The main features of fogleman/hmm are: Low Level Geospatial Libraries.
Open-source alternatives to fogleman/hmm include: appelmar/gdalcubes — Creating and analyzing Earth observation data cubes in R. carlren/gslicr — gSLICr: Real-time super-pixel segmentation. connormanning/entwine — Entwine - point cloud organization for massive datasets. cosmiq/yolt — You Only Look Twice: Rapid Multi-Scale Object Detection In Satellite Imagery. davidfrantz/force. ahhz/raster — C++ library for geographical raster data analysis.
Entwine - point cloud organization for massive datasets