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Re: Drawing Graphs

by PhiRatE (Monk)
on Sep 12, 2002 at 23:07 UTC ( #197385=note: print w/replies, xml ) Need Help??

in reply to Drawing Graphs

There are a few cavets to GD::Graph. The most obvious is the lack of antialiasing, this makes for acceptable web graphics, but not brilliant. For example:

Displays a couple of charts from a custom graphics engine (the basis is actually imlib2), with antialiased lines and a nice semi-transparent underlay.

Displays a pretty extreme example, this one generated from perl through povray, I had standard, bar and stacked versions of that engine. Disadvantage is its pretty unreadable for real stats, but it looks nice :)

So basically you have a number of questions to answer:

1. Who is the target audience? are they going to require particularly impressive graphics?

2. Are the graphics for general trend information or precise analysis?

3. Are the graphics going to be require in realtime? near realtime? any old time?

4. Do you have a lot of time to muck about with it?

5. Is there going to be a lot of different composits on any given chart (ie, bars and a min/max/median line etc)?

Have a think about those, they should point you in the relevant direction in terms of work required. GD is by far the easiest, but you pay for that in terms of simple graphics. Moving to ImLib2 or OpenGL as your rendering basis makes for harder code but a nicer end result (and often faster). Going to povray/rib is really not recommended (from experience :) :)

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Re: Re: Drawing Graphs
by oakbox (Chaplain) on Sep 15, 2002 at 11:03 UTC
    I, also, went with the POV-Ray route. I ended up spending a LOT of hours getting the information into a format that was pretty, but still easily readable. This wasn't just a case of reinventing the wheel, this was inventing mining, smelting, and wood working. The fact that POV-Ray takes its instructions from a text source file made it pretty easy to integrate into my final script, but the development time was prohibitive.
    Just my 2 cents.

    Update Posted an example of my code here: POV-Ray graphing example


      PhiRatE or oakbox, is the Perl code you used to generate the POV-Ray scene file for the graphs available somewhere? Being an old POV-Ray fan I'd like to see how you generated the scene file, specifically the camera def...

      (Edit: clarification of request)--Sorry, Beatnik.
      My original, poorly worded question, wonderfully answered by Beatnik was:

      Is the POV-Ray code available somewhere?
      May the Source be with you.

      You said you wanted to be around when I made a mistake; well, this could be it, sweetheart.

        Okay, this needs some explanation. This script was created to look into a directory storing files. Each of these Storable files has a hash reference for the results of tests. (This was part of the psychological profiling system I am working on for Each of these graphs takes between 5 and 30 seconds to render, so I was running this in the background as a cron job, pre-rendering the graphs so that when they are needed, they are already on the system and ready for download via the web.

        How it works:
        Pull up my values to graph (all results are between 1 and 9).
        Send those values to the Builder.
        The Builder tries to adjust the width of the bars to make them fit into the final image and then creates a POV source file.
        After the source file is built, return to the main program and run a system call to create the png output file.

        This was just a proof of concept. In the end, my customers weren't too happy with the look. It is very difficult (as mentioned earlier) to represent this kind of information in a clean way in 3D. Hopefully, you can use this code for some ideas and as a jumping-off point for your own code.

        Note! I made a few changes to this code before posting it here and I haven't tested my changes. I can't guarantee the prettiness either :)

        I put an example of the output (before fiddling with the source) here:

        #!/usr/bin/perl use strict; no strict 'refs'; use Storable qw(retrieve nstore); my $dir = "/source/of/data/files/storable"; my $outputdir = "/dir/for/images/povtrace"; chdir $dir || (warn "Cannot chdir $dir: $!" and return); opendir(DIR, $dir) || (warn "Cannot open $dir: $!" and return); my @contents = readdir DIR; closedir(DIR); foreach my $f (@contents) { if($f !~ /candidateinfo/){ # not looking at candidates! my $file = $dir."/".$f; # the file # get test ID my ($can,$tg) = split(/-/,$f); if($can < 200){next;} # only recent candidates my ($tid,undef) = split(/\./,$tg); if($tid eq ""){next;} # filter kooky files my $Test = eval{retrieve($file)}; # read the storable my $scorecant; my @xdata; my @ydata; foreach my $tcode (sort keys %{$Test->{norms}}){ push(@xdata,$Test->{norms}->{$tcode}); push(@ydata,$Test->{expert_names}->{$tcode}); $scorecant .= "$Test->{norms}->{$tcode}"; } my $ccc = @ydata; if($ccc <1){next;} $ccc = @xdata; if($ccc <1){next;} my $outfile = "$outputdir/$tid-$scorecant.png"; if(-e($outfile)){ next; } # I've already graphed this result set # build the POV-Ray source file &Builder(\@xdata,\@ydata,"$tid-$scorecant.pov"); # Render that source file, the settings below are # a balance between speed and pretty my $povcall = qq( povray +L/home/oakbox/tmp/povray-3.5/include +A ++I$tid-$scorecant.pov +O$outfile +V +W400 +H300 +FN6); my $whang = system("$povcall 1>povray.stdout 2>povray.stderr"); } } exit; sub Builder { my ($xdata,$ydata,$renderfilename) = @_; my @xdata; my @ydata; my $number_vert_lines = 9; # this is a kludge, but I'm in a hurry foreach ( @{$xdata} ){ push(@xdata,$_);} foreach ( @{$ydata} ){ push(@ydata,$_);} # make sure that I have an x for every y my $county = @ydata; my $countx = @xdata; if($countx ne $county){ die "Your x and y counts don't add up!"; } # find height scaling factor my $maxyval = 9 ; my $heightscale = 4 / $maxyval; my $ylabels; foreach my $level (0...$number_vert_lines){ my $label = ($level/$number_vert_lines) * $maxyval; $label = sprintf("%.1f", $label); my $lineup = ($level/$number_vert_lines) * 4; $ylabels .= qq( text { ttf "Arial.ttf" "$label" .1, 0 pigment { Black } scale .15 translate <-.7,$lineup,0> rotate <0,350,0> } object { Divide_Line translate <-.5,$lineup,0>} ); } # calculate dividers and bar width my $widthval = 6 / $county; if($widthval > 2){$widthval=2;} my $yspace = $widthval * .8; # make bar declarations one for each y value my @colorseq = ("Blue","Green","Red","Blue","Green","Red","Blue","Gree +n","Red","Blue","Green","Red","Blue","Green","Red","Blue","Green","Re +d","Blue","Green","Red","Blue","Green","Red","Blue","Green","Red","Bl +ue","Green","Red","Blue","Green","Red","Blue","Green","Red","Blue","G +reen","Red","Blue","Green","Red","Blue","Green","Red","Blue","Green", +"Red","Blue","Green","Red","Blue","Green","Red","Blue","Green","Red", +"Blue","Green","Red","Blue","Green","Red"); my $bar_descriptors; my $tscale_factor = ".01"; my $scale_factor = .20; my $theight = -.15; foreach my $placeh (0...$#ydata){ my $barheight = $xdata[$placeh] * $heightscale; $barheight = sprintf("%.2f", $barheight); my $yplace = $placeh * $widthval; $yplace = sprintf("%.2f", $yplace); my $interior_lights; foreach my $lights (0){ # only one light now, but easy to add! if($lights < $barheight){ my $bong = $lights + .1; $interior_lights.=qq( light_source { <.1,$bong,.2> color White } ); }} my $tplace = $yplace + ($yspace/2); $bar_descriptors.=qq( #declare Bar_$placeh = merge { cylinder { <0,$barheight,0>, <0,0,0>, .2 finish { Dull } pigment { $colorseq[$placeh] filter .5} interior{ ior 1.5 fade_distance 5 fade_power .5 caustics 1 } } $interior_lights bounded_by { box {<0,0,0>, <$yspace,$barheight,1>} } } object { Bar_$placeh translate <$yplace,0,0> } text { ttf "Arial.ttf" "$ydata[$placeh]" .15, 0 pigment { $colorseq[$placeh] } scale $scale_factor translate <.15,$theight,0> rotate <0,20,350> translate <$tplace,0,0> } ); # $scale_factor = $scale_factor + $tscale_factor; # $theight = $theight + $tscale_factor; } my $final_output = qq( #include "" #include "" camera { location <.7,2.5,-6.5> look_at <2.4,1.9,0> } background { White } global_settings { max_trace_level 30 } light_source { <0, 50, -50> color White shadowless } #declare Divide_Line = box { <0,0,-.1>, <7,-.015,-.12> pigment { Gray05 } } $ylabels $bar_descriptors ); open (WRT,">$renderfilename"); print WRT $final_output; close(WRT); } exit;


        The Pov-Ray Download section has a few links.

        ...Perl is like sex: if you're doing it wrong, there's no fun to it.

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