Altitude in Km above sea level for a given pair of coordinates (lat,long)

Calculates the altitude of any site in the world, in Km above sea level.

%function alt_km=ITU_P1511(lat,long)
%computes altitude of a site at given lat,long coordinates
%by means of bicubic interpolation using itu topo 0.5 degrees resolution
%matrix.
%refer to ITU-R Recommendation P 1511.
%
%INPUTS
%lat: latitude + = North, -=south
%long: longitude, positive degrees East.
%
%Required data: TOPO_0d5.txt, available from the ITU-R SG3 software site
%http://www.itu.int/ITU-R/study-groups/software/rsg3-p1511-topography.zip
%http://www.itu.int/ITU-R/index.asp?category=documents&link=rsg3&lang=en
%example of usage:
%alt_km=ITU_P1511(52,0); %somewhere in the UK
%Luis Emiliani. Rel. 16/01/2009