Explanation of cascade.xml in a haar classifier

Question

It would be best if someone could explain the numbers/values in the cascade.xml entirely. Example in:

<!-- stage 0 -->
<_>
  <maxWeakCount>3</maxWeakCount>
  <stageThreshold>-8.8384145498275757e-001</stageThreshold>
  <weakClassifiers>
    <_>
      <internalNodes>
        0 -1 66 5.1593100652098656e-003</internalNodes>
      <leafValues>
        -8.0555558204650879e-001 8.0694979429244995e-001</leafValues></_>
    <_>
      <internalNodes>
        0 -1 108 1.5044789761304855e-002</internalNodes>
      <leafValues>
        -6.2940740585327148e-001 7.5122624635696411e-001</leafValues></_>
    <_>
      <internalNodes>
        0 -1 99 -4.7172707127174363e-005</internalNodes>
      <leafValues>
        5.5112153291702271e-001 -8.6111217737197876e-001</leafValues></_></weakClassifiers></_>

What are the meanings of these values

      <internalNodes>
        0 -1 99 -4.7172707127174363e-005</internalNodes>

Another question is, how does the program know which feature to use for a particular stage? As far as I know, features are in the form as below

<_>
  <rects>
    <_>
      21 6 3 5 -1.</_>
    <_>
      22 6 1 5 3.</_></rects>
  <tilted>0</tilted></_>

Whereby it's the coordinates of two rectangles, forming something like below:

=-=    = Black colored rectangle
=-=    - White colored rectangle
=-=
=-=
=-=

What are the values -1. and 3. mean? I know it's weights but how is it used to calculate the feature?

Summary

1. What are the meaning of the values inside <internalNodes>?
2. How is the feature calculated? How are the weights in <rects> use?
3. Most importantly, which field denotes that which features are being used in a particular stage/node.

Thanks!

Answer 1

After digging into OpenCV's source code, I finally obtain answers to my own questions.

• Values enclosed withtin internalNodes tags

node.left node.right node.featureIdx node.threshold

I'm not sure what's node.left and node.right are for as I can't see them being called anywhere.

• The weights are used to calculate the feature as in below:

float ret = rect[0].weight * CALC_SUM(p[0], _offset) + rect[1].weight * CALC_SUM(p[1], _offset);

• As mentioned in the first bullet, the node.featureIdx are the index of the feature that's being evaluated at that particular node.