SRTM3 data is supposed to overlap, but it doesn't quite. and the closest it comes to overlapping is the first row of the lower latitude file with the last row of the higher-latitude file, at the same longitude. ergo:

>>> s=get_row(read(get_hgt_file('36', '-117')[0]), 1200)
DEBUG:root:rowdata: '\x04\xd3\x04\xcd\x04\xc5\x04\xbe\x04\xba\x04\xb7
\x04\xb0\x04\xa8\x04\xb1\x04\xc2\x04\xc2\x04\xcf\x04\xf2\x05\x1b\x05:\x050' ...
>>> s=get_row(read(get_hgt_file('35', '-117')[0]), 0)
DEBUG:root:rowdata: '\x04\xd3\x04\xcc\x04\xc4\x04\xbe\x04\xbb\x04\xb7
\x04\xb0\x04\xaa\x04\xb8\x04\xc6\x04\xc5\x04\xdc\x05\x02\x05)\x05=\x05/' ...
>>> s=get_row(read(get_hgt_file('35', '-117')[0]), 1200)
DEBUG:root:rowdata: '\x03I\x03H\x03F\x03E\x03D\x03D\x03D\x03D\x03C
\x03C\x03C\x03C\x03C\x03C\x03C\x03C' ...
>>> s=get_row(read(get_hgt_file('34', '-117')[0]), 0)
DEBUG:root:rowdata: '\x03H\x03G\x03E\x03E\x03D\x03C\x03C\x03C\x03C
\x03C\x03C\x03C\x03B\x03B\x03B\x03B' ...
>>> s=get_row(read(get_hgt_file('34', '-117')[0]), 1200)
DEBUG:root:rowdata: '\x04\t\x04(\x049\x04`\x04\x83\x04\x85\x04i\x04L
\x04;\x04E\x04D\x04@\x04(\x04\x17\x04\x15\x04\r' ...
>>> s=get_row(read(get_hgt_file('33', '-117')[0]), 0)
DEBUG:root:rowdata: '\x04\t\x04*\x044\x04X\x04v\x04\x93\x04u\x04Y\x04E
\x04R\x04R\x04F\x04+\x04\x1f\x04\x1d\x04\x12' ...

this implies, to me, that the last row in sequence is actually the first row in latitude, e.g. the final 2402 bytes of data in N36W117.hgt are the heights starting from 36 degrees north, 117 degrees west. damned if I can find that spelled out in the (PDF) documentation.

now I've got to figure out the column overlapping.

Back to blog or home page

last updated 2016-03-22 15:19:16. served from tektonic.jcomeau.com