My maths and I have parted comapny again.... I'm trying to decide whether I need to initiate a turn to the left or to the right, depending on the current and target headings. I thought this worked, but it doesn't and after an hour or so of trying, I can no longer see the wood for the trees. Would someone be kind enough to cast an eye over it and tell me what's worong?Thank you.-Dai

int getDirection(int hdg, int target){	int direction=0;	hdg=hdg+180;	if(hdg>360)hdg-=360;	if(target<hdg)direction=2;	//turn right	else direction=1;		//turn left	return direction;}

int getDirection(int hdg, int target) {   int direction=0;   int diff;  diff = abs(hdg-target);  if (diff <= 180)  {    if (target >= hdg)      direction = 2;    else      direction = 1;  }  else  {    if (hdg >= target)      direction = 2;    else      direction = 1;  }  return direction; }

Try a general function to normalise angles , which can be useful elsewhere too.

int NormaliseAngle(int a){while (a >= 360)    a = a - 360;     while (a < 0)    a = a +360;return a;}  

Then you can write

 if (Normalise(target) > Normalise(hdg))    Direction = 2;else    Direction = 1;ORNormalise(target) > Normalise(hdg) ? Direction = 2 : Direction = 1;   

To turn right if target is greater than hdg.

Thank you both very much!!-Dai

Both whom?? I just see you and I in the thread. :(

Both whom?? I just see you and I in the thread. :(

You may have some folks "blocked from view" in your User Control Panel... :( Gerry provided a very good example as well, using a function call to normalize the angles before testing for direction.

Ah... 'mgh'... yes, blocked: intentionally. The new forum makes blocked posts almost unnoticeable. Also, his example doesn't actually do what's required:Based on his code, using the following values:target = 270hdg = 010Normalize(270) will return 270, thus not 'normalized' at allNormalize(010) will return 010, also not 'normalized' at all270 (target) is greater than 010 (hdg) and based on his code will have you turn right... yet shortest distance is to the left.

270 (target) is greater than 010 (hdg) and based on his code will have you turn right... yet shortest distance is to the left.

Oh, okay. I hadn't actually parsed it out, but it sure looks pretty!

Ah... 'mgh'... yes, blocked: intentionally. The new forum makes blocked posts almost unnoticeable. Also, his example doesn't actually do what's required:Based on his code, using the following values:target = 270hdg = 010Normalize(270) will return 270, thus not 'normalized' at allNormalize(010) will return 010, also not 'normalized' at all270 (target) is greater than 010 (hdg) and based on his code will have you turn right... yet shortest distance is to the left.

The angles are normalised in the usual way for integers to be in the range 0 to +359. Agreed the following code doesn't find the shortest distance. But then neither does your function. Try it with hdg = 2 and tgt = -359. That turns right not left Also it gives inconsistent answers - hdg = 1, tgt = 360 results in a left turn but hdg = 1, tgt = -360 results in a right turn yet -360 is the same direction as +360.

The angles are normalised in the usual way for integers to be in the range 0 to +359. Agreed the following code doesn't find the shortest distance. But then neither does your function. Try it with hdg = 2 and tgt = -359. That turns right not left Also it gives inconsistent answers - hdg = 1, tgt = 360 results in a left turn but hdg = 1, tgt = -360 results in a right turn yet -360 is the same direction as +360.

The original request was how to calculate the shortest turn distance based on current and desired heading. Your code won't do that, and there is no such thing as a -360 heading. I've looked at the compass repeatedly, just to be certain I didn't miss anything. An autopilot wouldn't have a 'target' of a negative value. A waypoint doesn't have a desired track that's a negative value. Like anything else on a computer, garbage in: garbage out. If you're passing negative values that aren't even negative in the real world... you're going to get incorrect results.

The original request was how to calculate the shortest turn distance based on current and desired heading. Your code won't do that, and there is no such thing as a -360 heading. I've looked at the compass repeatedly, just to be certain I didn't miss anything. An autopilot wouldn't have a 'target' of a negative value. A waypoint doesn't have a desired track that's a negative value. Like anything else on a computer, garbage in: garbage out. If you're passing negative values that aren't even negative in the real world... you're going to get incorrect results.

A computer will calculate a negative heading - regardless of the markings on a compass. Just as easily as it will calculate one greater that 360. That's why they need to be normalised before use. Your function fails unless the angles are normalised before use.

You are arguing to 'argue'... pretty much all you ever do and why I put you on my ignore list to begin with.Your code accomplishes one thing and only one thing... ensures that the values range between 0 and 359. It doesn't actually address the OP's request at all. Your code will never return the shortest turn direction if the target and heading values cross the 000/360 boundary. The shortest turn direction is exactly what the OP wanted to obtain, not a function to keep the heading and target within 0-359, which I'm certain a 2nd grader could explain how to accomplish (not meant as an insult... it's just really that simple).It is not unreasonable for my function to expect that both target and heading fall within the 0-359 range... and for you to imply that the expectation is incorrect is simply you wanting to argue because it's grossly important to you to always be 'right'... even if you have to actually change the discussion point to accomplish it. Something you do in almost every topic you enter into at AVSIM. Now... you're back on ignore and staying there. You've proven once again that your sole purpose for being at AVSIM is to be disruptive and argumentative.

I accepted that my code didn't find the shortest distance.Can you accept that this is wrong?

Normalize(270) will return 270, thus not 'normalized' at allNormalize(010) will return 010, also not 'normalized' at all

Sorry, I've just realised you won't see this.