I have a very nice & tricky question for you.
I need to align two meshes using a very fast algorithm. Given mesh1 and mesh2 I want to find how I need to traslate and rotate mesh1 to be in the same position of mesh2.
Firstly I did this using inertia moments of the two meshes, but the algorithm does not work if the second mesh is similar to the first one but with some missing parts. In other words, take two identical meshes and from one of them cut same parts off.
I'd like to write the code in C because I need to perform that on multiplatform machines (linux/win) and do that in a very fast way: it has to be put into a GA algorithm.
The two meshes are in STL (stereolitography) format (binary or ascii) but maybe can be useful using another kind of file format.
Do you have any idea how to perform this stuff?
question update:
first of all I want to thank you guys very much for all your suggestions. I've downloaded an install PCL on my machine and compiled the ICP (tutorial) algorithm successfully, taken from PCL web site.
But now I have some questions about that, maybe because for me is a brand new thing. what is the meaning of the 4x4 matrix output for the fitness? I should expect a rotational matrix and a traslational vector..
I hope some of you can help me.
If you need any other info please ask.
Point Cloud Library has several resources that you may find useful. As #Throwback1986 says, ICP is one excellent algorithm for aligning geometry. Pcl also features other, often faster alignment algorithms, based on identifying and matching features of interest in two pieces of geometry. The library finds a lot of use in the robotics communities, who, like you, are very performance conscious.
Pcl is written in c++. While not as portable as straight C, They offer installation instructions for windows, a few *nix flavors, and mac os. I've seen it running on ios and android as well. Check out the tutorials.
Iterative Closest Point (ICP) is one way of registering (aligning) 3D point clouds with rigid transformations. (It can also apply to meshes.)
Here is a good introduction: http://www.cs.duke.edu/courses/spring07/cps296.2/scribe_notes/lecture24.pdf
Here is a reasonable summary:
students.asl.ethz.ch/upl_pdf/314-report.pdf
Here is a matlab implementation:
http://www.mathworks.com/matlabcentral/fileexchange/12627-iterative-closest-point-method
Here are some potential optimizations:
http://www.cs.princeton.edu/~smr/papers/fasticp/
Related
I am testing some convolution algorithms i found in some sites but none of them apply the matrix filters as it should.
I am writing a very simple 24 bits bmp library on my own, but now i need a little help with the convolution, i don't need FFT or complex algorithm, running time is not important at this time.
The last code i was testing was this: http://lodev.org/cgtutor/filtering.html But i didn't work fine.
Could some one indicate me a code or algorithm in C?.
Thank you very much.
You can have a look at this algorithm - this is the closest which i can find:
Convolution to blur the image
Know that the basic convolution algorithm is more or less the same, the affect changes only by the kernel values.
There is an open source C# library which provides methods to perform image convolution of simple filters. It would be an easy port to C.
The actual methods to perform convolution can be found here. The BitmapContext class is used to just wrap a pointer to bitmap. I believe in C# this is treated as int*, so this code is operating on 4 bytes at a time.
I created Image Convolution library for simple cases - https://github.com/RoyiAvital/Projects/tree/master/ImageConvolution.
It is pretty fast (OpenMP + SIMD).
Though I'm not an advanced programmer of something, just tried doing it to do first steps in utilizing SIMD.
Still, from what can be seen in VS 2015, the CPU utilization is pretty good.
If you have ideas to make it even faster, I will be happy.
Feel free to use it in any manner you'd like.
I am developing an algorithm for an audio application for mobile platforms. It appears to me that currently the float point calculation support on many mobile processors is not ubiquitous and developing in fixed point would be a safer bet.
I have written FFT routines in float point form for some time now to a degree of success, however writing one in fixed point turned out to be rather difficult. Namely, I would be happy to improve the precision, as well as to find a way to handle potential overflows. The problem is, unlike float point FFTs, descriptions of fixed point FFT algorithms are hard to come by on the Internet.
Has anyone had some experience developing such algorithms?
Your first choice should probably be to use a native-optimized FFT. There are processing requirement for fixed point FFTs that are difficult to express efficiently in portable C (or any language probably): saturation arithmetic is probably the biggest obstacle. Assembly libraries will tend to take advantage of processor-specific instructions for these .
If you still want a portable ANSI C fixed point FFT, I only know of one choice: kissfft. (Disclaimer : I wrote it)
I have read great things about http://anthonix.com/ffts/index.html - this works well on mobile platforms - The site contains benchmarks
I have been working on an automated tool that converts floating-point C code to fixed-point, with a variety of options for tradeoffs between accuracy and execution time. I have had good results with a number of algorithms, including a 2D 8x8 discrete cosine transform. My target platform is typically an ARM Cortex-M processor but similar results should be achievable on other platforms. Would you be interested in letting me take a crack at your FFT?
I'm planning on doing a small project involving ECG signals. I am currently getting ECG signals via a COM port and recording these in a txt file using C programming.
My next step is to be able to plot all those data points in real-time. Can this be done using C programming? If not, I do not mind collecting a sample that is 2 minutes long and then plotting those data points.
After that, I want to be able to take the FFT of the time-domain data and be able to plot the frequency plot.
My end goal is to design a GUI using C, that shows a person the real-time EEG waveform as well as the frequency plot.
I did make another post and was advised to try:
RRDTool (http://oss.oetiker.ch/rrdtool/) : However, this doesn't seem to be a straightforward implementation for C.
OpenGL Utility Toolkit (http://www.opengl.org/resources/libraries/glut/) : This seems to be really powerful for generating 3D plots. However, I couldn't find helpful guides simplifying 2D plot implementations
KST : http://kst-plot.kde.org/ , This was the most interesting software. I've played around with it a bit and like it's simplicity. It also allows me to get FFT data. However, I'm not sure how to connect it with my end goal of having the GUI since it is a seperate program.
If someone could recommend C based implementation and some tutorials/sample code to go along with it that would be great. Additionally, advice on other alternatives to reach my end-goal would also be much appreciated !
I can suggest using SDL. It's more 2d based and easier to learn than OpenGL, written in C and quite powerful.
If you want you can first try out SDL in Python using pygame.
Qt http://qt.nokia.com/products/ has a plot widget that you could use ... and has language bindings for many languages
You might want to look at PLplot. Works with many languages, including C, on all the common desktop operating systems (Mac, Windows, Linux, Unix). There are quite a few examples, and most (if not all) examples are available in a number of different languages.
It is summer, and so I have decided to take it upon myself to write a data-compression program, preferably in C code. I have a decent beginners understanding of how compression works. I just have a few questions:
1) Would c be a suitable programming language to accomplish this task?
2) Should I be working in byte's with the input file? Or at a binary level somehow?
If someone could just give me a nudge in the correct direction, I'd really appreciate it. I would like to code this myself however, and not use a pre-existing compression library or anything like that.
You could start by looking at Huffman Encoding. A lot of computer science classes implement that as a project so it should be manageable. C would be appropriate for Huffman encoding, but it might be easier to do it first in a higher-level language so that you understand the concepts.There are slides, hints, and an example project available in Java for a masters-level project at the University of Pennsylvania (search for "huff" on that page).
To answer your questions:
C is suitable.
It depends on the algorithm, or the way you are thinking about `compression'.
My opinion will be, first decide whether you want to do a lossless compression or a lossy compression, then pick an algorithm to implement. Here are a few pointers:
For the lossless one, some are very intuitive, such as the run-length encoding,
e.g., if there is 11 as and 5 bs, you just encode them as 11a5b.
Some algorithms use a dictionary, please refer to LZW encoding.
Finally, I do recommend Huffman encoding since it is very straight-forward, simple and helpful to gain experience in learning algorithm (for your educational purpose).
For lossy ones, Discrete Fourier Transform (DFT), or wavelet, is used in JPEG compression. This is useful to understand multimedia compression.
Wikipedia page is a good starting point.
Yes, C is well suited for this kind of work.
Whether you work with bytes or bits will depend on the algorithm that you decide to implement. For example, Huffman coding is inherently bit-oriented whereas many other compression algorithms are not.
C is a great choice for writing a compression program. You can use plenty of other languages too, though.
Your computer probably can't directly address units of memory smaller than a byte (pretty much by definition), so working with bytes is probably a good choice. Some of how you work with the data will be affected by the compression algorithm you choose.
Good luck!
1) Would c be a suitable programming language to accomplish this task?
Yes.
2) Should I be working in byte's with the input file? Or at a binary level somehow?
They're the same, so the question makes no sense.
not use a pre-existing compression library
Can you use a pre-existing compression algorithm? There are dozens and "compression algorithm" -- when used with Google -- will reveal a great deal of helpful information.
Where Can I find algorithm details for holistic word recognition? I need to build a simple OCR system in hardware (FPGAs actually), and the scientific journals seems so abstract?
Are there any open source (open core) codes for holistic word recognition?
Thanks
For an algorithm that is quite suitable for FPGA implementation (embarrassingly parallel) you might look at:
http://en.wikipedia.org/wiki/Cross-correlation
It is fast, and easily implemented.
The only thing is: it recognizes a shape (in your case some text) DEPENDENT of the rotation and size / stretch / skew etc. But if that isn't a problem, it can be very fast and is quite robust. You should only watch out for interpretation problems with characters that are similar (like o and c).
I used it to find default texts on scanned forms to obtain bearings where Region of Interests are and searching in those images (6M pixels) only took around 15 ms with our implementation on a Core2 CPU in a single thread.