When I started writing PFM and PFMABE I was working for the U.S. Naval Oceanographic Office. Our primary goal was to collect and process bathymetric and hydrographic data. We didn’t even look at topographic data… until we started playing around with LiDAR. I was already 20 years in to writing software to process sonar data by the time we got a reasonable bathymetric LiDAR. Why is this important? Because PFMABE is designed for hydrographers. Those strange people who think that the Marianas Trench is plus 11,000 meters deep and Mount Everest is minus 9,000 meters high. So, everything in PFMABE is treated as a depth. Does this mean we display the surfaces and points upside down? Of course not. You just have to get used to mentally erasing the negative sign from the beginning of values that are physically above your zero value. It becomes pretty easy after a while. Most of the programs that deal with LiDAR outside of the surface viewers and the editor will display values in elevations because that is how they are stored in the data files (CHARTS, CZMIL, LAS). Generic Sensor Format (GSF) data will always be displayed as depths.