Background

MayaVi is an open source scientific data visualization tool written entirely in Python.

I started work on MayaVi in 2000. At that time, a few colleagues of mine needed to visualize their computational fluid dynamics (CFD) data but the only suitable tools available were commercial, closed source programs that were prohibitively expensive.

We looked at some open source tools as alternatives. OpenDX had just been released to the public and at that time was hard for me to get up and running. OpenDX was also a fairly complex system with a steep learning curve.

Another visualization/graphics library, VTK, was also available as open source. VTK is an extremely powerful visualization library written in C++. It is very portable and runs on various flavors of Unix, Windows, and recently on Mac OS X.

VTK was chosen as the most appropriate solution, but it was not enough to solve the problem at hand. An application was needed on top of the VTK library before non-programmers equipped only with specialized domain knowledge could sit at a computer and visualize their data.

Python Chosen

Although most of my previous experience was in C and C++, I felt that another language might be a better choice for quickly developing a graphical user interface. VTK is written in C++, but it has also been wrapped for Python, Tcl and Java. I took a look at each of those.

I ruled out Tcl because I felt Python's syntax was much cleaner and because I had heard that large Tcl programs could be hard to maintain. Java had the disadvantage of requiring compilation with each change in the code, and the ability to run code in any recent browser was of no use for this project. Java's verbose syntax as compared to Python was also a point against it. Python was just as portable as Java and a much easier to learn and use language. I'd also read the Python tutorial, seen various Python programs and liked the language very much for its simplicity, object oriented nature, dynamic data typing, and large standard library.

Starting with a few simple Python scripts using VTK, I was able to get my colleagues up and running fairly quickly with a few custom CFD visualization scripts. At this time I was still learning Python and Tkinter (the GUI toolkit used in MayaVi) and created a GUI based tool called VTK-CFD in June 2000. This went through several rounds of improvements until I eventually completely re-wrote it and released MayaVi in May 2001.

Results

MayaVi was written in 100% pure Python and by virtue of VTK, Python, and Tkinter's portability, it works on Linux, Unix, and Windows. Python turned out to be simple, easy to learn, and yet extremely powerful. Its interactive interpreter was a huge plus when learning and experimenting. It also has excellent freely available documentation.

I found the development cycle extremely fast because Python is both object oriented and interpreted. The program can be well-designed from an OO standpoint, and thus more maintainable, but there is no compilation to wait for each time you make alterations to your code.

Python's readability and dynamic typing made it even easier to write, maintain, and extend the code. I never had to worry about types, which let me focus on the problem at hand rather than wrestle with the language and its syntax. This made me much more productive than I was with C and C++. For example, I was able to write a complete VTK documentation browser with GUI and search engine in just 400 lines of code.

Flow past a cylindrical post, showing configuration dialog, VTK pipeline, and VTK documentation browser. Data courtesy of NASA. Zoom in

Excellent support for introspection, coupled with a comprehensive standard library, made it easy to write data-driven code like the vtkPipeline browser. This automatically generates a GUI at runtime that displays the VTK graphics pipeline. It also generates a GUI configuration dialog for any VTK object by parsing the object's methods with Python's regular expression module, categorizing it, and building the GUI accordingly. This code is also used in MayaVi's persistence mechanism, which can save most VTK objects to disk by inspecting them at runtime. The use of introspection to write data-driven modules such as these avoided substantial amounts of manual coding, and makes MayaVi self-extending as additional VTK objects are defined.

Since Python is a scripting language, it was the natural choice for an extension language for MayaVi. As a result, MayaVi isn't just written in Python but can also be scripted by end users working in Python, in order to extend it with additional useful functionality.

I'm not a software developer or a computer scientist. Neither am I a graphics expert. While I did have a good bit of programming experience with C/C++, I knew very little Python when I started on this project. Yet, I was able to learn Python using only its tutorial and the standard Python documentation, and then could quickly develop a substantial application. I was pleased that Python could be learned so easily and then so readily applied to non-trivial tasks.

It is important to note that this project was only a spare time activity for me, which means that I had very little sustained time to work on it. I was the sole developer and I had to write the code, maintain the web pages, write the documentation, and answer user questions all by myself.

Even so, I was able to write about 16,000 lines of Python code in the equivalent of about 4 months of full time effort and have produced a successful end product. This effort was spread over about 5 versions of VTK-CFD and 3 versions of MayaVi. MayaVi has been downloaded over 12,000 times from SourceForge, with over 3,500 downloads of the latest release in a three months time period. There are now thousands of users all over the world applying MayaVi in many research fields. It has recently been packaged for Debian Linux and was included in its latest release, Woody.

Conclusion

If it weren't for Python, MayaVi would not exist. Programming in Python is such a pleasure and so easy that even a spare time project can be very successful in doing what it set out to do. There were no major porting issues and MayaVi runs perfectly well under Linux, Unix, and Windows with very little modifications made by me. Overall it has been a wonderful experience with Python. I've learned so much, become very productive with it, and hopefully have also made others productive with the tools I have been able to write.

About the Author

Prabhu Ramachandran is an Aerospace Engineer and PhD student at the Indian Institute of Technology - Madras, Chennai, India. An OSS and GNU/Linux advocate, Prabhu has also contributed to VTK, the open source 3D computer graphics, image processing, and visualization system on which MayaVi is based.