function HeadingToDegree(Heading: integer): Extended;
begin
Result:=(heading - 32768) / (32768/pi)*(180 / pi);
if Result<=0 then Result:=Result+360;
end;

Ну или если упростить:
function HeadingToDegree(Heading: integer): Extended;
begin
Result:=((heading - 32768) / 32768)*180;
if Result<=0 then Result:=Result+360;
end;