How to create terrain file using IMG files?

Hi,

I want to create 3D terrain file from available data in TNRIS. There are some available file types: LIDAR cloud points (LAZ), Disc Image File (IMG) and corresponding XML Documents. 

I tried "Import terrain model from file" command in OenRoad. The area is divided into tiles, each tile includes smaller tiles. I imported couple of smaller tiles and the file broke. 

I really appreciate it if you can guide me what the problem is. Or if my method in importing and creating file is wrong, show me the right method. I can use OpenRoad or GeoPak.

I guess my general question, what is the procedure to download IMG or LAZ file and create TIN file. 

Thanks in advance. 

Regards,