An autonomous tying assembly wherein the improvement comprises a gantry subassembly comprising a bridge member for laterally spanning, in use, a selected section of a work site, and a gantry drive motor for effecting travel of the gantry subassembly along a first path of the selected section of the work site; a carrier subassembly movably mounted on the gantry subassembly and comprising a carriage and a carriage drive motor for effecting travel of the carriage along a second path along the span of the bridge member; a tool actuation subassembly mounted on the carrier subassembly comprising a motion actuator, an end-effector operatively connected to the motion actuator, and a tool actuation drive motor for effecting travel of the end-effector along a third path generally perpendicular to the second path; and, characterised by further comprising: an autonomous control system comprising a perception subsystem configured to receive, interpret, and communicate three-dimensional image data, a motion planning subsystem configured to receive the data from at least the perception subsystem to calculate and communicate travel instructions comprised of direction, extent and speed of travel of one or more of the gantry subassembly , carrier subassembly , and tool actuation subassembly on the first, second and third paths, respectively, and a motion control subsystem configured to receive at least travel instructions from the motion planning subsystem and to effect the calculated travel instructions by operative control of at least one of the gantry drive motor , the carriage drive motor and the tool actuation drive motor . a gantry subassembly comprising a bridge member for laterally spanning, in use, a selected section of a work site, and a gantry drive motor for effecting travel of the gantry subassembly along a first path of the selected section of the work site; a carrier subassembly movably mounted on the gantry subassembly and comprising a carriage and a carriage drive motor for effecting travel of the carriage along a second path along the span of the bridge member; a tool actuation subassembly mounted on the carrier subassembly comprising a motion actuator, an end-effector operatively connected to the motion actuator, and a tool actuation drive motor for effecting travel of the end-effector along a third path generally perpendicular to the second path; and, characterised by further comprising: an autonomous control system comprising a perception subsystem configured to receive, interpret, and communicate three-dimensional image data, a motion planning subsystem configured to receive the data from at least the perception subsystem to calculate and communicate travel instructions comprised of direction, extent and speed of travel of one or more of the gantry subassembly , carrier subassembly , and tool actuation subassembly on the first, second and third paths, respectively, and a motion control subsystem configured to receive at least travel instructions from the motion planning subsystem and to effect the calculated travel instructions by operative control of at least one of the gantry drive motor , the carriage drive motor and the tool actuation drive motor . <EOS>