Re: [GD-DEVEL] Re: plotting data c++

On Friday 01 February 2008 06:11, Bill Frost wrote:
> Hi guys,
> 
> This has always sounded to me like an ideal gdLib application.
> 
> I had a bit of spare time today and I was intrigued by the problem. I dug
> out some existing C++ code and modified it a bit and it now plots Patolfo's
> data points as a square wave in JPEG format. If I keep the number of samples
> at 256 but vary the number of terms from a high, such as 128, a square wave
> is generated. If the number of terms is then set low, such as 8, a
> sinusoidal-square wave is generated. Looks nice as a curved plot!


By the way..
I should have mentioned this earlier, but there is a nice applet at

   http://www.jhu.edu/~signals/fourier2/

that does this job.  I use it in teaching Fourier series.
A more sophisticated 2D Fourier applet is also available as part
of Kevin Cowtan's tutorial on Fourier analysis in crystallography

   http://www.ysbl.york.ac.uk/~cowtan/sfapplet/sfintro.html


Neither of these has anything in particular to do with libgd, of course,
but if your primary interest was the application itself maybe these
are of use.

	Ethan







 
> Selecting 256 samples with 128 terms runs in 0.093 seconds on a Centrino, as
> gdLib / C++ is very fast.
> 
> Note that it is a utility, not a GUI application. It runs Padolfo's test
> data application and opens the file using the operating system's default
> JPEG handler (typically Windows Picture and Fax Viewer).
> 
> It:
> 
> * runs the sample algorithm,
> * saves the sample data to a file and closes it (normally user-supplied)
> * re opens the file
> * extracts all data into a class, finding max and min values
> * sets up a device context in gdLib, with some scaling
> * creates the JPEG and thumbnail
> * iterates the class and plots each x, y to a pixel
> * scales and labels the axis
> 
> 
> I've just fixed a rather embarrassing buffer overrun and I need to do a
> little code clean up and make the JPEG slightly more aesthetic. Then I'll
> post the source as a royalty free utility (seeing Padolfo wrote the main
> algorithm!) as an example of using gdLib. Comments welcome once I have done
> this as I am by no means an expert on gdLib and I still don't really know
> what FFT is all about.
> 
> Cheers,
> 
> Bill
> 
> -----Original Message-----
> From: Patolfo [mailto:[email protected]] 
> Sent: Thursday, 31 January 2008 10:15 AM
> To: Bill Frost; [email protected]
> Subject: [GD-DEVEL] Re: plotting data c++
> 
> ok guys here is the problem again, i am plotting x,y data, floats to be 
> precise, must be in C, C++, the hardway, no perl or python just know how 
> to us perl a little, the idea is to have the application data to do the 
> approximation of a square wave by means of fourier series, the job is 
> done, now the problem is the gui, well i tried tk with perl and 
> everything went smootly, till the part of converting perl to C, and 
> including the interpreter and all that stuff, truly i did not get it 
> right so it freezes and is buggy, so well back in track i found my self 
> on the same road, just C, the gui I plan to do them with windowsapi they 
> are the lesser problem, mingw, but the plotting data per se is the
> biggest problem, i tried reading the wiki for libgd, and let me tell you 
> it is not for noobs, or at least not for the dumbest as me.
> 
> The algorithm says more or less:
> number or harmonics, number of data points, using gui, some routines, 
> and then we have and arbitrary number of data with a max value of 1 and 
> the minimum of 0, arranged in pairs of x,y,
> 
> i have the suspicion it is straightforward, but i seem to fail, i am 
> still googling, found koolplot, which i think uses libgd, did not work 
> for my mingw, so, any directions where to look...
> 
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-- 
Ethan A Merritt