cdfaltmap −− accepts data from the NCAR 30 second resolution terrain elevation map for the United States and converts specified regions to Candis format
cdfaltmap lat_low lat_high lon_low lon_high
The National Center for Atmospheric Research (NCAR) distributes a tape that contains terrain elevation information at 30 second intervals over the continental United States. Cdfaltmap expects this data file on the standard input after it has been transferred to disk using the utility rtape. A Candis file appears on the standard output containing elevation data within the latitude and longitude limits specified on the command line. (Longitudes over the United States are considered to be negative.)
The arrangement of data on the original tape is by constant latitude stripes. The output is in the form of variable slices, each containing all data for a given latitude of the desired map as well as the value of the latitude. Application of cdfcat as shown below creates a single variable slice containing the two−dimensional field "alt" as a function of "lat" and "lon". Unfortunately, the order of lat and lon creates maps with north to the right. Cdforder can be used to transpose the file so that maps may be plotted in the conventional fashion.
Elevation is given in terms of kilometers above sea level.
kestrel%cdfaltmap 31 37 −110 −103 < raw.map.file > temp_file
This would extract the data from raw.map.file that contains the elevations of points within New Mexico. Cdfcat and cdforder should then be used to place the data into standard arrangement as follows:
kestrel%cdfcat lat 31 37 1000 < temp_file | cdforder lon lat > nm.map
The last argument of cdfcat is calculated on the basis that there are (37 − 31)*60*2 + 1 = 721 variable slices in temp_file, one for each latitude line. The value of 1000 is a round number that exceeds 721. A safe approach is to allocate 125 for each degree of latitude desired in the final map file.