If there will be measurement before the next predict, `statePost` would be assigned to updated value. So I guess these steps are meant to handle when no measurement and KF only do the predict step.
```cpp
statePre.copyTo(statePost);
errorCovPre.copyTo(errorCovPost);
```
// P'(k) = temp1*At + Q
gemm(temp1, transitionMatrix, 1, processNoiseCov, 1, errorCovPre, GEMM_2_T);
- // handle the case when there will be measurement before the next predict.
+ // handle the case when there will be no measurement before the next predict.
statePre.copyTo(statePost);
errorCovPre.copyTo(errorCovPost);