error454/Leap Explanation.md

## Leap Explanation.md

      
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              Leap Explanation.md
            
          
    leapFrame.js defines a function that helps you read and act on a single frame of leap data.

The leap device passes 'frames' of data as it sees objects in the world.  A single frame of data has information on how many objects are seen, what direction they're pointing, where they're located in 3D space etc.  Take time and look at leapFrame.js and the functions it provides:

palm position
palm direction
palm normal vector
finger position
finger angle
delta finger position

If you need some help figuring out what some of these vectors look like, take a look at the leap documentation, they have nice pictures showing all the axis etc.
joint.js defines a function that helps create and move joints.  In the sample code sent me, you see a joint constructed like this:
var middle = new Joint({
  minPos: 70,
  maxPos: 220,
  pin: 6,
  range: [60,150]
});

The range is quite important, this is where you specify the range of motion in degrees of the servo.  The servo above is being set to 60 degrees minimum, 150 degrees maximum.
minPos, maxPos - These define the minimum and maximum value for the leap property that is being used to move this servo.  For instance, in the code above, you can see the minPos and maxPos values being set to 70 and 220. 70 and 220 are values you'll be getting from the leap device for whatever part/property of the hand you choose. In the example, the palm's height is being used:
middle.move(frame.palmPosition.y);

Remember that middle is a Joint, and here you see that from the frame data, the palmPosition Y value is being passed to the joint move function.  What happens to the value passed into middle.move?
var _move = function(pos, constraint) {
  var angle;
	if (constraint) {
		pos = constraint(pos);
	}
	angle = _scale(pos);
	_servo.move(angle);
};

You can see that without a second argument, the call to move basically just calls scale(pos) and stores the value.
Let's see what scale does:
var _scale = function(pos) {
    if (pos<minPos) {
    	pos = minPos;
    }
    else if (pos>maxPos) {
    	pos = maxPos;
    }
    return Math.floor(five.Fn.map(pos, minPos, maxPos, _servo.range[0], _servo.range[1]));
};

This function clamps the position passed in to the minPos and maxPos values that were defined when constructing the joint.  It then interpolates the value across the min/max servo range.