Heading Equation

[Michael A]

Hi guys,

Im still having a problem with the heading equation for offset 0580.

Code snippet below...

var
 heading : DWord;
begin
 FSUIPC_Read($0580, 4, @heading, dwResult);
 Hdg.Caption := FloattoStr(heading*360/(65536*65536))+'º';
end;

Its the only problem i seem to be having and it looks simple in the programmers guide.

Any help?

Cheers

Mick.

[Michael A]

Hi again,

Never mind, I worked it out.

Hdg.Caption := CurrtoStr(heading*360.0/(65536.0*65536.0))+'º';

Then I just did the TRUE to MAG conversion and all is now fine.

Cheers,

Mick

[Pete Dowson]

FSUIPC_Read($0580, 4, @heading, dwResult);

Hdg.Caption := FloattoStr(heading*360/(65536*65536))+'º';

[/code]

Its the only problem i seem to be having and it looks simple in the programmers guide.

You really need to try using FSInterrogate. It can help clarify most of these sorts of misunderstanding. That's why it is provided.

You are correctly reading the 32-bit (4-byte) heading into an unsigned integer variable (at least, that's how I assume Dword is defined?). But this is fixed point, not floating point. What does your "FloattoStr" do when fed with a fixed point number?

Try converting the heading to a double floating point value first. In C this can be done automatically by:

(heading*360.0)/(65536.0*65536.0)

The ".0" bits make all the difference, in C at least. I assume you are using VB, so I'm not really sure what will be happening in the code you are showing.

Also, I always like to be explicit with parentheses. In C I know the multiplication will be done first anyway, but will it be so in VB? If not you are actually multiplying by zero: 360/(65536*65536) is zero in fixed point. It is possible that the compiler is optimising the code and converting the 360/(65536*65536) part even before you get to run the code.

Regards,

Pete