On 2007-09-17 20:24-0400 Charles Parker wrote: > Hello plplot community :^)
Welcome to the list. > > I have two questions w/ regards to the functionality of the plplot C++ > bindings. > > First, is it possible to plot single pixels in scatter plot (plpoin)? I've > tried using a lot of the different symbols and changing the size of those > symbols (with plssym), but I can't seem to find a combination that will just > turn on a single pixel for each data point I plot. I have discovered recently that some devices (e.g., the pscairo device that is part of the new cairo device driver family) honor font hinting. One characteristic of font hinting is it aligns characters with the pixel grid. I don't know what happens for small characters, but I assume you would get an equal hit on 4 pixels or a hit on one pixel. Anyhow, try pscairo (from latest svn) and see whether it helps. When viewing the results you will have to turn off antialiasing in your PostScript viewer to see exactly which pixels have been painted. For devices that don't honor font hinting, world coordinates are not going to be aligned with pixel coordinates so more than one pixel will be involved when painting a dot at arbitrary x, y. However, from the known pixel range of your device, you should be able to do your own pixel alignment by carefully choosing plvpor values and world coordinates so the latter match integer pixel values. Then it is only a matter of taking the nearest integral value for the x and y positions to get consistent alignment on pixels. Under those circumstances, your tiny characters should always at least look the same, and may even correspond to painting a single pixel for the no antialiasing case. > > Second, I'm going to be plotting about 5000 data points or so, the problem > is that the way my data are structured, the points I need to plot are not > stored sequentially in memory. I have data with about 15 parameters per > point, and I only want to plot points (the x and y are two of the > parameters) that satisfy some filtering criteria. Am I better off simply > taking the memory and performance hit to create an additional data structure > in which these data are sequential? Or can I simply call plpoin to plot each > individual point? In the latter case I would loop through the data only once > and plot points as I found them, whereas in the former there is the extra > overhead of creating the data structure and copying the data before I can > plot it. I think the speed for unordered access will depend on the size of your cache and the degree of non-locality of reference. Taking data out of order may actually make little difference at all. Regardless of that, I always try as a general rule to use the simplest programming to prototype what I want and optimize further (with the associated increased danger of introducing bugs) only if really necessary. Anyhow, that is what I suggest in the present case. Alan __________________________ Alan W. Irwin Astronomical research affiliation with Department of Physics and Astronomy, University of Victoria (astrowww.phys.uvic.ca). Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); PLplot scientific plotting software package (plplot.org); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________ ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Plplot-general mailing list Plplot-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-general
