On Sun, Jun 2, 2013 at 10:50 AM, Claudius <gpsbabel.list@wolki.de> wrote:
As most research was a dead-end, i decided to tweak the values "until it
fits". I am happily compiling my own gpsbabel now. Only the libqt4-dev
dependency was missing from the how-to guide, but that was fixed quickly.

Right now, i am taking the altitude and convert it linearly with this line:

> double converted_alt = -alt / 3.28084 + 150;

That's FEET_TO_METERS for us.  It's very odd that a device would be reporting feet, but I suppose it can happen.
What the 150-constant is, i have no idea. It's just the offset to bring
my first track into the -more or less- right altitude.
I wonder if the 150 is about what http://www.gpsbabel.org/htmldoc-development/filter_height.html would create.