The difference and contact between EKF and EKF2

1

Recently started learning px4firmware, when I see the folder EKF， I have a headache!! Please tell me the contact and difference between EKF and EKF2.
Thank you!

2

do you know it now?
i am learning it ,and it is a little hard for me as well~!

3

You may have a look at
http://ardupilot.org/copter/docs/common-apm-navigation-extended-kalman-filter-overview.html

4

EKF2 is not very simple to understand as a big math lies in background. The importance of EKF2 of PX4 is making low cost IMUs and sensors available for airborne systems by prediction and observation techniques and sensor fusion techniques to reject low confidence data over high confidence data.

You may have a look at https://www.researchgate.net/publication/277143039_Recursive_Attitude_Estimation_in_the_Presence_of_Multi-rate_and_Multi-delay_Vector_Measurements/download