Friday, February 19, 2010

Performance of GeoMedia Grid's Import LAS File to Feature Class command

I have tried GeoMedia Grid 6.1.1's Import LAS File to Feature Class command and I found it rather painful to use especially when processing hundreds of gigabytes worth of LAS files. Converting binary LiDAR points in LAS format files to read/write database feature class records is an expensive and time consuming process. You might be better off  filtering the LAS files to just what you need before using the Import LAS File to Feature Class command. For example, if I want to generate a bare earth DEM, I might only require LiDAR ground points; there is no point keeping the vegetation points or the building points.

I found the free command line programs LAStools on the Internet. It is quite useful to manipulate LAS files and it comes with the las2las executable. I use it to remove the LiDAR points that I do not want and retain the points that I want.

To see how to use this las2las executable, type in the following in a Windows Command Prompt as shown below:
C:\> las2las -h

To remove all points except the LiDAR ground points from a LAS file, you can type in the following in the Windows Command Prompt as shown below.

C:\> las2las -i input.las -o output.las -keep_class 2

where the value 2 is the standar LiDAR classification for ground points

Once I have filtered out the unwanted points, I then run GeoMedia Grid's Import LAS File to Feature Class command, which will run a little faster - because there would be less points to convert than before.

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