This page will give you enough info to covert .btg!
http://wiki.flightgear.org/index.php/BTG_File_Format


在2009-04-27,"Ranjana K" <ranjana.karunesh@gmail.com> 写道:
In need of Matlab source code or steps to convert .btg file which is obtained at the end of fgfs-construct to .hgt file.....Please reply as soon as possible....Thank you



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