I have LAS files with code 0 - never classified. I have no other classes other than this.
How do I assign class codes for my LAS file?
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It only takes a minute to sign up.Sign up to join this community
If the class codes field is not populated there is no way to obtain them. During pre-processing the vendor did not classify the points so, you are functionally dealing with a raw point cloud.
Unfortunately, this means that you need to start researching methods for classifying the point cloud yourself. Since you did not provide any context I cannot aim you towards specific resources for classification algorithms. The first step will invariably to classify ground returns then specialized algorithms can be applied to classify certain feature types (eg., buildings). A good software to start with is LASTools, which provides data management and limited classification tools. There is also a free software FUSION that provides some classification utilities. I would not that the ArcGIS LAS utilities for point cloud classification are lacking and one should really look at other software.
You could try and pull up a land use land cover database of your area where that code 0 is located in. It should be the similar one like this http://landcover.usgs.gov/landcoverdata.php but see if you have one the most recent current land use land cover of your area.