Elevation a specific lat/long with DTED

In my code I import DTED data for a given area. I break that area up into a grid and would like to classify each box as either land or ocean. The DTED import gives me Z (elevation in meters) and refvec (reference vector). Is there a built in Matlab function whose imports are Z, refvec and a specific lat/long that returns the elevation at that point? Or do I need to need to do some math myself to get the elevation at a the center of each box? Elevation at a given lat/long seems like a common need so I thought I would ask before attempting to reinvent the wheel.