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Reputation: 1039

Interpreting SRTM N34W119.hgt file

I am trying to interpret the data at the USGS site http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/North_America/

With my current understanding, the file N34W119.hgt represents one degree latitude (34 to 35) and one degree longitude(-119 to -118), this is Los Angeles (North America). So the first 2 bytes of this file represents altitude at (34' 0' 0") latitude and (-119' 0' 0") longitude. The value in file is (0x01ce) or 462 meters. But that doesn't match the value at the earthtools webservice http://www.earthtools.org/height/34/-119 or at daftlogic website http://www.daftlogic.com/sandbox-google-maps-find-altitude.htm which gives the altitude there as -9999 meters and ~ -18.287 meters respectively.

This surely tells me I am not interpreting things correctly. Can anyone throw some light on this problem?

Upvotes: 0

Views: 527

Answers (1)

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Reputation: 1039

Answering my own question.

The file N34W119.hgt represents one degree latitude by one degree longitude of earths surface. The point (34, -119) here represents the bottom left (South-West) point on this one degree by one degree space.

The file stores data starting from left to right and top to bottom. So here the first two bytes in the file represent the height in meters of point (35, -119) and the last two bytes in this file represent (34, -118)

Upvotes: 1

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