True scale tacking and mapping using downward looking camera and rangefinder

[Razbotics]

According to algorithm the median scene depth is calculated and used for scale. I want to know if we can replace median scene depth with measurements from rangefinder and obtain true scale tracking and mapping. In this below reference here is the region where median scene depth is calculated is this the correct region for modification or more modification is needed? https://github.com/raulmur/ORB_SLAM/blob/ce199650a25653808f96b83557333bce3461d29f/src/Tracking.cc#L439 It will be really appreciated if I get some help for the modifications.