I've just added basic ability to display LAS files directly within the main map window of the open source GIS Whitebox Geospatial Analysis Tools. LAS points can be rendered based on their elevation or intensity values. I still have a bit to do before this work is complete. Specifically, I will need to add a dialog for manipulating LAS display properties and incorporating this into the Whitebox legend. Nonetheless, I'll incorporate this functionality in the next public release of the software (v. 3.2.1).
Okay, the weekend has come and gone so I thought I'd give you an update on the progress of adding the ability to display LAS files in Whitebox GAT. As you can see in the image below, you can now add LAS files to a Whitebox Map Area in the same way that you would add a typical raster or vector file. It can be overlayed on top of other types of geospatial data and you can now manipulate a LAS file's display properties including changing its colour palette, display minimum and maximum value, rendering colours by elevation values or intensity, altering the transparency, and modifying the point size. This last characteristic is important because it determines the level of detail with which the LAS file is displayed. In order to increase the display speed and the ability to navigate the image (zoom in and out, pan, etc.) the program figures out how many LAS points there are within the current window's extent and the space available to display them in. That, combined with the size of each point as displayed (the marker size) determines whether it displays every point, every second point, third, and so on. When you zoom into the image, eventually you will see every point available and the full level of detail (see detailed image below). This all occurs on the fly. I find it works well.
I still have some work to do in incorporating LAS data into the Whitebox map files saved to disc and incorporating them into the map legend. I think, however, that this is a functioning method for displaying LAS files natively within an open-source GIS. I'll post the code to the Whitebox repository today and will make it available in a compiled format in the next public release, which should be soon.
I've just released the latest version of the software, which includes the new functionality described in this post.