# GUI usage¶

Note

This documentation currently assumes that you are using LiberTEM on a single computer. If you want to run on a cluster, please let us know by either filing an issue or by asking on our Gitter channel.

## Starting the LiberTEM server¶

LiberTEM is based on a client-server architecture. To use the LiberTEM GUI, you need to have the server running on the machine where your data is available. For using LiberTEM from Python scripts, this is not necessary, see Python API.

After installing LiberTEM, activate the virtualenv or conda environment.

You can then start the LiberTEM server by running:

(libertem) $libertem-server  By default, this starts the server on http://localhost:9000, which you can verify by the log output: [2018-08-08 13:57:58,266] INFO [libertem.web.server.main:886] listening on localhost:9000  It will then open your default web browser to this URL. There are a few command line options available: Usage: libertem-server [OPTIONS] Options: -p, --port INTEGER port on which the server should listen on -d, --local-directory TEXT local directory to manage dask-worker-space files -b, --browser / -n, --no-browser enable/disable opening the browser -l, --log-level TEXT set logging level. Default is 'info'. Allowed values are 'critical', 'error', 'warning', 'info', 'debug'. --help Show this message and exit.  New in version 0.4.0: --browser / --no-browser option is added, open browser by default. To access LiberTEM remotely, you can use use SSH forwarding. ## Connecting¶ Note The GUI is tested to work on Firefox and Chromium-based browsers for now, if you cannot use a compatible browser for some reason, please file an issue! After starting the server, you can open the GUI in your browser. If it didn’t open automatically, you can access it by default at http://localhost:9000 . At the beginning, the GUI shows a prompt to create a local cluster or connect to a running one. The number of workers is preset with a number that will likely give optimal performance on the given machine. You can also select which CUDA devices to use, if you have any (needs to have a working cupy installation). ## Starting a custom cluster¶ LiberTEM can connect to a running dask cluster. To start a cluster, first run a scheduler: (libertem)$ dask-scheduler --host localhost


GPU support in LiberTEM requires specific resource tags and environment settings on the dask workers. The easiest way to start workers with the appropriate settings is

(libertem) \$ libertem-worker tcp://localhost:8786


There are a few command line options available:

Usage: libertem-worker [OPTIONS] [SCHEDULER]

Options:
-k, --kind TEXT             Worker kind. Currently only "dask" is
implemented.
-d, --local-directory TEXT  local directory to manage temporary files
-c, --n-cpus INTEGER        Number of CPUs to use, defaults to number of CPU
-u, --cudas TEXT            List of CUDA device IDs to use, defaults to all
detected CUDA devices. Use "" to deactivate
CUDA.
-n, --name TEXT             Name of the cluster node, defaults to host name
-l, --log-level TEXT        set logging level. Default is 'info'. Allowed
values are 'critical', 'error', 'warning',
'info', 'debug'.
--help                      Show this message and exit.


New in version 0.6.0.

For a cluster setup, you can run the scheduler on the appropriate network interface and run workers on all cluster nodes to connect to the scheduler.

## Opening data¶

After connection to a cluster, LiberTEM shows a button to start browsing for available files. On a local cluster that’s simply the local filesystem.

Note

See Sample Datasets for publicly available datasets.

This opens the file browser dialogue. On top it shows the current directory, below it lists all files and subdirectories in that directory. You select an entry by clicking once on it. You can move up one directory with the “..” entry on top of the list. The file browser is still very basic. Possible improvements are discussed in Issue #83. Contributions are highly appreciated! This example opens an HDF5 file [ZMB+19].

You can also bookmark locations you frequently need to access, using the star icon. The bookmarks are then found under “Go to…”.

After selecting a file, you set the type in the drop-down menu at the top of the dialogue above the file name. After that you set the appropriate parameters that depend on the file type. Clicking on “Load Dataset” will open the file with the selected parameters. The interface and internal logic to find good presets based on file type and available metadata, validate the inputs and display helpful error messages is still work in progress. Contributions are highly appreciated!

See Loading using the GUI for more detailed instructions and format-specific information.

## Running analyses¶

Once a dataset is loaded, you can add analyses to it. As an example we choose a “Ring” analysis.

The GUI shows two windows: On the left it shows the current mask. Directly after adding the analysis, LiberTEM starts calculating an average of all the detector frames. As soon as this is finished, the average is overlaid with the mask to help the user with positioning the virtual detector. The window on the right will later show the result of applying the mask to the data. In the beginning it is empty. The first processing might take a while depending on file size and IO performance. Fast SSDs and enough RAM to keep the working files in the file system cache are highly recommended for a good user experience.

You can adjust the virtual detector by dragging the handles in the GUI. Below it shows the parameters in numerical form. This is useful to extract positions, for example for scripting.

After clicking “Apply”, LiberTEM performs the calculation and shows the result in scan coordinates on the right.

Instead of average, you can select “Standard Deviation”. This calculates standard deviation of all detector frames.

If you are interested in individual frames rather than the average, you can switch to “Pick” mode in the “Mode” drop-down menu directly below the detector window.

In “Pick” mode, a selector appears in the result frame on the right. You can drag it around with the mouse to see the frames live in the left window. The picked coordinates are displayed along with the virtual detector parameters below the frame window on the left.

If you are interested in a limited region, the ROI dropdown provides the option to select a rectangular region. For example if you select “Rect”, the average/standard deviation is calculated over all images that lie inside selected rectangle. You can adjust the rectangle by dragging the handles in the GUI.

Some analyses, such as the Center of Mass (COM) analysis, can render the result in different ways. You can select the channel in the “Image” drop-down menu below the right window.