why rpe choose estimate result to generate paired indices

[huhumeng2]

hi, in your great tools, in found in line: https://github.com/MichaelGrupp/evo/blob/2361a018213823c518798e518fbc084d2d942f73/evo/core/metrics.py#L253

i see use estimate trajectory to generate id pairs, but estimate tracjectory sometime not right, and when we compare VO/VIO algorithm performance, use different estimate result to do evaluate is not in a same metric, so is here some other reason to use estimate result to generate paired indices

[MichaelGrupp]

You are right, it might be good to allow switching this behavior if needed. I think I should add an option to change this from the current default behavior.