Compression

Exercise

This exercise uses PDAL to compress ASPRS LAS data into LASzip.

1. Issue the following command in your Conda Shell.

   $ pdal translate ./exercises/translation/interesting.las \
   ./exercises/translation/interesting.laz
   

   The translate command converts files based on their extensions.

   > pdal translate ./exercises/translation/interesting.las ^
   ./exercises/translation/interesting.laz
   

   Note

   LAS is a very fluffy binary format. Because of the way the data are stored, there is ample redundant information, and LASzip is an open source solution for compressing this information. Note that we are actually inflating the data here. Its laz from the workshop and we are converting it to las.

2. Verify that the laz data is compressed over the las:

   $ ls -alh  ./exercises/translation/interesting.la*
   ...
   

   > dir ./exercises/translation/interesting.la*
   ...
   

Output:

-rw-r--r--@ 1 ogi  staff    36K Aug  8  2019 ./exercises/translation/interesting.las
-rwxr-xr-x@ 1 ogi  staff    18K May  9 11:30 ./exercises/translation/interesting.laz

See also

LAS Reading and Writing with PDAL contains many pointers about settings for ASPRS LAS data and how to achieve specific data behaviors with PDAL.

Notes

1. Typical LASzip compression is 5:1 to 8:1, depending on the type of LiDAR. It is a compression format specifically for the ASPRS LAS model, however, and will not be as efficient for other types of point cloud data.

2. You can open and view LAZ data in web browsers using http://plas.io but we will be using QGIS as examples.