As we prepare to migrate our current LabVIEW groundstation from ArduPilot to supporting ArduPilot Mega, we're taking the opportunity to rethink its architecture and code base.
Right now it's written in LabVIEW, a visual programming environment that has the advantage of rapid development and easy-to-make instrument displays, as well as being cross-platform. But the problem with it is that the development tools aren't free (indeed, the ones that can create an executable file start at $1,249!), and distributing the files requires users to download a runtime engine and serial driver. As a result, we don't have as much community participation in the ground station as we do in most of our other projects.
Over the past year, we've been looking for an alternative with free and good development tools. It needs to be cross-platform, compatible with open source code standards, and appropriate for a ground station (ie, able to handle a rich visual environment and to talk directly with the serial port). Eventually a good candidate emerged in Nokia's Qt application and UI framework, and I'd like to present it here for community feedback.
You can see a glimpse of Qt above, but here's the description from the site:
"Qt is a cross-platform application and UI framework. Using Qt, you can write web-enabled applications once and deploy them across desktop, mobile and embedded operating systems without rewriting the source code.
Features
- Intuitive C++ class library
- Portability across desktop and embedded operating systems
- Integrated development tools with cross-platform IDE
- High runtime performance and small footprint on embedded"
Note that it's cross platform on more than just computers--it will also run on phones, too, which introduces the possibility of an ArduPilot GCS on Android or some other smartphone, which would be very cool. Also, we intend to integrate the current ArduPilot configuration utility into the GCS, so one desktop program can handle all the ArduPilot functions, from mission planning to real-time data display, including integrated Google Earth and video handling and image processing.
So what do you think? Is this a good code foundation for a full-featured groundstation? Does Qt look like something you'd adopt for the right project?
[UPDATE: See this Swiss team's MAV groundstation for an example of what Qt can do. Nice! It's open source, so we can build on it if we want.]
Comments
"In general I think your readers are right that Python is a way easier choice and that more people will be able to contribute that way.
However I think that the discussion has ben led away from the right focus: It is not the question, wether Python or C/C++ is easier to learn and handle. It is also not the question how many developers exist for each language.
Because eventually the development will be carried out by a small group of 2..5 enthusiastic developers, not dozens of people of the community. The reason for this is quite simple: A ground control station with significant functionality will require time to understand the basic structure and concepts (independent of the choice of language and toolkit) and only few people will be willing to invest that.
The questions are merely, like in any application development:
- What does the use case require (What is the best toolkit and programming language)
- What is a user, what is a developer?
- What are the requirements of users?
- What are the requirements of developers?
I have also some guesses on the answers:
- The use case requires complete operating system abstraction. It requires a really, really good UI toolkit with hardware acceleration through OpenGL (HUD rendering on CPU is just too slow). It should also support multithreading
- My educated guess: 95% of ArduPilot users will not want to touch the GCS code at all, so we are looking at 95% pure-users and 5% more intense developers
- Users want: Easy deployment (download an executable and double-click it, no additional libraries, no compiling of code), Low hardware requirements, and then implementation, not language specific stuff like look and feel, good interaction concepts, etc.
- Developers want: Clean separation of individual UI parts, separation of communication and visualization layers, assistants for UI elements like forms, an object oriented general setup and multithreading support (critical for using serial, OpenGL and still having a responsive UI).
In general Python and C++ fulfill all these requirements, except that deployment for Python applications on Windows requires to install the whole toolkit or to pack the python code into an C/C++ executable with in-built interpreter. Now many points are not that new or surprising, but some things are worth to notice:
- Because of the hardware access to serial and OpenGL interfaces, implementing this kind of application is not trivial, because it involves multithreading and requires careful implementation. This eventually implies that it will require either significant time to learn these concepts or a computer science background
- These requirements imply "experts" either by profession or interest. Those experts typically prefer an object oriented architecture and are, if they come from the application development domain, usually trained in C/C++ or Java (because those applications can be deployed easily on Windows). Of course any of them can pick up Python quickly, if he/she doesn't know it already as well.
To conclude, I would say the more important concerns should be to select a language and toolkit that supports multithreading, OpenGL hardware acceleration, object oriented programming and easy deployment. I think it is pretty clear that Qt is the right toolkit. Now C/C++ vs Python will more depend on what developers prefer and how well the deployment with py2exe works in practice.
Our decision to go with C/C++ was eventually driven by the easier deployment in Windows and the fact that our developers here write C/C++ code on the MCU and single board computer and thus can easily understand the ground control station code."
Earl
- It has the biggest developper's community
- It is truely cross-platform ( You could also have a J2ME flavor for mobile devices)
- There are loads of very good free IDEs available (eclipse, netbeans, ...)
- There are a lot of open source libraries available ( 3d graphics, 2D graphs,...)
- It is much simpler/safer to program than C++
- It could run as a tool in processing This would be useful during dev phases.
- I don't believe garbage collection would be an issue for a GCS if it is reasonably well designed. At least not on most today's PC.
Has I said previously I am working on a small prof of concept using only html 5 to render the GCS UI and Java on the webserver side. But don't worry there are several lightweight opensource webservers that can be used to implement the communication with aircraft. I am very confident that it can be done.
HTML 5 is already supported by several browsers and it will take off very quickly in the next 12 months.
Is there currently a set of requirements for an Ardupilot ground station software? Maybe we should get the community to collate some generic implementation independent requirements to determine what are some desired features. We'd also need to get strategic direction from Chris/Jordi to ensure that requirements are in line with Ardupilot strategic roadmap.
I have wasted time in the past exploring a myriad of different implementation technologies before having a well defined set of requirements.
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