Tom right description wrong name it is a Tamper. Probably a Jackson 6700 or similar. A Harsco Tamper Mark III equivalent. The ballast regulator pictured by Genoz moves the stone around after the tamper does it's job. after several passes to line and level the track the regulator will lead with it's broom attachment and clean all the remaining stone off the ties.
Looking at the original picture above note the stone is dropped level to the top of the rail nice and smooth. When the Tamper comes through it lines and levels the track. This is three dimensional action to line both ways. Hooks on the Tamper grab the rail and lift it as necessary and or shoves it left or right. The machine has Tamp heads that seriously vibrate and liquify the stone allowing this action to happen. The heads then drop into the ground and its fingers squeeze the stone when they get 1 inch below the tie. It applies about 60,000 lbs of force on the stone forcing it under the tie, stabilizing the tie and track into final position. Now the stone is tightly compacted on this pass. The process for each tie is about 10 seconds. Very fast and very violent. These machines then to self destruct over time, it is one of the most expensive machines to maintain.
Look at the stone behind the machine and you will see it is almost gone, especially within one foot of the rail. The rule of thumb is one inch of raise requires 6" of stone on top or level to the top of the rail. You don't tamp the middle of the tie only within 12" in the rail. So they may line and level it flat and then make more passes building super elevation into and out of curves. The ballast cart pictured above will be brought back in and drop more stone on top, and the process starts over again. That machine could wind up working the same piece of track 6 times.
Look at the top of the machine, this is where the calculations are made. There is a Black board crossing the machine on the roof. That is exactly over top of the rail hooks, jacks and tamp heads. At the rear end of the machine are three receivers. They receive IR light from the projectors on the other end of the machine, located on the Bogie cart. (when you took the picture the cart was not extended out the 62' cord length typical used for fine tuning track.) When they are using these computers the black board will block the light to the receiver and that tells the machine to stop raising or lining the track, which is now within tolerance of 1" per 31' of track, horizontal and or vertical for the speed this track will run at. The third receiver is on the side of the machine for lining.
Newer machines I think run off of GPS and are a lot more sophisticated. The guys run back and forth over a segment of track a couple of times calculating all the rises and falls with pinpoint accuracy. they go back to the beginning set some parameters and let the computers take over and let the machine run in full auto.
Typically where ever there is a Tamper there is a Regulator close by. You can go on U Tube and see videos and time lapse video's of these beasts in action. The main lines run even larger machines that do 4 ties at once. I remember a good time lapse of a train wreck site in NY or NJ where a passenger train wrecked on a water front. They show these machines going back and forth repeatedly for days.
