IsTracked fires alternately with true and false in didUpdate of ARKit.

Hello.

I now implement video display from image detection. I'm worried there.

I'm looking for this movement of ARImageTrackingConfiguration.

2019-11-28 17:45:00.645012+0900 arkitVideo[6100:3600050] Metal GPU Frame Capture Enabled
2019-11-28 17:45:00.645430+0900 arkitVideo[6100:3600050] Metal API Validation Enabled
####### isTracked= true
####### isTracked= true
####### isTracked= true
####### isTracked= true
####### isTracked= true
####### isTracked= true
####### isTracked= false

However, ARWorldTrackingConfiguration will be like this.

2019-11-28 17:52:19.918561+0900 arkitVideo[6201:3602382] Metal GPU Frame Capture Enabled
2019-11-28 17:52:19.918803+0900 arkitVideo[6201:3602382] Metal API Validation Enabled
####### isTracked= true
####### isTracked= false
####### isTracked= true
####### isTracked= false
####### isTracked= true
####### isTracked= false

I want to get movement like ARImageTrackingConfiguration with ARWorldTrackingConfiguration.