LASF - ASPRS LIDAR Data Exchange Format Standard

Long name	ASPRS LIDAR Data Exchange Format ASPRS LIDAR Data Exchange Format Compressed Using LASzip
Short name	LASF LAZ
File extension(s)	.las, .laz

GDB supports the American Society for Photogrammetry and Remote Sensing (ASPRS) Light Detection And Ranging (LIDAR) LAS file format, versions 1.0, 1.1, and 1.2. GDB supports both read and write operations for LASF. You can view the specifications, known as the LASer (LAS) File Format Exchange Activities, on the ASPRS website at asprs.org.

This standard format is a binary file. It contains binary data consisting of a header, records of varying lengths, and LIDAR point-data records.

The header block consists of generic data, such as the number of points and coordinate bounds. The variable-length records include projection information and user-application data. Each point data contains x, y, and z coordinates and associated attributes. The point data can be delivered with up to five returns according to the limit defined by the format.

LAZ format

LASF has a compressed or zipped form known as LAZ. It is supported for read and write. Versions ranging from 1.0 through 1.4 are supported.

GDB "return" layers

GDB reads each LIDAR return number as a separate GDB vector layer.

GDB decodes the LASF file based on the return number. Each group of points with the same return number is added to a GDB vector layer. By doing so, up to five GDB vector layers are created. Because of the extremely large number of points, the GDB vector layers, (the "return" layers) are usually used for point processing and not viewed directly.

The last layer listed is the All Returns layer, which contains the points from all the other layers.

GDB vector-layer attributes

Each GDB vector layer has the following attributes, as defined in the LAS specification:

Intensity
Return Number
Number of Returns
Scan Direction Flag
Edge of Flight Line
Classification
Scan Angle Rank
File Marker
User Bit Field
GPS Time (point formats 1 and 3 only)
Red, Green, and Blue values for colorization (point formats 2 and 3)

Exporting to LASF

When exporting GDB vector layers to the LASF file format, the input vector layers must have the preceding attributes and associated values. If the vector layers do not have these attributes, GDB creates them in the output LASF file with default values.

Georeferencing

GDB reads any projection information in the LASF file. When exporting the projection information, GDB stores the projection definition by using GeoTIFF tags.

Storage of point locations

The LASF format stores point locations of x, y, and z in 4-byte integers. GDB stores point locations by using double-precision floating-point numbers.

When exporting to the LASF file format, GDB uses a scale factor and offset to convert the GDB double-precision locations to LASF-integer locations.

Note: Some loss of precision may occur during conversion.

GDB calculates an appropriate scale factor and offset for the layer from the first point in the layer. If necessary, you can manually enter values for the layer—for example, when you have values of superior quality— in the metadata for the "X Scale", "Y Scale", "Z Scale", "X Offset", "Y Offset" and "Z Offset" tags.