Database
[{"direction":135,"latitude":-3.744851,"longitude":-38.545571,"metrictimestamp":"20180201025959","odometer":55697826,"routecode":0,"speed":3,"deviceid":134680,"vehicleid":32040},{"direction":135,"latitude":-3.744851,"longitude":-38.545571,"metrictimestamp":"20180201025959","odometer":55697826,"routecode":0,"speed":3,"deviceid":134680,"vehicleid":32041},{"direction":345,"latitude":2.744851,"longitude":28.545571,"metrictimestamp":"20180201025959","odometer":100,"routecode":1,"speed":32,"deviceid":0,"vehicleid":32040},{"direction":123,"latitude":1.744851,"longitude":18.545571,"metrictimestamp":"20200201025959","odometer":110,"routecode":11,"speed":132,"deviceid":1,"vehicleid":32040},{"direction":12311,"latitude":11.744851,"longitude":118.545571,"metrictimestamp":"20200501025959","odometer":1101,"routecode":111,"speed":11,"deviceid":11,"vehicleid":32040}]
Query
db.collection.aggregate([{$addFields:{date:{$toInt:{$substrBytes:["$metrictimestamp",0,8]}}}},{$group:{_id:{vehicleid:"$vehicleid",date:"$date"},count:{$sum:1}}}])