GPS alt and barometers alt

[supers...@vip.qq.com]

hi.Im from China so my english is not well...

Im developing a new multirotor controller.I use a kalman filter to get altitude and vertical velocity.When I hold alt only with barometer,it works well in indoor environment.But really bad when I fly outdoors.

First, wind is a very important factor that can cause the plane cant hold well and i cant find a solution.

Second,when I fly fast or I stop suddenly, the plane perform a height drops ( drops lower when i fly faster ,and back to its original alt when it stop ),I really dont know why...

I heard that GPS is notoriously less accurate than baro, but when I use GPS alt instead of baro alt,these two problems is solved,though i cant hold really well when i use gps alt(but i think its much better than baro alt hold, i can fly very fast without height drops )

So im finding a solution to combine baro alt and gps alt. Is there some kind of code in ardupilot do the similar things?thanks very much!