Thread Subject: is my subject looking at the target?

I am trying to write a bit of code that will allow me to
determine when a subject is gazing at an object in space.
Here is what I have to work with:
1. Position of the subject (X and Y coordinates, we ignore Z)
2. The angle of the head
3. The position of the object (again X and Y)
What I need to do is first create a target around the object
position (a circle centered at the object position with some
user defined radius) and then determine if the subject is
gazing at the target (a simple yes or no).
This should be straightforward, but I am new to Matlab and
am having a hard time coming up with a solution. If anyone
can help, that would be great. Thanks!

"Dave Rowland" <rowland@uoneuro.uoregon.edu> wrote in message <fnjif9
$59p$1@fred.mathworks.com>...
> I am trying to write a bit of code that will allow me to
> determine when a subject is gazing at an object in space.
> Here is what I have to work with:
> 1. Position of the subject (X and Y coordinates, we ignore Z)
> 2. The angle of the head
> 3. The position of the object (again X and Y)
> What I need to do is first create a target around the object
> position (a circle centered at the object position with some
> user defined radius) and then determine if the subject is
> gazing at the target (a simple yes or no).
> This should be straightforward, but I am new to Matlab and
> am having a hard time coming up with a solution. If anyone
> can help, that would be great. Thanks!
--------
  Let (xs,ys) be coordinates of the subject's position [1.] and (xt,yt) be those
of the target [3.]. Let 'as' be the angle of the subject's head [2.]. Finally, let r
be the user-defined radius.

 d2 = (xt-xs)^2+(yt-ys)^2-r^2; % Square of dist. to tangent pt.
 if d2 >= 0
  ah = atan2(r,sqrt(d2)); % Half of target's projected arc
  at = atan2(yt-ys,xt-xs); % Angle from subject to target
  df = mod(at-as+pi,2*pi)-pi; % Difference in angles
  if abs(df) <= ah
   fprintf('Subject is gazing at object.\n')
  else
   fprintf('Subject is not gazing at object.\n')
  end
 else
  fprintf('Subject is inside circle.\n')
 end

Roger Stafford

"Roger Stafford" <ellieandrogerxyzzy@mindspring.com.invalid>
wrote in message <fnkk5e$o5g$1@fred.mathworks.com>...
> "Dave Rowland" <rowland@uoneuro.uoregon.edu> wrote in
message <fnjif9
> $59p$1@fred.mathworks.com>...
> > I am trying to write a bit of code that will allow me to
> > determine when a subject is gazing at an object in space.
> > Here is what I have to work with:
> > 1. Position of the subject (X and Y coordinates, we
ignore Z)
> > 2. The angle of the head
> > 3. The position of the object (again X and Y)
> > What I need to do is first create a target around the object
> > position (a circle centered at the object position with some
> > user defined radius) and then determine if the subject is
> > gazing at the target (a simple yes or no).
> > This should be straightforward, but I am new to Matlab and
> > am having a hard time coming up with a solution. If anyone
> > can help, that would be great. Thanks!
> --------
> Let (xs,ys) be coordinates of the subject's position
[1.] and (xt,yt) be those
> of the target [3.]. Let 'as' be the angle of the
subject's head [2.]. Finally, let r
> be the user-defined radius.
>
> d2 = (xt-xs)^2+(yt-ys)^2-r^2; % Square of dist. to
tangent pt.
> if d2 >= 0
> ah = atan2(r,sqrt(d2)); % Half of target's projected arc
> at = atan2(yt-ys,xt-xs); % Angle from subject to target
> df = mod(at-as+pi,2*pi)-pi; % Difference in angles
> if abs(df) <= ah
> fprintf('Subject is gazing at object.\n')
> else
> fprintf('Subject is not gazing at object.\n')
> end
> else
> fprintf('Subject is inside circle.\n')
> end
>
> Roger Stafford
>
thanks! it's working well.