Module Contents

ifcopenshell.api.sequence.assign_lag_time.assign_lag_time(file, rel_sequence=None, lag_value=None, duration_type='WORKTIME') None

Assign a lag time to a sequence relationship between tasks

A task sequence (e.g. finish to start) may optionally have a lag time defined. This is a fundamental concept in construction scheduling. The lag is defined as a duration, and the duration is typically either calendar based (i.e. follows the working times and holidays of the calendar) or elapsed time based (i.e. 24/7).

A sequence may only have a single lag time defined. Negative lag times are allowed.

  • rel_sequence (ifcopenshell.entity_instance) – The IfcRelSequence to assign the lag time to.

  • lag_value (str) – An ISO standardised duration string.

  • duration_type (str) – Choose from WORKTIME for the associated calendar-based lag times (this is the most common scenario and is recommended as a default), or ELAPSEDTIME to not follow the calendar. You may also choose NOTDEFINED but the behaviour of this is unclear.


The newly created IfcLagTime

Return type:



# Let's imagine we are creating a construction schedule. All tasks
# need to be part of a work schedule.
schedule = ifcopenshell.api.run("sequence.add_work_schedule", model, name="Construction Schedule A")

# Let's imagine a root construction task
construction = ifcopenshell.api.run("sequence.add_task", model,
    work_schedule=schedule, name="Construction", identification="C")

# Let's imagine we're doing a typically formwork, reinforcement,
# pour sequence. Let's start with the formwork. It'll take us 2
# days.
formwork = ifcopenshell.api.run("sequence.add_task", model,
    parent_task=construction, name="Formwork", identification="C.1")
time = ifcopenshell.api.run("sequence.add_task_time", model, task=formwork)
ifcopenshell.api.run("sequence.edit_task_time", model,
    task_time=time, attributes={"ScheduleStart": "2000-01-01", "ScheduleDuration": "P2D"})

# Now let's do the reinforcement. It'll take us another 2 days.
reinforcement = ifcopenshell.api.run("sequence.add_task", model,
    parent_task=construction, name="Reinforcement", identification="C.2")
time = ifcopenshell.api.run("sequence.add_task_time", model, task=reinforcement)
ifcopenshell.api.run("sequence.edit_task_time", model,
    task_time=time, attributes={"ScheduleStart": "2000-01-01", "ScheduleDuration": "P2D"})

# Now let's say the formwork must finish before the reinforcement
# can start. This is a typical finish to start relationship (FS).
sequence = ifcopenshell.api.run("sequence.assign_sequence", model,
    relating_process=formwork, related_process=reinforcement)

# Now typically there would be no lag time between formwork and
# reinforcement, but let's pretend that we had to allow 1 day gap
# for whatever reason.
ifcopenshell.api.run("sequence.assign_lag_time", model, rel_sequence=sequence, lag_value="P1D")