libgeotiff and/or GDAL linked in
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+proj=tmerc +lat_0=0.000000000 +lon_0=-93.000000000 +k=0.999600 \
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+x_0=500000.000 +y_0=0.000 +ellps=WGS84 +units=m
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=============================================
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=============================================
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The liblas.point module contains a Point class that you can use to manipulate
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LAS point data. It is fairly basic and contains a number of properties you
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.. code-block:: python
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(289814.15000000002, 4320978.6100000003, 170.75999999999999)
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>>> p.number_of_returns
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>>> p.flightline_edge
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datetime.datetime(1970, 1, 6, 12, 44, 10, 1)
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=============================================
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=============================================
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Variable Length Records (VLR) are frequently used by applications to store
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anything they wish in the file as a "blob" written into the header of the
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file. libLAS supports writing and creating your own VLRs in addition to
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taking on the work of interpreting and using VLR records related to
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spatial reference systems if GDAL and proj.4 are linked into the library.
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The following code demonstrates how to write your own VLR by opening an
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XML file and inserting it into a new file.
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.. code-block:: python
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from liblas import file as lasfile
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from liblas import vlr
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from liblas import header as lasheader
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f = lasfile.File('test/data/srs_utm17.las',None,'rb')
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text = open('schemas/las.xml','rb').read()
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data = ctypes.create_string_buffer(text)
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f2 = lasfile.File('junk.las',header=h,mode='w')
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=============================================
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=============================================
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To write a new LAS file, you are first required to have a header. The header
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will have a number of default values, but it is important to set the
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dataformat_id and version_minor if you wish to have 1.1 files or records that
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also include time values.
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.. code-block:: python
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>>> from liblas import header
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>>> h = header.Header()
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### Support storing time values
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>>> h.dataformat_id = 1
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### Store a 1.1 version file
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>>> h.minor_version = 1
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Another important item to not is possible to have the same file open for
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read and write at the same time because LAS files are sequential. For example,
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the following will fail:
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.. code-block:: python
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>>> f = file.File('junk.las', mode="w", header=h)
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>>> f2 = file.File('junk.las')
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Traceback (most recent call last):
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LASException: ('File %s is already open. Close the file or delete the reference to it', 'junk.las')
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Writing to a LAS file is as simple as opening the file for write mode
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with the header you want to write and issuing the write() command with some
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liblas.point.Point instances:
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.. code-block:: python
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>>> f = file.File('junk.las',mode='w', header= h)
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>>> pt = liblas.point.Point()
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doc/tutorial/python.txt
