just to clear up a misconception, the SRTM is just unusable in it's normal form, you need a lot of time to clean it up and cross it with other sources. This guy does a lot of curation: http://www.viewfinderpanoramas.org/dem3.html

(and I also suck google's elevation data for a test because that's the simplest way to do it: http://nraynaud.github.io/webgcode/test_threejs.html )