Visualization

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Software Available

We have installed the latest versions of the open source visualization suites: VMD, VisIt and ParaView.

Notice that for using ParaView you need to explicitly specify one of the mesa flags in order to avoid trying to use openGL, i.e., after loading the paraview module, use the following command:

 paraview --mesa-swr

Notice that Niagara does not have specialized nodes nor specially designated hardware for visualization, so if you want to perform interactive visualization or exploration of your data you will need to submit an interactive job (debug job, see [[1]]). For the same reason you won't be able to request or use GPUs for rendering as there are none!

Interactive Visualization

Runtime is limited on the login nodes, so you will need to request a testing job in order to have more time for exploring and visualizing your data. Additionally by doing so, you will have access to the 40 cores of each of the nodes requested. For performing an interactive visualization session in this way please follow these steps:

  1. ssh into niagara.scinet.utoronto.ca with the -X/-Y flag for x-forwarding
  2. request an interactive job, ie.
  3.   debugjob
    

    this will connect you to a node, let's say for the argument "niaXYZW"

  4. run your favourite visualization program, eg. VisIt/ParaView
  5.   module load visit
      visit
    
      module load paraview
      paraview --mesa-swr
    
  6. exit the debug session.

Remote Visualization -- Client-Server Mode

You can use any of the remote visualization protocols supported for both VisIt and ParaView.

Both, VisIt and ParaView, support "remote visualization" protocols. This includes:

  • accessing data remotely, ie. stored on the cluster
  • rendering visualizations using the compute nodes as rendering engines
  • or both

VisIt Client-Server Configuration

For allowing VisIt connect to the Niagara cluster you need to set up a "Host Configuration".

Choose *one* of the methods bellow:

Niagara Host Configuration File

You can just download the Niagara host file, right click on the following link host_niagara.xml and select save as... Depending on the OS you are using on your local machine:

  • on a Linux/Mac OS place this file in ~/.visit/hosts/
  • on a Windows machine, place the file in My Documents\VisIt 2.13.0\hosts\

Restart VisIt and check that the niagara profile should be available in your hosts.

Manual Niagara Host Configuration

If you prefer to set up the verser yourself, instead of the configuration file from the previous section, just follow along these steps. Open VisIt in your computer, go to the 'Options' menu, and click on "Host profiles..." Then click on 'New Host' and select:

Host nickname = niagara
Remote host name = niagara.scinet.utoronto.ca
Username = Enter_Your_OWN_username_HERE
Path to VisIt installation = /scinet/niagara/software/2018a/opt/base/visit/2.13.1

Click on the "Tunnel data connections through SSH", and then hit Apply!

Visit niagara-01.png


Now on the top of the window click on 'Launch Profiles' tab. You will have to create two profiles:

  1. login: for connecting through the login nodes and accessing data
  2. slurm: for using compute nodes as rendering engines

For doing so, click on 'New Profile', set the corresponding profile name, ie. login/slurm. Then click on the Parallel tab and set the "Launch parallel engine"

For the slurm profile, you will need to set the parameters as seen below:


Visit niagara-02.png Visit niagara-03.png


Finally, after you are done with these changes, go to the "Options" menu and select "Save settings", so that your changes are saved and available next time you relaunch VisIt.

ParaView Client-Server Configuration

Similarly to VisIt you will need to start a debugjob in order to use a compute node to files and compute resources. Here are the steps to follow:

  1. Launch an interactive job (debugjob) on Niagara,
  2.  debugjob
    
  3. After getting a compute node, let's say niaXYZW, load the ParaView "offscreen" module and start a ParaView server,
  4.  module load paraview-offscreen/5.6.0
     pvserver --mesa-swr-avx2
    

    The --mesa-swr-avx2 flag has been reported to offer faster software rendering using the OpenSWR library.

  5. Now, you have to wait a few seconds for the server to be ready to accept client connections.
  6.  Waiting for client...
     Connection URL: cs://niaXYZW.scinet.local:11111
     Accepting connection(s): niaXYZW.scinet.local:11111
    
  7. Open a new terminal without closing your debugjob, and ssh into Niagara using the following command,
  8.  ssh YOURusername@niagara.scinet.utoronto.ca -L11111:niaXYZW:11111 -N
    

    this will establish a tunnel mapping the port 11111 in your computer (localhost) to the port 11111 on the Niagara's compute node, niaXYZW, where the ParaView server will be waiting for connections.

  9. Start ParaView on your local computer, go to "File -> Connect" and click on 'Add Server'. You will need to point ParaView to your local port 11111, so you can do something like
  10. name = niagara
    server type = Client/Server
    host = localhost
    port = 11111
    

    then click Configure, select Manual and click Save.

  11. Once the remote server is added to the configuration, simply select the server from the list and click Connect. The first terminal window that read Accepting connection... will now read Client connected.
  12. Open a file in ParaView (it will point you to the remote filesystem) and visualize it as usual.

Multiple CPUs

For performing parallel rendering using multiple CPUs, pvserver should be run using mpiexec, ie. either submit a job script or request a job using

 salloc --ntasks=N*40 --nodes=N --time=1:00:00
 module load paraview-offscreen/5.6.0
 mpiexec pvserver --mesa-swr-avx2

Final Considerations

Usually both VisIt and ParaView require to use the same version between the local client and the remote host, please try to stick to that to avoid having incompatibility issues, which might result in potential problems during the connections.

Batch mode and Scripting

Both, VisIt and ParaView, allow for batch processing using scripting in different languages.

VisIt

In order to run or launch the Python interpreter for VisIt, you will need to execute the following command:

visit -cli -no-win -norun engine_par

the 'engine_par' flag is needed in order to run the visualization engine in parallel.


In order to execute scripts in batch mode, use the following command:

visit -cli -no-win -norun engine_par -s scriptName.py

Notice that for running in parallel, in addition to loading the VisIt module, an mpi module should also be loaded. Eg.

  module load visit
  module load intel/2018.2 intelmpi/2018.2 


Alternatively, if one wants to assign resources from the cluster just from within the script one should add the following line to the script

  OpenComputeEngine("localhost", ("-l", "srun", "-np", "40"))


References:
https://www.visitusers.org/index.php?title=ParallelPorting#Making_sure_you_actually_have_a_parallel_engine
https://www.visitusers.org/index.php?title=VisIt-tutorial-Python-scripting
https://www.visitusers.org/index.php?title=Python_examples
https://www.visitusers.org/index.php?title=VisIt-tutorial-Advanced-scripting

ParaView

ParaView offers a python interpreter pvbatch to use

pvbatch --mesa-swr-avx2 --force-offscreen-rendering scriptName.py


References:
https://www.paraview.org/Wiki/ParaView_and_Batch
https://www.paraview.org/Wiki/ParaView/Python_Scripting

Other Versions

Alternatively you can try to use the visualization modules available on the CCEnv stack, for doing so just load the CCEnv module and select your favourite visualization module.