code: private int groupIndexForPoint(int pointIndex) {
  		if (this.pointCoordinates == null || pointIndex < 0 || pointIndex >= this.pointCoordinates.length) {
  			throw new IndexOutOfBoundsException();
  		}
  
  		if (this.partIndexes == null) {
  			return 0;
  		}
  
  		for (int i = 0; i < this.partIndexes.length; ++i) {
  			if (pointIndex < this.partIndexes[i]) {
  				return i;
  			}
  		}
  
  		return this.partIndexes.length;
  	}
docs: Replies the group index inside which the point is located at the specified index.
  
  @param pointIndex is the global index of the point.
  @return the index of the group.
  This value is between <code>0</code> and <code>this.getGroupCount()</code>
  @throws IndexOutOfBoundsException in case of error.