how to read NASA .hgt binary files

Question

I'm sure this is really simple if you know anything about binary files, but I'm a newbie on that score.

How would I extract the data from NASA .hgt files? Here is a description from www2.jpl.nasa.gov/srtm/faq.html:

The SRTM data files have names like "N34W119.hgt". What do the letters and numbers refer to, and what is ".hgt" format?

Each data file covers a one-degree-of-latitude by one-degree-of-longitude block of Earth's surface. The first seven characters indicate the southwest corner of the block, with N, S, E, and W referring to north, south, east, and west. Thus, the "N34W119.hgt" file covers latitudes 34 to 35 North and longitudes 118-119 West (this file includes downtown Los Angeles, California). The filename extension ".hgt" simply stands for the word "height", meaning elevation. It is NOT a format type. These files are in "raw" format (no headers and not compressed), 16-bit signed integers, elevation measured in meters above sea level, in a "geographic" (latitude and longitude array) projection, with data voids indicated by -32768. International 3-arc-second files have 1201 columns and 1201 rows of data, with a total filesize of 2,884,802 bytes ( = 1201 x 1201 x 2). United States 1-arc-second files have 3601 columns and 3601 rows of data, with a total filesize of 25,934,402 bytes ( = 3601 x 3601 x 2). For more information read the text file "SRTM_Topo.txt" at http://edcftp.cr.usgs.gov/pub/data/srtm/Readme.html

Thanks for any help! I am going to use this data in a python script, so if you could not use any language-specific tricks for any other languages, that would be awesome.

Answer 1

A tested numpy example:

import os
import math
import numpy

fn = 'DMV/N51E000.hgt'

siz = os.path.getsize(fn)
dim = int(math.sqrt(siz/2))

assert dim*dim*2 == siz, 'Invalid file size'

data = numpy.fromfile(fn, numpy.dtype('>i2'), dim*dim).reshape((dim, dim))