Query By Elevation versus Query by Depth
The basic ucvm_query gives user the option of query by depth (this is the default: -c gd) and query by elevation (-c ge).
These queries differ slightly:
Query by depth, the user specifies a numeric value (in meters) at or below the surface. A depth of 0 is at the surface, a depth of 100 is interpreted at 100m below the surface. So depths are nearly always positive numbers.
Query by elevation, the user specifies a numerical value (in meters) of elevation above or below sea level. An elevation of 0 is sea level. an elevation of 250 is an elevation of 250 meters above sea level. An elevation of -100 is 100 meters below sea level.
Please note that the user can query for elevations above the surface of the earth, which is "in the air".
To support query by elevation, UCVM contains a digital elevation model for California. The elevation of a given point is returned in column 4 of the return parameters. User can query a model, using any elevation or depth, and UCVM return the elevation of that point in column 4. The user use this information to determine whether the elevation is at the point, and then can query at that elevation to get material properties at the surface for that point.