A question about the initial value of Rs[j]

[KleistvonLiu]

First, thanks for the great project!!
I have a question about about the initial value of Rs[j]. In processIMU() we have Rs[j] *= Utility::deltaQ(un_gyr * dt).toRotationMatrix(); to update Rs[j]. I think the initial value of Rs[j] should be the end value of Rs[j-1], since Rs should be in reference frame. But I didn't find such code about initialization, I am very confused.