JPL DARTS Lab Q&A - Recent questions

How do I get back missing NFS mounts?

Tue, 23 Jul 2024 17:58:27 +0000

Sometimes NFS directories will be missing from a machine, e.g., one machine may be missing /home/dartsfn while all other machines have it.

How do I clear the php cache used by our apache web server?

Thu, 14 Mar 2024 22:08:03 +0000

Sometimes our webpages display stale php output after making changes to the underlying code. How can we purge the cache?

How do I restart the GitLab elastic search?

Tue, 12 Mar 2024 18:14:21 +0000

How do I restart the GitLab PlantUML server?

Tue, 12 Mar 2024 18:10:58 +0000

How do I restart the pyam mysql server?

Wed, 31 Jan 2024 14:34:48 +0000

How can I convert a regular python script into a doctest script?

Tue, 21 Nov 2023 17:04:35 +0000

My VPN is connected but I can't access any JPL websites or machines.

Wed, 15 Nov 2023 20:07:11 +0000

How do I restart the svn server?

Fri, 27 Oct 2023 14:24:01 +0000

How do I add the JPL root certificate to my laptop?

Mon, 18 Sep 2023 23:16:17 +0000

If you get insecure connections everytime you access JPL websites such as js.jpl.nasa.gov, there is a good chance you are missing the JPL root certificate.

Are there examples of integrating DARTS with MONTE for simulating autonomous navigation?

Mon, 14 Aug 2023 16:02:17 +0000

I would like to see examples of DARTS+MONTE integration for simulating autonomous navigation to a body (e.g., a moon, a planet, or a small-body asteroid).

How do I checkout a module on the main branch after saving it from a regtest sandbox?

Fri, 07 Jul 2023 20:29:28 +0000

After I pyam save from a regtest sandbox, how do I check that module out again in trunk (main) branch?

How do I check how much space I (or a Team) have left in office365 (onedrive/sharepoint)?

Fri, 07 Jul 2023 18:11:59 +0000

How do we handle loops in model data flow when using the assembly builder?

Sat, 10 Jun 2023 15:19:41 +0000

When there are loops in the model data flow, the Model.addSortingBreak() can be used to create breaks in the dataflow to get rid of loops so the model sorter can work. How do we do this when using the AssemblyBuilder since the sim.createAssemblies() method chokes when the created data flow has loops?

How can I create a complie_commands.json file for my DARTS sandbox?

Fri, 09 Jun 2023 17:30:22 +0000

Many C++ LSPs use compile_commands.json to find header/source files. How can easily build one of these for my DARTS sandbox without having to recompile everything?

How do I connect to the CAE WENG servers?

Mon, 08 May 2023 15:04:34 +0000

CAE hosts Windows servers called WENG servers. These are WIndows instances that have many of the CAE tools pre-installed. These are useful for running things like SolidWorks, which do not have Linux clients.

How do I import Python modules that use HDF5 when the DARTS libraries use a different HDF5 version?

Wed, 05 Apr 2023 22:50:31 +0000

DARTS uses a certain version of HDF5 that may differ from the versions that modules like tables use. This questions asks how we can use both of those without triggering HDF5 warnings.

How do I implemented doc tests in a Dclick file-exec script?

Thu, 16 Feb 2023 15:13:08 +0000

Scripts that are run via --file-exec from a Dclick CLI will not be __main__. Therefore, the normal doctest recipe does not work. How should this recipe be modified for a CLI file-exec script?

Is there a method for capturing a high/low watermark value for a variable and the associated time stamp?

Wed, 08 Feb 2023 18:35:51 +0000

I'm looking for a way to capture a high/low variable value with the associated timestamp, and without triggering an event?

How do I make GitLab use the full width of my screen?

Tue, 31 Jan 2023 19:15:59 +0000

If GitLab is fixed width it can be hard or impossible to see certain links. Hence, giving GitLab the ability to use your entire screen will improve your experience.

How can multiple users share a common base sandbox?

Wed, 25 Jan 2023 22:47:06 +0000

How do I add new git servers to my gpg credentials?

Tue, 24 Jan 2023 23:20:57 +0000

How do I encrypt my git credentials with gpg?

Sat, 14 Jan 2023 17:32:38 +0000

How does one get plantUML working on the gitlab server?

Fri, 13 Jan 2023 06:42:52 +0000

We use plantUML for diagrams on the gitlab server, but it seems to require its own server that dies from time to time.

How do I add a self-signed certificate to git?

Thu, 12 Jan 2023 15:30:43 +0000

How do I deliver a DSENDS package as a github repo?

Thu, 01 Dec 2022 00:33:31 +0000

How do I query part geometries and turn their visibility off?

Wed, 02 Nov 2022 02:06:06 +0000

How can I share a remote terminal session with other developers?

Fri, 28 Oct 2022 14:12:30 +0000

During development, it is often useful to be able to share a terminal session with remote developers to help with debugging. While a shared VNC session gives us full such support, sometimes vnc is not an available option. Are there other light weight alternatives?

How do I model a spacecraft bus with two solar arrays connected by a flexible hinge

Thu, 08 Sep 2022 15:25:26 +0000

I have a spacecraft that I model as a rectangular bus with two large solar panels. I want to allow the joint to be flexible and have been looking at using the SpringDamperMotor model.

I essentially want to have a flexible 'BALL' joint, meaning the joint can flex up/down and left/right, along with twist.

Is there an example of this? I think the SpringDamperMotor model is a single-axis motor (all the examples are 'PIN' joints and robot arms), is there an example of a more complicated flexible joint?

How does one profile C++ code called from a Python script?

Wed, 17 Aug 2022 17:28:52 +0000

cProfile can be used to profile Python code, but this will only get the Python functions, it will not reach into the underlying C++ functions and profile them as well. Oftentimes, we set up simulations and then want to profile something like the step or advanceTimeBy calls, which are conveniently made through Python, though we really care about profiling the C++ code underneath.

How do I set up VSCode to start working with a DARTS sandbox?

Mon, 04 Jul 2022 15:53:44 +0000

Visual Studio Code (or VSCode) is a code editor used by some developers who work with DARTS sandboxes. Like other editors, it supports syntax highlighting, intelligent code completion, snippets, code refactoring, and many other features through extensions.

How can edit and modify the contents of an HDF5 file?

Sat, 25 Jun 2022 02:24:43 +0000

How do I convert GitLab flavored markdown to a PDF?

Fri, 24 Jun 2022 21:37:26 +0000

Oftentimes, we want to convey some of the information in a GitLab issue to others, and a PDF is a useful format to be able to do that.

How do I set up my non-JPL account on the dartsgitlab.jpl.nasa.gov site?

Mon, 20 Jun 2022 12:36:35 +0000

What is the process for setting up TFA etc?

How do I convert Markdown to Asciidoc?

Tue, 24 May 2022 22:01:41 +0000

How can I trigger deprecation warnings for a module variable?

Mon, 16 May 2022 20:12:03 +0000

How do I get plugins for my Unreal Engine project despite me running Linux?

Sat, 07 May 2022 01:06:41 +0000

Since we get plugins through the Epic Games store, we can't get plugins directly while using linux.

Instead, use your PC or Mac to get Epic Games Launcher and Unreal Engine. Buy various plugins and install them to either the engine or a project. Sometimes these plugins might add functionality or they may add art assets.

In the case that they add functionality, they will install themselves directly into the engine or your plugins folder.

If they install to the Engine, you need to navigate to the Engine plugins folder and find the folder with your plugins name and copy it into the linux Engine.
If they install to the project itself, in your project directory look for a folder called "plugins" and copy that folder into your linux unreal project.

In the case that they add art assets, they might either install itself into the engine or project, if so look above for how to deal with it.

If it imports art assets into your project (or makes its own), just copy that project into linux, open the project up using the linux unreal engine and migrate the files into the Unreal Engine project you're working in (i.e. UnrealDarts)

Warning! Migrating assets between projects may mess up your file hierarchy, so after you get your wanted assets be sure to move them (in the Unreal Engine) into their proper place. After moving it be sure to right-click the top-level Contents folder and "Fix up redirectors".

Also, every month Epic Games releases a bunch of free plugins. These plugins range from sound effects to art assets and programmed feature packs (like an inventory system). Might be something to check every month as these plugins can be very high quality.

How can I determine which events in the FSM have triggered and which have not?

Wed, 04 May 2022 17:16:30 +0000

Want to write a python method that can be used during the execution of the simulation that monitors which events have triggered and which have not. This would include querying for a specific event, not just all of them.

How do I use UnrealScene for development?

Tue, 03 May 2022 17:33:22 +0000

What is the project?

The UnrealScene module consists of two parts:

UnrealDARTS: this is the Unreal Engine project which takes in a bunch of JSON parameters.
UnrealScene: this is the interpreter between DARTS and the visualizer (Unreal Engine).

This guide will discuss how to work with UnrealDARTS.

Prerequisites and FYIs

Make sure you have UnrealScene installed and setup!

Prior to working with Unreal Scene, be sure to learn how to use Unreal Engine. There are plenty of tutorials out there for Unreal Engine, and although most of them (as of this writing) are in Unreal 4 everything taught in Unreal 4 applies to Unreal 5. Here's a good introductory playlist for Unreal C++ which I used occasionally.

Be able to take advantage of Unreal Engine's blueprint capabilities and write your code so it can communicate to blueprints. Besides the blueprint debugger, you will have no debugger. No GDB, No Rider debugger, No LLDB. So it is crucial to write your code such that it meshes nicely with blueprints. If your C++ doesn't work and you don't know why rewrite the function in blueprints and debug it through blueprints.

You also want to use Rider for UE as your IDE. Among other things, it will have IntelliSense, access to Unreal's output log (which you will be using A LOT), and source control capabilities. This will make your life easier and save everyone's time. Don't bother with VS Code as it won't recognize Unreal Engine libraries.

Getting into the nitty-gritty

Now that you have the engine opened up, in the content browser/drawer go into /Content/.

Notice the following folders:

_UI,
- Contains all UI/HUD elements that we are using. If you make anymore UI elements put them there and don't clutter up the working directories.
_Blueprints:
- Contains all blueprint related logic.
Maps :
- EditorStartup which is the batch mode map (think of this as production map)
- Contains DemoTest which is the test map where development work gets done.
Assets:
- Art assets such as 3D models, materials will live here.
- If you ever plan on doing Nanite work in Unreal Engine, be aware that currently, Nanite doesn't support real time mesh importation, so you'll need to import Nanite meshes in this folder.

In /Content/Blueprints there is BP_SceneManager which devices from SceneManager.cpp/h. This is the final product that lives in EditorStartup. BP_SceneManager_ForTesting is what you will be using for test code and blueprints debugging. BP_UnrealSceneViewer is the camera that flies around the scene and is what contains logic to interact with UI.

The BP_SceneManager has a Debug bool exposed to blueprints, tick this to be true if you want to Log all output to the output log.

I suggest not using PrintToScreens as these are temporary and don't log to the output log, and thus are useless for any long debugging sessions.

The UI

If you press 3, the UnrealScene taskbar will appear. You have three options:

Loading (floppy with up arrow)
Saving (floppy with down arrow)
Clearing scene (Trash can)

Loading and Saving both look in the directory in UnrealScene/Saves for files. It assumes the files are in JSON format and contain the commands.

To load and save, input the name of the file (along with its type, i.e., txt) and press the load/save button.

Why you should care about Saving and Loading

(hint it saves you time hint)

Saving test cases and then loading them up in the future will allow you to analyze parsed commands more efficiently without looking at long and confusing output logs, can allow you to easily tweak save files, and can help you make your own test cases from existing ones without dealing with python.

When using the load with the clear button you can test more scenes in a single editor session.

I need a frame that is always located at the CM but is fixed to the body

Thu, 21 Apr 2022 00:20:30 +0000

I need a frame that is always located at the center of mass of the main body but which is also fixed relative the body frame. I thought simObj.mbody().cmFrame() would do this, but it seems like it's fixed relative to the pcr frame. Will "CapsuleBase_obj103_cm_frame" or "cegraph_cm_frame" give me what I'm looking for? I can also create one, but it's not clear to me how to create one that has both of these properties (i.e. always at the cm and rotates with the body).

If the answer is CapsuleBase_obj103_cm_frame, then will the object number of this frame always be the same?

How do I improve exceptions thrown by SWIG directors?

Wed, 20 Apr 2022 18:00:03 +0000

The default exceptions thrown by SWIG directors can be nearly useless at times, since they do not show the Python stack trace by default.

What are options for performing convex decomposition in DARTS, and how do they differ?

Tue, 05 Apr 2022 15:39:43 +0000

Convex decomposition is a crucial part of efficient and accurate collision detection for arbitrary geometries in Bullet. What options are there in DARTS, and how do they differ?

How do I redirect C-level streams in Python?

Mon, 04 Apr 2022 21:01:11 +0000

Python's contextlib comes with a "redirect_stdout" method for redirecting Python streams to variables. However, this does not work for C-level streams. How can this be done for C-level streams as well?

What are good practices for setting up a Kanban board on gitlab?

Fri, 01 Apr 2022 14:32:21 +0000

Kanban boards are effective tools for managing software development for projects. What are suggested practices in keeping with the way the DARTS Lab gitlab issues, projects and labels are organized?

What are dlopenflags?

Tue, 29 Mar 2022 18:07:51 +0000

DARTS uses dlopenflags to control module import behavior. What are they and how do we use them? This questions also lists some strange corner cases.

How do I generate a terrain using simplex noise?

Fri, 18 Mar 2022 22:27:38 +0000

Simplex noise is a common technique for generating semi-realistic looking terrain. An article that uses this plus other techniques to generate complex terrains is shown here. How can we make use of this technique in DARTS to quickly generate terrains?

Given a tar ball on a telerbotics machine, How do you copy and run it on nexus?

Thu, 17 Mar 2022 19:33:57 +0000

after building a nexus compatible tar ball package, what steps should be taken to run the code on nexus?

How do I visualize a DAT file?

Tue, 08 Mar 2022 20:24:45 +0000

What does a "stiff" system mean?

Mon, 07 Mar 2022 17:58:22 +0000

How does one install/use RealVnc Viewer on your computer?

Tue, 25 Jan 2022 19:35:04 +0000

going to answer this right now.

How do I correctly manipulate Python objects from C++ if threads are enabled in the swig wrapper creation?

Wed, 19 Jan 2022 23:03:20 +0000

This question pertains manipulating objects directly in your C++ source code, e.g., with calls like `Py_DECREF` (not the swig-generated wrappers, which should have what is described in the answer taken care of for you).