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## Importing data

To load a simulation file from your local computer, select File → Load File from the menu or use the corresponding button in the toolbar. OVITO detects the format of the file automatically (see list of supported formats). Compressed text-based files with a `.gz` suffix can be read directly by OVITO.

The imported dataset will appear in the viewports as a new three-dimensional object and also as an entry in the "Data source" section of the pipeline editor, as indicated in the screenshot on the right.

If you select this item in the list, the "External File" panel appears below the pipeline editor. The tool buttons at the top of that panel let you reload the imported input file in case it has been changed or rewritten outside of OVITO, or you can pick a different file as data source of the data pipeline. Switching the data source file can be useful if you have set up a data analysis pipeline and now would like to apply it to a different simulation dataset.

### Command line

When launching OVITO from a terminal, you can directly specify a file to load. This works for local and remote files:

        ovito /path/filename
        ovito sftp://hostname/path/filename
        ovito https://www.website.org/path/filename

You can import several files at once by specifying multiple filenames on the command line. If they all have the same file format, they will be concatenated into a sequence forming an animatable trajectory. If they have different formats, OVITO will detect whether they represent a pair of topology/trajectory files (see next section). If not, they will be inserted as several independent objects into the scene.

### Simulation trajectories

OVITO can load trajectories consisting of a series of simulation snapshots. Various scenarios are supported by the software:

A series of snapshot files:

  By default, whenever you import a new simulation file, OVITO tries to detect if the file is part of a numbered sequence of files with similar names in the same directory. To this end, the last number (if any) in the filename you've picked is replaced with the wildcard character `*` to generate a search pattern, which will subsequently be used to look in the directory for more files belonging to the sequence. For instance, if you imported a file named `anim1c_5000.dump`, OVITO will generate the search pattern `anim1c_*.dump` to find more snapshots (e.g. `anim1c_0.dump`, `anim1c_1000.dump`, `anim1c_2000.dump`, etc). It is possible to manually override the generated file pattern in the input field highlighted in the screenshot or to turn off the automatic search by unchecking the "auto-generate" box.

One file containing all trajectory frames:

  OVITO automatically detects whether the imported file contains more than one simulation frame and loads all of them as an animation sequence. For some file types, e.g. XYZ and LAMMPS dump, this is indicated by the Contains multiple timesteps checkbox highlighted in the screenshot. Note that OVITO typically keeps only the data of a single frame in memory at a time. Subsequent frames are loaded into memory only when needed, for example if you play back the animation or move the time slider.

A pair of topology and trajectory files:

  Some MD simulation codes use separate files for the topology and the trajectory of a molecular structure. The topology file contains the static definition of atoms, bonds, etc. while the trajectory file contains the computed trajectories and other time-dependent data generated in the MD simulation. In such a case you should pick both files in the file selection dialog and import them simultaneously. OVITO recognizes automatically which of the file is the topology file and which one is the trajectory file based on the following table:

  Topology file format | Trajectory file format
  --- | ---
  LAMMPS data | LAMMPS dump
  Gromacs GRO | Gromacs XTC
  CASTEP cell | CASTEP md/geom
  any other supported format | XYZ

  The topology file will be loaded first (e.g. a LAMMPS data file) and a Load trajectory modifier will be inserted into the data pipeline to load the time-dependent atomic positions from the trajectory file (e.g. a LAMMPS dump file). This modifier merges both pieces of information -the static topology and the dynamic trajectory data- into a single animated dataset.

OVITO will display a timeline and a time slider at the bottom of main window if a simulation sequence with more than one frame was loaded. Learn more about OVITO's animation functions in this section of the manual.

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