Navigation stack with GPS and without wheel encoders

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Hi, I was working with navigation stack on a rover. It was equiped with wheel encoders, GPS, IMU and a LIDAR. As I have goos localization sensors I remove ACML and instead I used robot_localization with 2 EKF, one for map->odom and the oder for odmo->base_link. Everithing works ok. But now I need to do the same on a boat and on a UAV. Both of them have nor wheel encoders. So, is there a way to work with navigation stack, in order to waypoint navigation while avoid local obstacles? BTW, I use an empty static map and NS was used for global path planning and local obstacles avoidance.

EDIT: Both, UAV and ASV have IMU sensor. They have a good map->base_link estimate using GPS and IMU. The problem is how to get a good odom->base estimate without wheel encoder.

Thank!