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I think here, "practicality" means "has a library for controlling robots". Also a good numeric library, a good matlab-like graphing library, good 3D graphics, g

• palish 18y ago
  Just curious, which library are you referring to when you say "good 3D graphics"? I'm writing a graphics engine using PyOpenGL, but that's just a minimalist wrapper over the standard OpenGL API that's available for dozens of languages.
  • tlb 18y ago
    Yes, I use PyOpenGL in GTK (with GTKGLExt). People have said good things about Gazebo, but I haven't used it. Most of the 3D stuff is performance-critical, so I typically prototype in Python and then convert to C++, which for graphics code isn't too painful. The Boost.Python interface makes it pretty easy. Also, the Cairo graphics interface is wonderful for drawing charts, animated robot stick figures, and many other visualizations. It has a full Postscript rendering model with alpha blending. It looks like PLT Scheme has an OpenGL binding too, though I haven't seen it used. It looks very low-level, for instance it has separate methods named: gl.Vertex3d gl.Vertex3dv gl.Vertex3f gl.Vertex3fv gl.Vertex3i gl.Vertex3iv gl.Vertex3s gl.Vertex3sv
    • palish 18y ago
      Nice. Yeah, the GL graphics code is pretty easy to convert to C++ when performance matters. It's wonderful to quickly prototype graphics code in Python with full error checking. Also, if you haven't used it yet, check out Py++. It takes a lot of the pain out of hand-authoring a Boost.Python code file. I'm using Py++ to automatically generate Boost.Python bindings for the C++ library FCollada. (FCollada is a library for accessing 3D modeling data exported into the .dae COLLADA format.) Thanks for the tip about Cairo. Also, glVertex3d, 3dv, 3f, etc are part of the standard GL API. The 'd' suffix indicates 'double', 'f' indicates 'float', 'i' indicates 'int', 's' indicates 'short', and the 'v' suffix indicates that the function accepts a pointer rather than 3 separate components passed by value. Of course, the glVertex* API has been deprecated because VBOs are far more efficient. Just curious again, why do you use OpenGL for Anybots? Do you create simulations before building new robot prototypes?
      • tlb 18y ago
        My point was there's no single 'gl.Vertex3' call that takes native Lisp numbers. Thinking about double/float/int/short should be abstracted out below the Lisp level. We use OpenGL to show real-time renderings of the robot, derived from the gyros and joint angle sensors. We have an analysis tool that shows, either in real time or post-run analysis, renderings synchronized with high-speed video of the robot and scrolling strip charts of every important variable over time. I always see much more looking at slow-motion videos & renderings afterwards than looking at the real robot. OpenGL rendering also turned out to be useful for extracting data from CAD models. Our CAD software (SolidWorks) can export STL files (a list of polygons) and we need to extract center of mass and moment of inertia and such. Doing that without visualizing it is a nightmare. We have done dynamics simulations (using ODE), but they haven't had much predictive value.
        • palish 18y ago
          Ah. Very cool. Are you computing center of mass / moment of inertia yourself, or using a 3rd party library to do it? PhysX is free, and I believe it can do those calculations for you fairly automatically. (In PhysX, a 'scene' is composed of 'actors', and each actor is described by a set of shape descriptors. A shape descriptor can represent a box, a sphere, a capsule, a convex hull, etc. So a laptop actor could crudely be approximated with two box shape descriptors (one for the screen, one for the body) connected by a joint. Given those shape descriptors, the library calculates the actor's center of mass / moment of inertia / etc. If your CAD software simply exports a list of polygons, you'll need to decompose those into a set of convex hulls using convex hull decomposition techniques: http://codesuppository.blogspot.com/2006/04/approximate-convex-decomposition.html http://codesuppository.blogspot.com/2006/04/approximate-conv... ) You also might have better luck running dynamics simulations with PhysX than with ODE. It comes with a large number of code examples to get you started: http://developer.nvidia.com/object/physx_downloads.html http://developer.nvidia.com/object/physx_downloads.html
          • tlb 18y ago
            I use a very simple and exact O(N) algorithm to calculate mass properties of polyhedrons without computing convex hulls or anything: http://www.cs.berkeley.edu/~jfc/mirtich/massProps.html http://www.cs.berkeley.edu/~jfc/mirtich/massProps.html Maybe 80 LOC. I'm not sure why anything more complex is needed. PhysX does seem promising.
    • anthonyb 18y ago
      For Python, there are also a number of game libraries around which you might be able to repurpose. Pyglet, Pygame and PyOgre are three which spring to mind. Depending on exactly what you're trying to do, of course...
      • drawkbox 18y ago
        Panda3D, developed by Disney and given to CMU for research. One real MMO built off of it, Pirates of the Caribbean.
        • stcredzero 18y ago
          Panda3D is quite good. It has many basic building blocks for 3D games. When I used it, docs were ok but a bit sparse in places, but you could deduce much from what was auto-generated.
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• silentbicycle 18y ago
  Rather than complaining about how everyone else is a bonehead for not using Lisp, write some libraries to make it useful for more things in the real world. Thank you. Cannot stress this enough. (Making said libraries portable helps, too!)
  • deleted 18y ago
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• mattjones 18y ago
  Libraries aren't the issue. I use Chicken Scheme for a few things, which has plenty of libraries and a fantastic package system called eggs. Sure, other languages like Perl and Python have more libraries now, but that's not what made them popular. What made them popular was the design of the core languages. I started using Ruby because it was faster to type and easier to remember how to do things than Perl, not because it had more libraries, which it didn't. The problem with Scheme is that the core language isn't terse enough, and so it gives the impression that it will be hard to do things. And that's correct. Scheme requires much more typing and is harder to remember than Ruby. Consider: Ruby: h = {} h[:foo] = "hi" h[:foo] #=> "hi" h[:bar] #=> nil Scheme (Chicken): (define h (make-hash-table)) (hash-table-set! h 'foo "hi") (hash-table-ref h 'foo) ;; "hi" (hash-table-ref/default h 'bar #f) ;; #f That, in a nutshell, is why people don't use Scheme. The people who made Perl etc. popular hate typing, and the core language of Scheme forces you to type a ton. There are other problems like really slow string functions, things that should be core being in SRFIs, libraries being called "SRFI 18" rather than normal things like "threads" so that it's extra hard to tell where a function is coming from, where its documentation is, or what you have to import to get it. Lack of libraries (if indeed that's a problem for you) is downstream of the core problem, which is that Scheme has a lot of clumsy design features that discourage would-be library writers from using the language a lot. This isn't a Lisp problem, it's a Scheme one. A Lisp with a better core and enough users would get lots of libraries eventually, just like any language. I think Scheme is good for teaching though, and would rather learn it in a course than Python.
  • smallpaul 18y ago
    > Libraries aren't the issue You say libraries aren't the issue, but the discussion is about a blog pst that said: "And why Python, then? Well, said Sussman, it probably just had a library already implemented for the robotics interface, that was all." I'm sure your experience is grounded in a general reality. But the post you disagreed with was about a specific case: i.e. the one described in the blog post.
    • mattjones 18y ago
      From the point of view of a person at an instant in time, libraries are a concern. But when we're talking about Scheme being displaced by Python at MIT, where Scheme was developed 30 years ago, we really ought to ask what's been happening to Scheme during that 30 years. The problem, at MIT and elsewhere, is that hackers don't like hacking Scheme enough. Python has more libraries than Scheme now, but that's not the main thing that made more people use it. People use it because they prefer the language. This is something that Sussman and others at MIT should be trying to understand, but it doesn't strike me that they are trying to understand it. They're just saying "Python has a better robotics library -- oh well!" as if this were something completely random that they have no control over. That doesn't seem like the sort of attitude that produced Scheme in the first place. My point of contention with the comment I replied to is the idea that fixing the problem is a question of writing more libraries for Scheme. Writing or interfacing to libraries for numerics, 3D graphics, etc. is a trivial task compared to making a language hackers love. Now, maybe hackers' distaste for Scheme is Scheme's fault, or maybe it's hackers'; but in any case, the issue is with the core language, not the libraries. And based on my personal experience with Scheme I would say that enough of the fault lies on Scheme's side that it's worth fixing.